Network Working Group                                   J. Loughney, Ed.
Request for Comments: 3868                                         Nokia
Category: Standards Track                                  G. Sidebottom
                                                  Signatus Technologies
                                                               L. Coene
                                                             G. Verwimp
                                                           Siemens n.v.
                                                              J. Keller
                                                                Tekelec
                                                            B. Bidulock
                                                    OpenSS7 Corporation
                                                           October 2004


   Signalling Connection Control Part User Adaptation Layer (SUA)

Status of this Memo

  This document specifies an Internet standards track protocol for the
  Internet community, and requests discussion and suggestions for
  improvements.  Please refer to the current edition of the "Internet
  Official Protocol Standards" (STD 1) for the standardization state
  and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

  Copyright (C) The Internet Society (2004).

Abstract

  This document defines a protocol for the transport of any Signalling
  Connection Control Part-User signalling over IP using the Stream
  Control Transmission Protocol.  The protocol is designed to be
  modular and symmetric, to allow it to work in diverse architectures,
  such as a Signalling Gateway to IP Signalling Endpoint architecture
  as well as a peer-to-peer IP Signalling Endpoint architecture.















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RFC 3868                          SUA                       October 2004


Table of Contents

  1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
      1.1.  Scope. . . . . . . . . . . . . . . . . . . . . . . . . .  3
      1.2.  Abbreviations and Terminology. . . . . . . . . . . . . .  4
      1.3.  Signalling Transport Architecture. . . . . . . . . . . .  6
      1.4.  Services Provided by the SUA Layer . . . . . . . . . . .  9
      1.5.  Internal Functions Provided in the SUA Layer . . . . . . 11
      1.6.  Definition of SUA Boundaries . . . . . . . . . . . . . . 14
  2.  Conventions. . . . . . . . . . . . . . . . . . . . . . . . . . 19
  3.  Protocol Elements. . . . . . . . . . . . . . . . . . . . . . . 19
      3.1.  Common Message Header. . . . . . . . . . . . . . . . . . 20
      3.2.  SUA Connectionless Messages. . . . . . . . . . . . . . . 24
      3.3.  Connection Oriented Messages . . . . . . . . . . . . . . 27
      3.4.  Signalling Network Management (SNM) Messages . . . . . . 42
      3.5.  Application Server Process State Maintenance Messages. . 49
      3.6.  ASP Traffic Maintenance Messages . . . . . . . . . . . . 53
      3.7.  SUA Management Messages. . . . . . . . . . . . . . . . . 56
      3.8.  Routing Key Management (RKM) Messages. . . . . . . . . . 58
      3.9.  Common Parameters. . . . . . . . . . . . . . . . . . . . 61
      3.10. SUA-Specific parameters. . . . . . . . . . . . . . . . . 74
  4.  Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 92
      4.1.  Procedures to Support the SUA-User Layer . . . . . . . . 92
      4.2.  Receipt of Primitives from the Layer Management. . . . . 93
      4.3.  AS and ASP State Maintenance . . . . . . . . . . . . . . 95
      4.4.  Routing Key Management Procedures. . . . . . . . . . . .109
      4.5.  Availability and/or Congestion Status of SS7
            Destination Support101 . . . . . . . . . . . . . . . . .112
      4.6.  MTP3 Restart . . . . . . . . . . . . . . . . . . . . . .115
      4.7.  SCCP - SUA Interworking at the SG. . . . . . . . . . . .115
  5.  Examples of SUA Procedures . . . . . . . . . . . . . . . . . .117
      5.1.  SG Architecture. . . . . . . . . . . . . . . . . . . . .117
      5.2   IPSP Examples. . . . . . . . . . . . . . . . . . . . . .119
  6.  Security Considerations. . . . . . . . . . . . . . . . . . . .121
  7.  IANA Considerations. . . . . . . . . . . . . . . . . . . . . .121
      7.1.  SCTP Payload Protocol ID . . . . . . . . . . . . . . . .121
      7.2.  Port Number. . . . . . . . . . . . . . . . . . . . . . .121
      7.3.  Protocol Extensions. . . . . . . . . . . . . . . . . . .121
  8.  Timer Values . . . . . . . . . . . . . . . . . . . . . . . . .123
  9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .123
  10. References . . . . . . . . . . . . . . . . . . . . . . . . . .123
      10.1. Normative References . . . . . . . . . . . . . . . . . .123
      10.2. Informative References . . . . . . . . . . . . . . . . .124








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  Appendix A.  Signalling Network Architecture . . . . . . . . . . .125
      A.1.  Generalized Peer-to-Peer Network Architecture. . . . . .125
      A.2.  Signalling Gateway Network Architecture. . . . . . . . .126
      A.3.  Signalling Gateway Message Distribution
            Recommendations. . . . . . . . . . . . . . . . . . . . .128
  Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .129
  Full Copyright Statement . . . . . . . . . . . . . . . . . . . . .131

1.  Introduction

  There is ongoing integration of switched circuit networks and IP
  networks.  Network service providers are designing IP-based
  signalling architectures that need support for SS7 and SS7-like
  signalling protocols.  IP provides an effective way to transport user
  data and for operators to expand their networks and build new
  services.  In these networks, there is need for interworking between
  the SS7 and IP domains [2719].

  This document defines a protocol for the transport SS7 SCCP-User
  protocols [ANSI SCCP] [ITU SCCP], such as TCAP and RANAP, over IP
  using the Stream Control Transmission Protocol (SCTP) [2960].

1.1.  Scope

  This document details the delivery of SCCP-user messages (MAP & CAP
  over TCAP [ANSI TCAP] [ITU TCAP], RANAP [RANAP], etc.) messages over
  IP between two signalling endpoints.  Consideration is given for the
  transport from a signalling gateway to an IP signalling node (such as
  an IP-resident Database) as described in the Framework Architecture
  for Signalling Transport [2719].  This protocol can also support
  transport of SCCP-user messages between two endpoints wholly
  contained within an IP network.

  The delivery mechanism addresses the following criteria:

  *  Support for transfer of SCCP-User Part messages
  *  Support for SCCP connectionless service.
  *  Support for SCCP connection oriented service.
  *  Support for the operation of SCCP-User protocol peers.
  *  Support for the management of SCTP transport associations between
     signalling gateways and IP-based signalling nodes.
  *  Support for distributed IP-based signalling nodes.
  *  Support for the asynchronous reporting of status changes to
     management functions.







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1.2.  Abbreviations and Terminology

1.2.1.  Abbreviations

  CAP - CAMEL Application Protocol.

  GTT - Global Title Translation.

  MAP - Mobile Application Protocol.

  PC - Signalling System no. 7 Point Code.

  RANAP - Radio Access Network Application Protocol.

  SCTP - Stream Control Transmission Protocol.

  SS7 - Signalling System no. 7.

  TCAP - Transaction Capabilities Application Protocol.

1.2.2.  Terminology

  Signalling Gateway (SG) - Network element that terminates switched
  circuit networks and transports SCCP-User signalling over IP to an IP
  signalling endpoint.  A Signalling Gateway could be modeled as one or
  more Signalling Gateway Processes, which are located at the border of
  the SS7 and IP networks.  Where an SG contains more than one SGP, the
  SG is a logical entity and the contained SGPs are assumed to be
  coordinated into a single management view to the SS7 network and to
  the supported Application Servers.

  Application Server (AS) - A logical entity serving a specific Routing
  Key.  An example of an Application Server is a virtual IP database
  element handling all requests for an SCCP-user.  The AS contains a
  set of one or more unique Application Server Processes, of which one
  or more is normally actively processing traffic.

  Application Server Process (ASP) - An Application Server Process
  serves as an active or backup process of an Application Server (e.g.,
  part of a distributed signalling node or database element). Examples
  of ASPs are MGCs, IP SCPs, or IP-based HLRs.  An ASP contains an SCTP
  endpoint and may be configured to process traffic within more than
  one Application Server.

  IP Server Process (IPSP) - A process instance of an IP-based
  application.  An IPSP is essentially the same as an ASP, except that
  it uses SUA in a peer-to-peer fashion.  Conceptually, an IPSP does
  not use the services of a Signalling Gateway.



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RFC 3868                          SUA                       October 2004


  Signalling Gateway Process (SGP) - A process instance of a Signalling
  Gateway.  It serves as an active, load-sharing or broadcast process
  of a Signalling Gateway.

  Signalling Process - A process instance that uses SUA to communicate
  with other signalling process.  An ASP, a SGP and an IPSP are all
  signalling processes.

  Association - An association refers to an SCTP association.  The
  association provides the transport for the delivery of SCCP-User
  protocol data units and SUA layer peer messages.

  Routing Key - The Routing Key describes a set of SS7 parameters
  and/or parameter ranges that uniquely defines the range of signalling
  traffic configured to be handled by a particular Application Server.
  An example would be where a Routing Key consists of a particular SS7
  SCCP SSN plus an identifier to uniquely mark the network that the SSN
  belongs to, for which all traffic would be directed to a particular
  Application Server.  Routing Keys are mutually exclusive in the sense
  that a received SS7 signalling message cannot be directed to more
  than one Routing Key.  Routing Keys can be provisioned, for example,
  by a MIB or registered using SUA's dynamic registration procedures.
  Routing keys MUST NOT span multiple network appearances.

  Routing Context - An Application Server Process may be configured to
  process traffic within more than one Application Server.  In this
  case, the Routing Context parameter is exchanged between the SGP and
  the ASP (or between two ASPs), identifying the relevant Application
  Server.  From the perspective of an SGP/ASP, the Routing Context
  uniquely identifies the range of traffic associated with a particular
  Application Server, which the ASP is configured to receive.  There is
  a 1:1 relationship between a Routing Context value and a Routing Key
  within an AS.  Therefore the Routing Context can be viewed as an
  index into an AS Table containing the AS Routing Keys.

  Address Mapping Function (AMF) - The AMF is an implementation
  dependent function that is responsible for resolving the address
  presented in the incoming SCCP/SUA message to correct SCTP
  association for the desired endpoint.  The AMF MAY use routing
  context / routing key information as selection criteria for the
  appropriate SCTP association.

  Fail-over - The capability to reroute signalling traffic as required
  to an alternate Application Server Process, or group of ASPs, within
  an Application Server in the event of failure or unavailability of a
  currently used Application Server Process. Fail-over may apply upon
  the return to service of a previously unavailable Application Server
  Process.



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  Host - The computing platform that the SGP or ASP process is running
  on.

  Layer Management - Layer Management is a nodal function that handles
  the inputs and outputs between the SUA layer and a local management
  entity.

  Network Appearance - The Network Appearance is an SUA local reference
  (typically an integer) shared by SG and AS that together with a
  Signalling Point Code uniquely identifies an SS7 node by indicating
  the specific SS7 network it belongs to.

  Network Byte Order - Most significant byte first, a.k.a. Big Endian.

  Stream - A stream refers to an SCTP stream; a unidirectional logical
  channel established from one SCTP endpoint to another associated SCTP
  endpoint, within which all user messages are delivered sequenced
  except for those submitted to the unordered delivery service.

  Transport address - an address that serves as a source or destination
  for the unreliable packet transport service used by SCTP.  In IP
  networks, a transport address is defined by the combination of an IP
  address and an SCTP port number.  Note, only one SCTP port may be
  defined for each endpoint, but each SCTP endpoint may have multiple
  IP addresses.

1.3.  Signalling Transport Architecture

  The framework architecture that has been defined for switched circuit
  networks signalling transport over IP [2719] uses multiple
  components, including an IP transport protocol, a signalling common
  transport protocol and an adaptation module to support the services
  expected by a particular switched circuit networks signalling
  protocol from its underlying protocol layer.

  In general terms, the SUA architecture can be modeled as a peer-to-
  peer architecture.  The first section considers the SS7 to IP
  interworking architectures for connectionless and connection-oriented
  transport.  For this case, it is assumed that the ASP initiates the
  establishment of the SCTP association with SG.

1.3.1.  Protocol Architecture for Connectionless Transport

  In this architecture, the SCCP and SUA layers interface in the SG.
  Interworking between the SCCP and SUA layers is needed to provide for
  the transfer of the user messages as well as the management messages.





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RFC 3868                          SUA                       October 2004


     ********   SS7   ***************   IP   ********
     * SEP  *---------*             *--------*      *
     *  or  *         *      SG     *        * ASP  *
     * STP  *         *             *        *      *
     ********         ***************        ********

     +------+                                +------+
     | SUAP |                                | SUAP |
     +------+         +------+------+        +------+
     | SCCP |         | SCCP | SUA  |        | SUA  |
     +------+         +------+------+        +------+
     | MTP3 |         | MTP3 |      |        |      |
     +------+         +------+ SCTP |        | SCTP |
     | MTP2 |         | MTP2 |      |        |      |
     +------+         +------+------+        +------+
     |  L1  |         |  L1  |  IP  |        |  IP  |
     +------+         +------+------+        +------+
         |               |         |            |
         +---------------+         +------------+

       SUAP - SCCP/SUA User Protocol (TCAP, for example)
       STP  - SS7 Signalling Transfer Point

  See Appendix A.3.1 for operation recommendations.

1.3.1.1.  SG as endpoint

  In this case, the connectionless SCCP messages are routed on point
  code (PC) and subsystem number (SSN).  The subsystem identified by
  SSN and Routing Context is regarded as local to the SG.  This means
  from SS7 point of view, the SCCP-user is located at the SG.

1.3.1.2.  Signalling Gateway as relay-point

  A Global Title translation is executed at the signalling gateway,
  before the destination of the message can be determined.  The actual
  location of the SCCP-user is irrelevant to the SS7 network.  GT
  Translation yields an "SCCP entity set", from which an Application
  Server can be derived.  Selection of the Application Server is based
  on the SCCP called party address (and possibly other SS7 parameters
  depending on the implementation).










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1.3.2.  Protocol Architecture for Connection-Oriented Transport

  In this architecture, the SCCP and SUA layers share an interface in
  the signalling gateway process to associate the two connection
  sections needed for the connection-oriented data transfer between SEP
  and ASP.  Both connection sections are setup when routing the Connect
  Request messages from the signalling end point via signalling gateway
  process to ASP and visa versa.  The routing of the Connect Request
  message is performed in the same way as described in 1.3.1.

     ********   SS7   ***************   IP   ********
     * SEP/ *---------*      SG     *--------* ASP  *
     * STP  *         *             *        *      *
     ********         ***************        ********

     +------+                                +------+
     | SUAP |                                | SUAP |
     +------+         +------+------+        +------+
     | SCCP |         | SCCP | SUA  |        | SUA  |
     +------+         +------+------+        +------+
     | MTP3 |         | MTP3 |      |        |      |
     +------|         +------+ SCTP |        | SCTP |
     | MTP2 |         | MTP2 |      |        |      |
     +------+         +------+------+        +------+
     |  L1  |         |  L1  |  IP  |        |  IP  |
     +------+         +------+------+        +------+
         |               |         |            |
         +---------------+         +------------+

       SUAP - SCCP/SUA Application Protocol (e.g., - RANAP/RNSAP)
       STP  - SS7 Signalling Transfer Point

  See Appendix A.3.2 for operation recommendations.

1.3.3.  All IP Architecture

  This architecture can be used to carry a protocol that uses the
  transport services of SCCP within an IP network.  This allows
  flexibility in developing networks, especially when interaction
  between legacy signalling is not needed.  The architecture removes
  the need for signalling gateway functionality.










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RFC 3868                          SUA                       October 2004


     ********   IP   ********
     * IPSP *--------* IPSP *
     ********        ********

     +------+        +------+
     | SUAP |        | SUAP |
     +------+        +------+
     | SUA  |        | SUA  |
     +------+        +------+
     | SCTP |        | SCTP |
     +------+        +------+
     |  IP  |        |  IP  |
     +------+        +------+
        |                |
        +----------------+

     SUAP - SCCP/SUA Application Protocol (e.g., - RANAP/RNSAP)

1.3.4.  ASP Fail-over Model and Terminology

  The SUA protocol supports ASP fail-over functions to support a high
  availability of transaction processing capability.

  An Application Server can be considered as a list of all ASPs
  configured/registered to handle SCCP-user messages within a certain
  range of routing information, known as a Routing Key.  One or more
  ASPs in the list may normally be active to handle traffic, while
  others may be inactive but available in the event of failure or
  unavailability of the active ASP(s).

  For operation recommendations, see Appendix A.

1.4.  Services Provided by the SUA Layer

1.4.1.  Support for the transport of SCCP-User Messages

  The SUA supports the transfer of SCCP-user messages.  The SUA layer
  at the signalling gateway and at the ASP support the seamless
  transport of user messages between the signalling gateway and the
  ASP.

1.4.2.  SCCP Protocol Class Support

  Depending upon the SCCP-users supported, the SUA supports the 4
  possible SCCP protocol classes transparently.  The SCCP protocol
  classes are defined as follows:





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  *  Protocol class 0 provides unordered transfer of SCCP-user messages
     in a connectionless manner.

  *  Protocol class 1 allows the SCCP-user to select the sequenced
     delivery of SCCP-user messages in a connectionless manner.

  *  Protocol class 2 allows the bidirectional transfer of SCCP-user
     messages by setting up a temporary or permanent signalling
     connection.

  *  Protocol class 3 allows the features of protocol class 2 with the
     inclusion of flow control.  Detection of message loss or mis-
     sequencing is included.

  Protocol classes 0 and 1 make up the SCCP connectionless service.
  Protocol classes 2 and 3 make up the SCCP connection-oriented
  service.

1.4.3.  Native Management Functions

  The SUA layer provides the capability to indicate errors associated
  with the SUA-protocol messages and to provide notification to local
  management and the remote peer as is necessary.

1.4.4.  Interworking with SCCP Network Management Functions

  SUA uses the existing ASP management messages for ASP status
  handling.  The interworking with SCCP management messages consists of
  DUNA, DAVA, DAUD, DRST, DUPU or SCON messages (defined in section 3)
  on receipt of SSP, SSA, SST or SSC (defined by SCCP) to the
  appropriate ASPs.  See also chapter 1.4.5.  The primitives below are
  sent between the SCCP and SUA management functions in the SG to
  trigger events in the IP and SS7 domain.

  Generic   |Specific   |
  Name      |Name       |ANSI/ITU Reference
  ----------+-----------+---------------------------------------------
  N-State   |Request    |ITU-Q.711   Chap 6.3.2.3.2 (Tab 16/Q.711)
            |Indication |ANSI-T1.112 Chap 2.3.2.3.2 (Tab 8E/T1.112.1)
  ----------+-----------+---------------------------------------------
  N-PCstate |Indication |ITU-Q.711   Chap 6.3.2.3.3 (Tab 1/Q.711)
            |           |ANSI-T1.112 Chap 2.3.2.3.4 (Tab 8G/T1.112.1)
  ----------+-----------+---------------------------------------------
  N-Coord   |Request    |ITU-Q.711   Chap 6.3.2.3.1 (Tab 15/Q.711)
            |Indication |ANSI-T1.112 Chap 2.3.2.3.3 (Tab 8F/T1.112.1)
            |Response   |
            |Confirm    |




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1.4.5.  Support for the management between the SGP and ASP.

  The SUA layer provides interworking with SCCP management functions at
  the SG for operation between the switched circuit networks and the IP
  network.  It should:

  *  Provide an indication to the SCCP-user at an ASP that a SS7
     endpoint/peer is unreachable.
  *  Provide an indication to the SCCP-user at an ASP that a SS7
     endpoint/peer is reachable.
  *  Provide congestion indication to SCCP-user at an ASP.
  *  Provide the initiation of an audit of SS7 endpoints at the SG.

1.4.6.  Relay function

  For network scalability purposes, the SUA may be enhanced with a
  relay functionality to determine the next hop SCTP association toward
  the destination SUA endpoint.

  The determination of the next hop may be based on Global Title
  information (e.g., E.164 number), in analogy with SCCP GTT in SS7
  networks, modeled in [ITU-T Q.714].  It may also be based on Hostname
  information, IP address or pointcode contained in the called party
  address.

  This allows for greater scalability, reliability and flexibility in
  wide-scale deployments of SUA.  The usage of a relay function is a
  deployment decision.

1.5.  Internal Functions Provided in the SUA Layer

  To perform its addressing and relaying capabilities, the SUA makes
  use of an Address Mapping Function (AMF).  This function is
  considered part of SUA, but the way it is realized is left
  implementation / deployment dependent (local tables, DNS [3761],
  LDAP, etc.)

  The AMF is invoked when a message is received at the incoming
  interface.  The AMF is responsible for resolving the address
  presented in the incoming SCCP/SUA message to SCTP associations to
  destinations within the IP network.  The AMF will select the
  appropriate SCTP association based upon routing context / routing key
  information available.  The destination might be the end SUA node or
  a SUA relay node.  The Routing Keys reference an Application Server,
  which will have one or more ASPs processing traffic for the AS.  The
  availability and status of the ASPs is handled by SUA ASP management
  messages.




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RFC 3868                          SUA                       October 2004


  Possible SS7 address/routing information that comprise a Routing Key
  entry includes, for example, OPC, DPC, SIO found in the MTP3 routing
  label, SCCP subsystem number, or Transaction ID.  IP addresses and
  hostnames can also be used as Routing Key Information.

  It is expected that the routing keys be provisioned via a MIB,
  dynamic registration or external process, such as a database.

1.5.1.  Address Mapping at the SG

  Normally, one or more ASPs are active in the AS (i.e., currently
  processing traffic) but in certain failure and transition cases it is
  possible that there may not be an active ASP available.  The SGP will
  buffer the message destined for this AS for a time T(r) or until an
  ASP becomes available.  When no ASP becomes available before expiry
  of T(r), the SGP will flush the buffered messages and initiate the
  appropriate return or refusal procedures.

  If there is no address mapping match for an incoming message, a
  default treatment MAY be specified.  Possible solutions are to
  provide a default Application Server to direct all unallocated
  traffic to a (set of) default ASP(s), or to drop the messages and
  provide a notification to management.  The treatment of unallocated
  traffic is implementation dependent.

1.5.2.  Address Mapping at the ASP

  To direct messages to the SS7 network, the ASP MAY perform an address
  mapping to choose the proper SGP for a given message.  This is
  accomplished by observing the Destination Point Code and other
  elements of the outgoing message, SS7 network status, SGP
  availability, and Routing Context configuration tables.

  A Signalling Gateway may be composed of one or more SGPs.  There is,
  however, no SUA messaging to manage the status of an SGP.  Whenever
  an SCTP association to an SGP exists, it is assumed to be available.
  Also, every SGP of one SG communicating with one ASP regarding one AS
  provides identical SS7 connectivity to this ASP.

  An ASP routes responses to the SGP that it received messages from;
  within the routing context which it is currently active and receiving
  traffic.

1.5.3.  Address Mapping Function at a Relay Node

  The relay function is invoked when:

  -  Routing is on Global Title



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RFC 3868                          SUA                       October 2004


  -  Routing is on Hostname
  -  Routing is on SSN and PC or SSN and IP Address and the address
     presented is not the one of the relay node

  Translation/resolution of the above address information yields one of
  the following:

  -  Route on SSN: SCTP association ID toward the destination node, SSN
     and optionally Routing Context and/or IP address.
  -  Route on GT: SCTP association ID toward next relay node, (new) GT
     and optionally SSN and/or Routing Context.
  -  Routing on Hostname: SCTP association ID toward next relay node,
     (new) Hostname and optionally SSN and/or Routing Context.
  -  A local SUA-user (combined relay/end node)

  To prevent looping, an SS7 hop counter is used.  The originating end
  node (be it an SS7 or an IP node) sets the value of the SS7 hop
  counter to the maximum value (15 or less).  Each time the relay
  function is invoked within an intermediate (relay) node, the SS7 hop
  counter is decremented.  When the value reaches zero, the return or
  refusal procedures are invoked with reason "Hop counter violation".

1.5.4.  SCTP Stream Mapping

  The SUA supports SCTP streams.  Signalling Gateway SG and Application
  Servers need to maintain a list of SCTP and SUA-users for mapping
  purposes.  SCCP-users requiring sequenced message transfer need to be
  sent over a stream with sequenced delivery.

  SUA uses stream 0 for SUA management messages.  It is OPTIONAL that
  sequenced delivery be used to preserve the order of management
  message delivery.

  Stream selection based on protocol class:

  -  Protocol class 0: SUA MAY select unordered delivery.  The stream
     selected is based on traffic information available to the SGP or
     ASP.

  -  Protocol class 1: SUA MUST select ordered delivery.  The stream
     selected is based upon the sequence parameter given by the upper
     layer over the primitive interface and other traffic information
     available to the SGP or ASP

  -  Protocol classes 2 and 3: SUA MUST select ordered delivery. The
     stream selected is based upon the source local reference of the
     connection and other traffic information available to the SGP or
     ASP.



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RFC 3868                          SUA                       October 2004


1.5.5.  Flow Control

  Local Management at an ASP may wish to stop traffic across an SCTP
  association to temporarily remove the association from service or to
  perform testing and maintenance activity.  The function could
  optionally be used to control the start of traffic on to a newly
  available SCTP association.

1.5.6.  Congestion Management

  The SUA layer is informed of local and IP network congestion by means
  of an implementation-dependent function (e.g., an implementation-
  dependent indication from the SCTP of IP network congestion).

  At an ASP or IPSP, the SUA layer indicates congestion to local SCCP-
  Users by means of an appropriate SCCP primitive (e.g., N-INFORM, N-
  NOTICE), as per current SCCP procedures, to invoke appropriate upper
  layer responses.  When an SG determines that the transport of SS7
  messages is encountering congestion, the SG MAY trigger SS7 SCCP
  Congestion messages to originating SS7 nodes, per the congestion
  procedures of the relevant SCCP standard.  The triggering of SS7 SCCP
  Management messages from an SG is an implementation-dependent
  function.

  The SUA layer at an ASP or IPSP MAY indicate local congestion to an
  SUA peer with an SCON message.  When an SG receives a congestion
  message (SCON) from an ASP, and the SG determines that an endpoint is
  now encountering congestion, it MAY trigger congestion procedures of
  the relevant SCCP standard.

1.6.  Definition of SUA Boundaries

1.6.1.  Definition of the upper boundary

  The following primitives are supported between the SUA and an SCCP-
  user (a reference to ITU and ANSI sections where these primitives and
  corresponding parameters are described, is also given):

  Generic     |Specific  |
  Name        |Name      |ANSI/ITU Reference
  ------------+----------+-------------------------------------------
  N-CONNECT   |Request   |ITU-Q.711   Chap 6.1.1.2.2 (Tab 2/Q.711)
              |Indication|ANSI-T1.112 Chap 2.1.1.2.2 (Tab 2/T1.112.1)
              |Response  |
              |Confirm   |
  ------------+----------+-------------------------------------------
  N-DATA      |Request   |ITU-Q.711   Chap 6.1.1.2.3 (Tab 3/Q.711)
              |Indication|ANSI-T1.112 Chap 2.1.1.2.3 (Tab 3/T1.112.1)



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RFC 3868                          SUA                       October 2004


  ------------+----------+-------------------------------------------
  N-EXPEDITED |Request   |ITU-Q.711   Chap 6.1.1.2.3 (Tab 4/Q.711)
  DATA        |Indication|ANSI-T1.112 Chap 2.1.1.2.3 (Tab 4/T1.112.1)
  ------------+----------+-------------------------------------------
  N-RESET     |Request   |ITU-Q.711   Chap 6.1.1.2.3 (Tab 5/Q.711)
              |Indication|ANSI-T1.112 Chap 2.1.1.2.3 (Tab 5/T1.112.1)
              |Response  |
              |Confirm   |
  ------------+----------+-------------------------------------------
  N-DISCONNECT|Request   |ITU-Q.711   Chap 6.1.1.2.4 (Tab 6/Q.711)
              |Indication|ANSI-T1.112 Chap 2.1.1.2.4 (Tab 6/T1.112.1)
  ------------+----------+-------------------------------------------
  N-INFORM    |Request   |ITU-Q.711   Chap 6.1.1.3.2 (Tab 8/Q.711)
              |Indication|ANSI-T1.112 Chap 2.1.1.2.5 (Tab 6A/T1.112.1)
  ------------+----------+-------------------------------------------
  N-UNITDATA  |Request   |ITU-Q.711   Chap 6.2.2.3.1 (Tab 12/Q.711)
              |Indication|ANSI-T1.112 Chap 2.2.2.3.1 (Tab 8A/T1.112.1)
  ------------+----------+-------------------------------------------
  N-NOTICE    |Indication|ITU-Q.711   Chap 6.2.2.3.2 (Tab 13/Q.711)
              |          |ANSI-T1.112 Chap 2.2.2.3.2 (Tab 8B/T1.112.1)
  ------------+----------+--------------------------------------------
  N-STATE     |Request   |ITU-Q.711   Chap 6.3.2.3.2 (Tab 16/Q.711)
              |Indication|ANSI-T1.112 Chap 2.3.2.3.2 (Tab 8E/T1.112.1)
  ------------+----------+--------------------------------------------
  N-PCSTATE   |Indication|ITU-Q.711   Chap 6.3.2.3.3 (Tab 17/Q.711)
              |          |ANSI-T1.112 Chap 2.3.2.3.4 (Tab 8G/T1.112.1)
  ------------+----------+--------------------------------------------
  N-COORD     |Request   |ITU-Q.711   Chap 6.3.2.3.1 (Tab 15/Q.711)
              |Indication|ANSI-T1.112 Chap 2.3.2.3.3 (Tab 8F/T1.112.1)
              |Response  |
              |Confirm   |

1.6.2.  Definition of the lower boundary

  The upper layer primitives provided by the SCTP are provided in
  [SCTP].

1.6.3.  Definition of the Boundary between SUA and Layer Management

  M-SCTP_ESTABLISH request
  Direction: LM -> SUA
  Purpose:  LM requests ASP to establish an SCTP association with its
            peer.

  M-SCTP_ESTABLISH confirm
  Direction: SUA -> LM
  Purpose:  ASP confirms to LM that it has established an SCTP
            association with its peer.



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RFC 3868                          SUA                       October 2004



  M-SCTP_ESTABLISH indication
  Direction: SUA -> LM
  Purpose:  SUA informs LM that a remote ASP has established an SCTP
            association.

  M-SCTP_RELEASE request
  Direction: LM -> SUA
  Purpose:  LM requests ASP to release an SCTP association with its
            peer.

  M-SCTP_RELEASE confirm
  Direction: SUA -> LM
  Purpose:  ASP confirms to LM that it has released SCTP association
            with its peer.

  M-SCTP_RELEASE indication
  Direction: SUA -> LM
  Purpose:  SUA informs LM that a remote ASP has released an SCTP
            Association or the SCTP association has failed.

  M-SCTP RESTART indication
  Direction: SUA -> LM
  Purpose:  SUA informs LM that an SCTP restart indication has been
            received.

  M-SCTP_STATUS request
  Direction: LM -> SUA
  Purpose:  LM requests SUA to report the status of an SCTP
            association.

  M-SCTP_STATUS confirm
  Direction: SUA -> LM
  Purpose:  SUA responds with the status of an SCTP association.

  M-SCTP STATUS indication
  Direction: SUA -> LM
  Purpose:  SUA reports the status of an SCTP association.

  M-ASP_STATUS request
  Direction: LM -> SUA
  Purpose:  LM requests SUA to report the status of a local or remote
              ASP.

  M-ASP_STATUS confirm
  Direction: SUA -> LM
  Purpose:  SUA reports status of local or remote ASP.




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  M-AS_STATUS request
  Direction: LM -> SUA
  Purpose:  LM requests SUA to report the status of an AS.

  M-AS_STATUS confirm
  Direction: SUA -> LM
  Purpose:  SUA reports the status of an AS.

  M-NOTIFY indication
  Direction: SUA -> LM
  Purpose:  SUA reports that it has received a Notify message from its
            peer.

  M-ERROR indication
  Direction: SUA -> LM
  Purpose:  SUA reports that it has received an Error message from its
            peer or that a local operation has been unsuccessful.

  M-ASP_UP request
  Direction: LM -> SUA
  Purpose:  LM requests ASP to start its operation and send an ASP Up
            message to its peer.

  M-ASP_UP confirm
  Direction: SUA -> LM
  Purpose:  ASP reports that is has received an ASP UP Ack message
            from its peer.

  M-ASP_UP indication
  Direction: SUA -> LM
  Purpose:  SUA reports it has successfully processed an incoming ASP
            Up message from its peer.

  M-ASP_DOWN request
  Direction: LM -> SUA
  Purpose:  LM requests ASP to stop its operation and send an ASP Down
            message to its peer.

  M-ASP_DOWN confirm
  Direction: SUA -> LM
  Purpose:  ASP reports that is has received an ASP Down Ack message
            from its peer.

  M-ASP_DOWN indication
  Direction: SUA -> LM
  Purpose:  SUA reports it has successfully processed an incoming ASP
            Down message from its peer, or the SCTP association has
            been lost/reset.



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RFC 3868                          SUA                       October 2004



  M-ASP_ACTIVE request
  Direction: LM -> SUA
  Purpose:  LM requests ASP to send an ASP Active message to its peer.

  M-ASP_ACTIVE confirm
  Direction: SUA -> LM
  Purpose:  ASP reports that is has received an ASP Active Ack message
            from its peer.

  M-ASP_ACTIVE indication
  Direction: SUA -> LM
  Purpose:  SUA reports it has successfully processed an incoming ASP
            Active message from its peer.

  M-ASP_INACTIVE request
  Direction: LM -> SUA
  Purpose:  LM requests ASP to send an ASP Inactive message to its
            peer.

  M-ASP_INACTIVE confirm
  Direction: LM -> SUA
  Purpose:  ASP reports that is has received an ASP Inactive
            Ack message from its peer.

  M-ASP_INACTIVE indication
  Direction: SUA -> LM
  Purpose:  SUA reports it has successfully processed an incoming ASP
            Inactive message from its peer.

  M-AS_ACTIVE indication
  Direction: SUA -> LM
  Purpose:  SUA reports that an AS has moved to the AS-ACTIVE state.

  M-AS_INACTIVE indication
  Direction: SUA -> LM
  Purpose: SUA reports that an AS has moved to the AS-INACTIVE state.

  M-AS_DOWN indication
  Direction: SUA -> LM
  Purpose: SUA reports that an AS has moved to the AS-DOWN state.










Loughney, et al.            Standards Track                    [Page 18]

RFC 3868                          SUA                       October 2004


  If the SUA layer supports dynamic registration of Routing Key, the
  layer MAY support the following additional primitives:

  M-RK_REG request
  Direction: LM -> SUA
  Purpose:  LM requests ASP to register RK(s) with its peer by sending
            REG REQ message.

  M-RK_REG confirm
  Direction: SUA -> LM
  Purpose:  ASP reports that it has received REG RSP message with
            registration status as successful from its peer.

  M-RK_REG indication
  Direction: SUA -> LM
  Purpose:  SUA informs LM that it has successfully processed an
            incoming REG REQ message.

  M-RK_DEREG request
  Direction: LM -> SUA
  Purpose:  LM requests ASP to deregister RK(s) with its peer by
            sending DEREG REQ message.

  M-RK_DEREG confirm
  Direction: SUA -> LM
  Purpose:  ASP reports that it has received DEREG RESP message with
            deregistration status as successful from its peer.

  M-RK_DEREG indication
  Direction: SUA -> LM
  Purpose:  SUA informs LM that it has successfully processed an
            incoming DEREG REQ from its peer.

2.  Conventions

  The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
  SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
  they appear in this document, are to be interpreted as described in
  BCP 14, RFC 2119 [2119].

3.  Protocol Elements

  The general message format includes a Common Message Header together
  with a list of zero or more parameters as defined by the Message
  Type.

  For forward compatibility, all Message Types may have attached
  parameters even if none are specified in this version.



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RFC 3868                          SUA                       October 2004


  The Reserved field is set to 0 in messages sent and is not to be
  examined in messages received.

3.1.  Common Message Header

  The protocol messages for the SCCP-User Adaptation Protocol requires
  a message structure which contains a version, message class, message
  type, message length and message contents.  This message header is
  common among all signalling protocol adaptation layers:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    Version    |   Reserved    | Message Class | Message Type  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Message Length                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Message Data                          |

  Note that the 'data' portion of SUA messages SHALL contain SCCP-User
  data, not the encapsulated SCCP message.

  Optional parameters can only occur at most once in an SUA message.

3.1.1.  SUA Protocol Version

  The version field (ver) contains the version of the SUA adaptation
  layer.  The supported versions are:

     1   SUA version 1.0

3.1.2.  Message Classes

  Message Classes

     0         SUA Management (MGMT) Message
     1         Reserved
     2         Signalling Network Management (SNM) Messages
     3         ASP State Maintenance (ASPSM) Messages
     4         ASP Traffic Maintenance (ASPTM) Messages
     5         Reserved
     6         Reserved
     7         Connectionless Messages
     8         Connection-Oriented Messages
     9         Routing Key Management (RKM) Messages.
     10 - 127  Reserved by the IETF
     128 - 255 Reserved for IETF-Defined Message Class Extensions




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RFC 3868                          SUA                       October 2004


3.1.3.  Message Types

  SUA Management Messages

     0         Error (ERR)
     1         Notify (NTFY)
     2 - 127   Reserved by the IETF
     128- 255  Reserved for IETF-Defined Message Class Extensions

  Signalling Network Management (SNM) Messages

     0         Reserved
     1         Destination Unavailable (DUNA)
     2         Destination Available (DAVA)
     3         Destination State Audit (DAUD)
     4         Signalling Congestion (SCON)
     5         Destination User Part Unavailable (DUPU)
     6         Destination Restricted (DRST)
     7 - 127   Reserved by the IETF
     128 - 255 Reserved for IETF-Defined Message Class Extensions

  Application Server Process State Maintenance (ASPSM) Messages

     0         Reserved
     1         ASP Up (UP)
     2         ASP Down (DOWN)
     3         Heartbeat (BEAT)
     4         ASP Up Ack (UP ACK)
     5         ASP Down Ack (DOWN ACK)
     6         Heartbeat Ack (BEAT ACK)
     7 - 127   Reserved by the IETF
     128 - 255 Reserved for IETF-Defined Message Class Extensions

  ASP Traffic Maintenance (ASPTM) Messages

     0         Reserved
     1         ASP Active (ACTIVE)
     2         ASP Inactive (INACTIVE)
     3         ASP Active Ack (ACTIVE ACK)
     4         ASP Inactive Ack (INACTIVE ACK)
     5 - 127   Reserved by the IETF
     128 - 255 Reserved for IETF-Defined Message Class Extensions









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RFC 3868                          SUA                       October 2004


  Routing Key Management (RKM) Messages

     0         Reserved
     1         Registration Request (REG REQ)
     2         Registration Response (REG RSP)
     3         Deregistration Request (DEREG REQ)
     4         Deregistration Response (DEREG RSP)
     5 - 127   Reserved by the IETF
     128 - 255 Reserved for IETF-Defined Message Class Extensions

  Connectionless (CL) Messages

     0         Reserved
     1         Connectionless Data Transfer (CLDT)
     2         Connectionless Data Response (CLDR)
     3 - 127   Reserved by the IETF
     128 - 255 Reserved for IETF-Defined Message Class Extensions

  Connection-Oriented (CO) Messages

     0         Reserved
     1         Connection Request (CORE)
     2         Connection Acknowledge (COAK)
     3         Connection Refused (COREF)
     4         Release Request (RELRE)
     5         Release Complete (RELCO)
     6         Reset Confirm (RESCO)
     7         Reset Request (RESRE)
     8         Connection Oriented Data Transfer (CODT)
     9         Connection Oriented Data Acknowledge (CODA)
     10        Connection Oriented Error (COERR)
     11        Inactivity Test (COIT)
     12 - 127  Reserved by the IETF
     128 - 255 Reserved for IETF-Defined Message Class Extensions

3.1.4.  Message Length

  The Message Length defines the length of the message in octets,
  including the header and including all padding bytes.  Message Length
  is a 32-bit identifier.

3.1.5.  Tag-Length-Value Format

  SUA messages consist of a Common Header followed by zero or more
  parameters, as defined by the message type.  The Tag-Length-Value
  (TLV) parameters contained in a message are defined in a Tag-Length-
  Value format as shown below.




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RFC 3868                          SUA                       October 2004


   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Parameter Tag        |       Parameter Length        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  \                                                               \
  /                       Parameter Value                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameter Tag: 16 bits (unsigned integer)

     Tag field is a 16-bit identifier of the type of parameter.  It
     takes a value of 0 to 65535.

  Parameter Length: 16 bits (unsigned integer)

     The Parameter Length field contains the size of the parameter in
     bytes, including the Parameter Tag, Parameter Length, and
     Parameter Value fields.  The Parameter Length does not include any
     padding bytes.  However, composite parameters will contain all
     padding bytes, since all parameters contained within this
     composite parameter will be considered multiples of 4 bytes.

  Parameter Value: variable-length.

     The Parameter Value field contains the actual information to be
     transfered in the parameter.

     The total length of a parameter (including Tag, Parameter Length
     and Value fields) MUST be a multiple of 4 bytes.  If the length of
     the parameter is not a multiple of 4 bytes, the sender pads the
     parameter at the end (i.e., after the Parameter Value field) with
     all zero bytes.  The length of the padding is NOT included in the
     parameter length field.  A sender SHOULD NOT pad with more than 3
     bytes.  The receiver MUST ignore the padding bytes.

  Implementation note: The use of TLV in principle allows the
  parameters to be placed in a random order in the message.  However,
  some guidelines should be considered for easy processing in the
  following order:

  -  Parameters needed to correctly process other message parameters,
     preferably should precede these parameters (such as Routing
     Context).
  -  Mandatory parameters preferably SHOULD precede any optional
     parameters.
  -  The data parameter will normally be the final one in the message.



Loughney, et al.            Standards Track                    [Page 23]

RFC 3868                          SUA                       October 2004


  -  The receiver SHOULD accept parameters in any order, except where
     explicitly mandated.

3.2.  SUA Connectionless Messages

  The following section describes the SUA Connectionless transfer
  messages and parameter contents.  The general message format includes
  a Common Message Header together with a list of zero or more
  parameters as defined by the Message Type.  All Message Types can
  have attached parameters.

3.2.1.  Connectionless Data Transfer (CLDT)

  This message transfers data between one SUA to another.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0006         |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0115          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                         Protocol Class                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0102          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                        Source Address                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0103          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                     Destination Address                       /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0116         |             Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        Sequence Control                       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0101          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                         SS7 Hop Count                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0113          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          Importance                           |



Loughney, et al.            Standards Track                    [Page 24]

RFC 3868                          SUA                       October 2004


  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0114          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                      Message Priority                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0013          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                         Correlation ID                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0117          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          Segmentation                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010B          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                             Data                              /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Mandatory
    Protocol Class                Mandatory
    Source Address                Mandatory
    Destination Address           Mandatory
    Sequence Control              Mandatory
    SS7 Hop Count                 Optional
    Importance                    Optional
    Message Priority              Optional
    Correlation ID                Optional
    Segmentation                  Optional
    Data                          Mandatory

  Implementation note: This message covers the following SCCP messages:
  unitdata (UDT), extended unitdata (XUDT), long unitdata (LUDT).

3.2.2.  Connectionless Data Response (CLDR)

  This message is used as a response message by the peer to report
  errors in the received CLDT message, when the return on error option
  is set.











Loughney, et al.            Standards Track                    [Page 25]

RFC 3868                          SUA                       October 2004


   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0006         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0106          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                           SCCP Cause                          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0102          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                        Source Address                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0103          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                     Destination Address                       /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0101          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                         SS7 Hop Count                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0113          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          Importance                           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0114          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                      Message Priority                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0013          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                         Correlation ID                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0117          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          Segmentation                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010b          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
  /                             Data                              /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




Loughney, et al.            Standards Track                    [Page 26]

RFC 3868                          SUA                       October 2004


  Parameters
    Routing Context               Mandatory
    SCCP Cause                    Mandatory
    Source Address                Mandatory
    Destination Address           Mandatory
    SS7 Hop Count                 Optional
    Importance                    Optional
    Message Priority              Optional
    Correlation ID                Optional
    Segmentation                  Optional
    Data                          Optional

  Implementation note: This message covers the following SCCP messages:
  unitdata service (UDTS), extended unitdata service (XUDTS) and long
  unitdata service (LUDTS).

3.3.  Connection Oriented Messages

3.3.1.  Connection Oriented Data Transfer (CODT)

  This message transfers data between one SUA to another for
  connection-oriented service.





























Loughney, et al.            Standards Track                    [Page 27]

RFC 3868                          SUA                       October 2004


   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0006         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0107          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        Sequence Number                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0105          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Destination Reference Number                  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0114          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                      Message Priority                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0013          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        Correlation ID                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010b          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                             Data                              /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Mandatory
    Sequence Number               Optional *1
    Destination Reference Number  Mandatory
    Message Priority              Optional
    Correlation ID                Optional
    Data                          Mandatory

  NOTE *1:   This parameter is not present in case of Expedited Data
             (ED).

  Implementation note: For the CODT to represent DT1, DT2 and ED
  messages, the following conditions MUST be met:

  DT1 is represented by a CODT when:
    Sequence Number parameter is present (contains "more" indicator).





Loughney, et al.            Standards Track                    [Page 28]

RFC 3868                          SUA                       October 2004


  DT2 is represented by a CODT when:
    Sequence Number parameter is present (contains P(S), P(R) and more
    indicator)

  ED is represented by a CODT with:
    Sequence Number parameter is not present

3.3.2.  Connection Oriented Data Acknowledge (CODA)

  The peer uses this message to acknowledge receipt of data.  This
  message is used only with protocol class 3.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0006         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0105          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Destination Reference Number                  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0108          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                   Receive Sequence Number                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010A          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                            Credit                             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Mandatory
    Destination Reference Number  Mandatory
    Receive Sequence Number       Optional *1
    Credit                        Mandatory *1

  NOTE *1:    Mandatory when representing Data Acknowledgement (AK).

  Implementation note: For the CODA to represent DA and EA messages,
  the following conditions MUST be met:

  DA is represented by a CODA when:
    Receive Sequence Number parameter is present (contains P(S), P(R)
    and more indicator)




Loughney, et al.            Standards Track                    [Page 29]

RFC 3868                          SUA                       October 2004


  EA is represented by a CODA when:
    Receive Sequence Number parameter is not present

3.3.3.  Connection Request (CORE)

  This message is used for establishing a signalling connection between
  two peer endpoints.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0006         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0115          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                         Protocol Class                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0104          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                   Source Reference Number                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0103          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                     Destination Address                       /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0116          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        Sequence Control                       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0107          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        Sequence Number                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0102          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                        Source Address                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0101          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                         SS7 Hop Count                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0113          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



Loughney, et al.            Standards Track                    [Page 30]

RFC 3868                          SUA                       October 2004


  |                          Importance                           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0114          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                      Message Priority                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010A          |           Length              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                            Credit                             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010b          |           Length              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                             Data                              /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Mandatory
    Protocol Class                Mandatory
    Source Reference Number       Mandatory
    Destination Address           Mandatory
    Sequence Control              Mandatory
    Sequence Number               Optional *1
    Source Address                Optional
    SS7 Hop Count                 Optional
    Importance                    Optional
    Message Priority              Optional
    Credit                        Optional *1
    Data                          Optional

  NOTE *1:    Mandatory for protocol class 3 only.

  Implementation note: This message covers the following SCCP message:
  Connection Request (CR).

















Loughney, et al.            Standards Track                    [Page 31]

RFC 3868                          SUA                       October 2004


3.3.4.  Connection Acknowledge (COAK)

  This message is used to acknowledge a connection request from the
  peer endpoint.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0006         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0115          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                         Protocol Class                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0105          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Destination Reference Number                  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0104          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                   Source Reference Number                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x01116          |            Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        Sequence Control                       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010A          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                            Credit                             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0102          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                        Source Address                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0113          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          Importance                           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0114          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                      Message Priority                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0103          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



Loughney, et al.            Standards Track                    [Page 32]

RFC 3868                          SUA                       October 2004


  /                     Destination Address                       /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010b          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                             Data                              /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Mandatory
    Protocol Class                Mandatory
    Destination Reference Number  Mandatory
    Source Reference Number       Mandatory
    Sequence Control              Mandatory
    Credit                        Mandatory *2
    Source Address                Optional
    Importance                    Optional
    Message Priority              Optional
    Destination Address           Optional *1
    Data                          Optional

  NOTE *1:    Destination Address parameter will be present in case
              that the received CORE message conveys the Source
              Address parameter.

  NOTE *2:    Only applicable for protocol class 3.

  Implementation note: This message covers the following SCCP message:
  Connection Confirm (CC).





















Loughney, et al.            Standards Track                    [Page 33]

RFC 3868                          SUA                       October 2004


3.3.5.  Connection Refused (COREF)

  This message is used to refuse a connection request between two peer
  endpoints.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0006         |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0105          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Destination Reference Number                  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0106          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                           SCCP Cause                          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0102          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                        Source Address                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0103          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                     Destination Address                       /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0113          |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          Importance                           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010B          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                             Data                              /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+











Loughney, et al.            Standards Track                    [Page 34]

RFC 3868                          SUA                       October 2004


  Parameters
    Routing Context                    Mandatory
    Destination Reference Number       Mandatory
    SCCP Cause                         Mandatory
    Source Address                     Optional
    Destination Address                Optional *1
    Importance                         Optional
    Data                               Optional

  Note *1:    Destination Address parameter will be present in case
              that the received CORE message conveys the Source Address
              parameter.

  Implementation note: This message covers the following SCCP message:
  Connection REFused (CREF).




































Loughney, et al.            Standards Track                    [Page 35]

RFC 3868                          SUA                       October 2004


3.3.6.  Release Request (RELRE)

  This message is used to request a signalling connection between two
  peer endpoints be released.  All associated resources can then be
  released.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0006         |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0105          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Destination Reference Number                  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0104          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                   Source Reference Number                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0106          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          SCCP Cause                           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0113          |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          Importance                           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010b          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                             Data                              /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Mandatory
    Destination Reference Number  Mandatory
    Source Reference Number       Mandatory
    SCCP Cause                    Mandatory
    Importance                    Optional
    Data                          Optional

  Implementation note: This message covers the following SCCP message:
  connection ReLeaSeD (RLSD).





Loughney, et al.            Standards Track                    [Page 36]

RFC 3868                          SUA                       October 2004


3.3.7.  Release Complete (RELCO)

  This message is used to acknowledge the release of a signalling
  connection between two peer endpoints.  All associated resources
  should be released.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0006         |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0105          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Destination Reference Number                  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0104          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                   Source Reference Number                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0113          |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          Importance                           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Mandatory
    Destination Reference Number  Mandatory
    Source Reference Number       Mandatory
    Importance                    Optional

  Implementation note: This message covers the following SCCP message:
  ReLease Complete (RLC).
















Loughney, et al.            Standards Track                    [Page 37]

RFC 3868                          SUA                       October 2004


3.3.8.  Reset Request (RESRE)

  This message is used to indicate that the sending SCCP/SUA wants to
  initiate a reset procedure (reinitialization of sequence numbers) to
  the peer endpoint.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0006         |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0105          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Destination Reference Number                  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0104          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                     Source Reference Number                   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0106          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                           SCCP Cause                          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Mandatory
    Destination Reference Number  Mandatory
    Source Reference Number       Mandatory
    SCCP Cause                    Mandatory

  Implementation note: This message covers the following SCCP message:
  ReSet Request (RSR).
















Loughney, et al.            Standards Track                    [Page 38]

RFC 3868                          SUA                       October 2004


3.3.9.  Reset Confirm (RESCO)

  This message is used to confirm the Reset Request.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0006         |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0105          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Destination Reference Number                  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0104          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                   Source Reference Number                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Mandatory
    Destination Reference Number  Mandatory
    Source Reference Number       Mandatory

  Implementation note: This message covers the following SCCP message:
  ReSet Confirmation (RSC).























Loughney, et al.            Standards Track                    [Page 39]

RFC 3868                          SUA                       October 2004


3.3.10.  Connection Oriented Error (COERR)

  The COERR message is sent to indicate a protocol data unit error.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0006          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0105          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Destination Reference Number                  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0106          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          SCCP Cause                           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Mandatory
    Destination Reference Number  Mandatory
    SCCP Cause                    Mandatory

  Implementation note: This message covers the following SCCP message:
  Protocol Data Unit ERRor (ERR).























Loughney, et al.            Standards Track                    [Page 40]

RFC 3868                          SUA                       October 2004


3.3.11.  Connection Oriented Inactivity Test (COIT)

  This message is used for auditing the signalling connection state and
  the consistency of connection data at both ends of the signalling
  connection.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0006          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0115          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                         Protocol Class                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0104          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                   Source Reference Number                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0105          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Destination Reference number                  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0107          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        Sequence number                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010A          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                            Credit                             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Mandatory
    Protocol Class                Mandatory
    Source Reference Number       Mandatory
    Destination Reference number  Mandatory
    Sequence Number               Mandatory *1
    Credit                        Mandatory *1

  NOTE *1:    Information in these parameter fields reflects those
              values sent in the last data form 2 or data
              acknowledgement message.  They are ignored if the
              protocol class indicates class 2.




Loughney, et al.            Standards Track                    [Page 41]

RFC 3868                          SUA                       October 2004


  Implementation note: This message covers the following SCCP message:
  Inactivity Test (IT).

3.4.  Signalling Network Management (SNM) Messages

3.4.1.  Destination Unavailable (DUNA)

  In the scope of SUA, this message is covered by the PC- or N-state
  indication passed between SCCP and local SCCP-user.  The DUNA message
  is sent from the SG or relay node to all concerned ASPs (servicing
  SCCP-users considered local to the SG or relay node, see chapter
  1.3.1.1), when a destination or SCCP-user has become unreachable. The
  SUA-User at the ASP is expected to stop traffic to the affected
  destination or SCCP-user through the SG or relay node initiating the
  DUNA.

  The format for DUNA Message parameters is as follows:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0006          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0012          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                        Affected Point Code                    /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x8003          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                              SSN                              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0112          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                              SMI                              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0004          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                          Info String                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+







Loughney, et al.            Standards Track                    [Page 42]

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  Parameters
    Routing Context               Optional
    Affected Point Code           Mandatory *1
    SSN                           Optional *1
    SMI                           Optional
    Info String                   Optional

  Note 1:    When the SSN is included, the DUNA message
             corresponds to the SCCP N-STATE primitive.  When SSN
             is not, the DUNA message corresponds to the SCCP N-PCSTATE
             primitive.  The Affected Point Code parameter can only
             contain one point code when SSN is present.

3.4.2.  Destination Available (DAVA)

  In the scope of SUA, this message is covered by the PC- and N-state
  indication passed between SCCP and local SCCP-user.  The DAVA message
  is sent from the SG or relay node to all concerned ASPs (servicing
  SCCP-users considered local to the SG or relay node, see chapter
  1.3.1.1) to indicate that a destination (PC or SCCP-user) is now
  reachable.  The ASP SUA-User protocol is expected to resume traffic
  to the affected destination through the SG or relay node initiating
  the DAVA.




























Loughney, et al.            Standards Track                    [Page 43]

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   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0006          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0012          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                        Affected Point Code                    /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x8003          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                              SSN                              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0112          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                              SMI                              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0004          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                          Info String                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Optional
    Affected Point Code           Mandatory *1
    SSN                           Optional *1
    SMI                           Optional
    Info String                   Optional

  Note 1:    When the SSN is included, the DAVA message corresponds to
             the SCCP N-STATE primitive.  When SSN is not included, the
             DAVA message corresponds to the SCCP N-PCSTATE primitive.
             The Affected Point Code can only contain one point code
             when SSN is present.

3.4.3.  Destination State Audit (DAUD)

  The DAUD message can be sent from the ASP to the SG (or relay node)
  to query the availability state of the routes to an affected
  destination.  A DAUD may be sent periodically after the ASP has
  received a DUNA, until a DAVA is received.  The DAUD can also be sent
  when an ASP recovers from isolation from the SG (or relay node).




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RFC 3868                          SUA                       October 2004


   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0006          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0012          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                        Affected Point Code                    /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x8003          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                              SSN                              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010C          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                           User/Cause                          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0004          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                          Info String                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Optional
    Affected Point Code           Mandatory *1
    SSN                           Optional *1
    User / Cause                  Optional
    Info String                   Optional

  Note 1:    If the SSN is present, the DAUD is "soliciting" N-STATE
             primitives, otherwise it is "soliciting" N-PCSTATE
             primitives.














Loughney, et al.            Standards Track                    [Page 45]

RFC 3868                          SUA                       October 2004


3.4.4.  Signalling Congestion (SCON)

  The SCON message can be sent from the SG or relay node to all
  concerned ASPs to indicate that the congestion level in the SS7
  network to a specified destination has changed.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0006          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0012          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                        Affected Point Code                    /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x8003          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                              SSN                              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0118          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                       Congestion Level                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0112          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                              SMI                              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0004          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                          Info String                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Optional
    Affected Point Code           Mandatory *1
    SSN                           Optional *1
    Congestion Level              Mandatory
    SMI                           Optional
    Info String                   Optional

  Note 1:    When the SSN is included, the SCON message corresponds to
             the SCCP N-STATE primitive.  When the SSN is not
             included, the SCON message corresponds to the SCCP



Loughney, et al.            Standards Track                    [Page 46]

RFC 3868                          SUA                       October 2004


             N-PCSTATE primitive reporting signalling point or network
             congestion status.

3.4.5.  Destination User Part Unavailable (DUPU)

  The DUPU message is used by an SG to inform an ASP that a remote peer
  at an SS7 node is unavailable.

  The format for DUPU message parameters is as follows:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0006          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0012          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                        Affected Point Code                    /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010C          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                           User/Cause                          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0004          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  \                                                               \
  /                          INFO String                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Optional
    Affected Point Code           Mandatory *1
    User/Cause                    Mandatory
    Info String                   Optional

  Note 1:    The DUPU corresponds to the SCCP N-PCSTATE primitive.

3.4.6.  Destination Restricted (DRST)

  The DRST message is optionally sent from the SG to all concerned ASPs
  to indicate that the SG has determined that one or more destinations
  are now restricted from the point of view of the SG, or in response
  to a DAUD message if appropriate.  The SUA layer at the ASP is



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  expected to send traffic to the affected destination via an alternate
  SG of equal priority, but only if such an alternate route exists and
  is available.  If the ASP currently considers the affected
  destination unavailable, the peer should be informed that traffic to
  the affected destination could be resumed.  In this case, the SUA
  layer should route the traffic through the SG initiating the DRST
  message.

  This message is optional for the SG to send and it is optional for
  the ASP to act on any information received in the message.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0006          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0012          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                        Affected Point Code                    /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x8003          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                              SSN                              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0112          |            Length = 8         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    Reserved                  |       SMI      |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0004          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                          Info String                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context               Optional
    Affected Point Code           Mandatory *1
    SSN                           Optional *1
    SMI                           Optional *1
    Info String                   Optional

  Note 1:    The Affected Point Code refers to the node to which
             become restricted or which has requested coordinated
             service outage.  When SSN is included in the message



Loughney, et al.            Standards Track                    [Page 48]

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             parameter, the DRST message corresponds to the SCCP
             N-COORD primitive.  If the SMI parameter is also included
             in the message, the DRST message corresponds to the
             N-COORD Request and N-COORD Indication primitives,
             otherwise, the DRST message correspondence to the N-COORD
             Response and N-COORD Confirm primitives.  The Affected
             Point Code can only contain one point code when SSN is
             present.  When SSN is not present, DRST corresponds to
             N-PCSTATE primitive.

3.5.  Application Server Process State Maintenance Messages

3.5.1.  ASP Up (UP)

  The ASP UP (UP) message is used to indicate to a remote SUA peer that
  the Adaptation layer is up and running.

   0                     1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |            Tag = 0x0011       |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        ASP Identifier                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |            Tag = 0x0004       |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                          Info String                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    ASP Identifier                Optional *1
    Info String                   Optional

  Note 1:    ASP Identifier MUST be used where the IPSP/SGP cannot
             identify the ASP by provisioned address/port number
             information (e.g., where an ASP is resident on a Host
             using dynamic address/port number assignment).













Loughney, et al.            Standards Track                    [Page 49]

RFC 3868                          SUA                       October 2004


3.5.2.  ASP Up Ack (UP ACK)

  The ASP UP Ack message is used to acknowledge an ASP-Up message
  received from a remote SUA peer.

   0                     1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |            Tag = 0x0004       |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                          Info String                          /

  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Info String              Optional

3.5.3.  ASP Down (DOWN)

  The ASP Down (DOWN) message is used to indicate to a remote SUA peer
  that the adaptation layer is not running.

   0                     1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Tag = 0x0004        |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                          Info String                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Info String         Optional

















Loughney, et al.            Standards Track                    [Page 50]

RFC 3868                          SUA                       October 2004


3.5.4.  ASP Down Ack (DOWN ACK)

  The ASP DOWN Ack message is used to acknowledge an ASP-Down message
  received from a remote SUA peer.

   0                     1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Tag = 0x0004        |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                          Info String                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Info String         Optional

  Note:    ASP DOWN ACK will always be sent to acknowledge an ASP DOWN.

3.5.5.  Heartbeat (BEAT)

  The Heartbeat message is optionally used to ensure that the SUA peers
  are still available to each other.

  The format for the BEAT message is as follows:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Tag = 0x0009        |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Heartbeat Data                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Heartbeat Data      Optional














Loughney, et al.            Standards Track                    [Page 51]

RFC 3868                          SUA                       October 2004


3.5.6.  Heartbeat Ack (BEAT ACK)

  The Heartbeat ACK message is sent in response to a BEAT message.  A
  peer MUST send a BEAT ACK in response to a BEAT message.  It includes
  all the parameters of the received Heartbeat message, without any
  change.

  The format for the BEAT ACK message is as follows:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Tag = 0x0009        |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Heartbeat Data                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Heartbeat Data      Optional































Loughney, et al.            Standards Track                    [Page 52]

RFC 3868                          SUA                       October 2004


3.6.  ASP Traffic Maintenance Messages

3.6.1.  ASP Active (ACTIVE)

  The ASPAC message is sent by an ASP to indicate to a remote SUA peer
  that it is Active and ready to process signalling traffic for a
  particular Application Server.

  The format for the ACTIVE message is as follows:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Tag = 0x000B        |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                       Traffic Mode Type                       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Tag = 0x0006        |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0110         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                           TID Label                           |
  +-------------------------------+-------------------------------+
  |          Tag = 0x010F         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                           DRN Label                           |
  +-------------------------------+-------------------------------+
  |           Tag = 0x0004        |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                          Info String                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Traffic Mode Type   Optional
    Routing Context     Optional
    TID Label           Optional
    DRN Label           Optional
    Info String         Optional









Loughney, et al.            Standards Track                    [Page 53]

RFC 3868                          SUA                       October 2004


3.6.2.  ASP Active Ack (ACTIVE ACK)

  The ASPAC Ack message is used to acknowledge an ASP-Active message
  received from a remote SUA peer.

  The format for the ACTIVE Ack message is as follows:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Tag = 0x000B        |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                       Traffic Mode Type                       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Tag = 0x0006        |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0004         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                          Info String                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Traffic Mode Type   Optional
    Routing Context     Mandatory
    Info String         Optional






















Loughney, et al.            Standards Track                    [Page 54]

RFC 3868                          SUA                       October 2004


3.6.3.  ASP Inactive (INACTIVE)

  The INACTIVE message is sent by an ASP to indicate to a remote SUA
  peer that it is no longer processing signalling traffic within a
  particular Application Server.

  The format for the ASPIA message parameters is as follows:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Tag = 0x0006        |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Tag = 0x0004        |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                          INFO String                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Parameters
    Routing Context     Optional
    INFO String         Optional

3.6.4.  ASP Inactive Ack (INACTIVE ACK)

  The INACTIVE Ack message is used to acknowledge an ASP-Inactive
  message received from a remote SUA peer.

  The format for the INACTIVE Ack message is as follows:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0006         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0004         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                          INFO String                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





Loughney, et al.            Standards Track                    [Page 55]

RFC 3868                          SUA                       October 2004


  Parameters
    Routing Context     Optional
    INFO String         Optional

3.7.  SUA Management Messages

  These messages are used for managing SUA and the representations of
  the SCCP subsystems in the SUA layer.

3.7.1.  Error (ERR)

  The ERR message is sent between two SUA peers to indicate an error
  situation.  The Diagnostic Information parameter is optional,
  possibly used for error logging and/or debugging.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x000C         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          Error Code                           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0006          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0012          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |      Mask     |                 Affected PC 1                 |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                              ...                              /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |      Mask     |                 Affected PC n                 |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010D          |         Length = 8            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                     Network Appearance                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0007         |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                        Diagnostic Info                        /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






Loughney, et al.            Standards Track                    [Page 56]

RFC 3868                          SUA                       October 2004


  Parameters
    Error Code                    Mandatory
    Routing Context               Mandatory *1
    Network Appearance            Mandatory *1
    Affected Point Code           Mandatory *1
    Diagnostic Information        Optional

  Note 1:    Only mandatory for specific error codes.

3.7.2.  Notify (NTFY)

  The Notify message used to provide an autonomous indication of SUA
  events to an SUA peer.

   0                     1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x000D         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                           Status                              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |            Tag = 0x0011       |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        ASP Identifier                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
  |          Tag = 0x0006         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0004         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                          Info String                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The NTFY message contains the following parameters:

  Parameters
    Status                        Mandatory
    ASP Identifier                Optional *1
    Routing Context               Optional
    Info String                   Optional

  Note 1:    ASP Identifier MUST be used where the IPSP/SGP cannot
             identify the ASP by provisioned address/port number
             information (e.g., where an ASP is resident on a Host
             using dynamic address/port number assignment).



Loughney, et al.            Standards Track                    [Page 57]

RFC 3868                          SUA                       October 2004


3.8.  Routing Key Management (RKM) Messages

3.8.1.  Registration Request (REG REQ)

  The REG REQ message is sent by an ASP to indicate to a remote SUA
  peer that it wishes to register one or more given Routing Keys with
  the remote peer.  Typically, an ASP would send this message to an
  SGP, and expects to receive a REG RSP message in return with an
  associated Routing Context value.

  The format for the REG REQ message is as follows:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x010E         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                         Routing Key 1                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                              ...                              /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x010E         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                         Routing Key n                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |            Tag = 0x0109       |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        ASP Capabilities                       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The REG REQ message contains the following parameters:

  Parameters
    Routing Key                   Mandatory *1
    ASP Capabilities              Optional

  Note 1:   One or more Routing Key parameters MAY be included in a
            single REG REQ message.










Loughney, et al.            Standards Track                    [Page 58]

RFC 3868                          SUA                       October 2004


3.8.2.  Registration Response (REG RSP)

  The REG RSP message is sent by an SG to an ASP indicate the result of
  a previous REG REQ from an ASP.  It contains indications of
  success/failure for registration requests and returns a unique
  Routing Context value for successful registration requests, to be
  used in subsequent SUA Traffic Management protocol messages.

  The format for the REG RSP message is as follows:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0014         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    Registration Result 1                      |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                              ...                              /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0014         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    Registration Result n                      |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The REG RSP message contains the following parameters:

  Parameters
    Registration Result           Mandatory *1

  Note 1:   One or more Registration Result parameters MAY be included
            in a single REG RSP message.  The number of results in a
            single REG RSP message can be anywhere from one to the
            total number of Routing Key parameters found in the
            corresponding REG REQ message.

3.8.3.  Deregistration Request (DEREG REQ)

  The DEREG REQ message is sent by an ASP to indicate to a remote SUA
  peer that it wishes to deregister a given Routing Key.  Typically, an
  ASP would send this message to an SGP, and expects to receive a DEREG
  RSP message in return with the associated Routing Context value.









Loughney, et al.            Standards Track                    [Page 59]

RFC 3868                          SUA                       October 2004


  The format for the DEREG REQ message is as follows:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0006            |           Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The DEREG REQ message contains the following parameters:

  Parameters
    Routing Context               Mandatory

3.8.4.  Deregistration Response (DEREG RSP)

  The DEREG RSP message is used as a response to the DEREG REQ message
  from a remote SUA peer.

  The format for the DEREG RSP message is as follows:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0015         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                   Deregistration Result 1                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                              ...                              /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0015         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                   Deregistration Result n                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The DEREG RSP message contains the following parameters:

  Parameters
    Deregistration Result         Mandatory *1

  Note 1:    One or more Deregistration Result parameters MAY be
             included in one DEREG RSP message.  The number of results
             in a single DEREG RSP message can be anywhere from one to
             the total number of Routing Context parameters found in
             the corresponding DEREG REQ message.



Loughney, et al.            Standards Track                    [Page 60]

RFC 3868                          SUA                       October 2004


3.9.  Common Parameters

  These TLV parameters are common across the different adaptation
  layers.

  Parameter Name                     Parameter ID
  ==============                     ============
  Reserved                             0x0000
  Not used in SUA                      0x0001
  Not used in SUA                      0x0002
  Not used in SUA                      0x0003
  Info String                          0x0004
  Not used in SUA                      0x0005
  Routing Context                      0x0006
  Diagnostic Info                      0x0007
  Not used in SUA                      0x0008
  Heartbeat Data                       0x0009
  Not Used in SUA                      0x000A
  Traffic Mode Type                    0x000B
  Error Code                           0x000C
  Status                               0x000D
  Not used in SUA                      0x000E
  Not used in SUA                      0x000F
  Not used in SUA                      0x0010
  ASP Identifier                       0x0011
  Affected Point Code                  0x0012
  Correlation ID                       0x0013
  Registration Result                  0x0014
  Deregistration Result                0x0015
  Registration Status                  0x0016
  Deregistration Status                0x0017
  Local Routing Key Identifier         0x0018

3.9.1.  Not Used

  Use of Parameter ID 0x0001 in SUA messages is not supported.

3.9.2.  Not Used

  Use of Parameter ID 0x0002 in SUA messages is not supported.

3.9.3.  Not Used

  Use of Parameter ID 0x0003 in SUA messages is not supported.







Loughney, et al.            Standards Track                    [Page 61]

RFC 3868                          SUA                       October 2004


3.9.4.  Info String

  The optional INFO String parameter can carry any meaningful UTF-8
  [3629] character string along with the message.  Length of the INFO
  String parameter is from 0 to 255 octets.  No procedures are
  presently identified for its use but service providers may use the
  INFO String for debugging purposes.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0004         |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                          Info String                          /

  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.9.5.  Not Used in SUA

  Use of Parameter ID 0x0005 in SUA messages is not supported.

3.9.6.  Routing Context

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0006         |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Routing Context                         /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The Routing Context parameter contains (a list of) 4-byte unsigned
  integers indexing the Application Server traffic that the sending ASP
  is configured/registered to receive.  There is a one-to-one
  relationship between an index entry and a Routing Key or AS Name.

  An Application Server Process may be configured to process traffic
  for more than one logical Application Server.  From the perspective
  of an ASP, a Routing Context defines a range of signalling traffic
  that the ASP is currently configured to receive from the SG.

  Additionally, the Routing Context parameter identifies the SS7
  network context for the message, for the purposes of logically
  separating the signalling traffic between the SGP and the Application
  Server Process over a common SCTP Association, when needed.  An
  example is where an SGP is logically partitioned to appear as an



Loughney, et al.            Standards Track                    [Page 62]

RFC 3868                          SUA                       October 2004


  element in several different national SS7 networks.  It implicitly
  defines the SS7 Point Code format used, the SS7 Network Indicator
  value and SCCP protocol type/variant/version used within a separate
  SS7 network.  It also defines the network context for the PC and SSN
  values.  Where an SGP operates in the context of a single SS7
  network, or individual SCTP associations are dedicated to each SS7
  network context, this functionality is not needed.

  If the Routing Context parameter is present, it SHOULD be the first
  parameter in the message as it defines the format and/or
  interpretation of the parameters containing a PC or SSN value.

3.9.7.  Diagnostic Information

  The Diagnostic Information can be used to convey any information
  relevant to an error condition, to assist in the identification of
  the error condition.  In the case of an Adaptation Layer Identifier
  or Traffic Handling Mode, the Diagnostic Information includes the
  received parameter.  In the other cases, the Diagnostic information
  may be the first 40 bytes of the offending message.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0007          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                     Diagnostic Information                    /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.9.8.  Not Used

  Parameter ID 0x0008 is not used in SUA.

3.9.9.  Heartbeat Data

  The sending node defines the Heartbeat Data field contents.  It may
  include a Heartbeat Sequence Number and/or Timestamp, or other
  implementation specific details.

  The receiver of a Heartbeat message does not process this field as it
  is only of significance to the sender.  The receiver echoes the
  content of the Heartbeat Data in a BEAT-Ack message.








Loughney, et al.            Standards Track                    [Page 63]

RFC 3868                          SUA                       October 2004


   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0009          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Heartbeat Data                          /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The data field can be used to store information in the heartbeat
  message useful to the sending node (e.g., the data field can contain
  a time stamp, a sequence number, etc.).

3.9.10.  Not Used

  Parameter ID 0x000A is not used in SUA.

3.9.11.  Traffic Mode Type

  The Traffic Mode Type parameter identifies the traffic mode of
  operation of the ASP within an AS.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x000B         |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                      Traffic Mode Type                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The valid values for Type are shown in the following table.

     1         Override
     2         Loadshare
     3         Broadcast

  Within a Routing Context, Override, Loadshare Types and Broadcast
  cannot be mixed.  The Override value indicates that the ASP is
  operating in Override mode, and the ASP wishes to take over all
  traffic for an Application Server (i.e., primary/backup operation),
  overriding any currently active ASP in the AS.  In Loadshare mode,
  the ASP wishes to share in the traffic distribution with any other
  currently active ASPs.  In Broadcast mode, the ASP wishes to receive
  the same traffic as any other currently active ASPs.  When there are
  insufficient ASPs, the sender may immediately move the ASP to Active.






Loughney, et al.            Standards Track                    [Page 64]

RFC 3868                          SUA                       October 2004


3.9.12.  Error Code

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |        Tag =0x000C            |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          Error Code                           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The Error Code parameter indicates the reason for the Error Message.
  The Error parameter value can be one of the following values:

     0x01      Invalid Version
     0x02      Not Used in SUA
     0x03      Unsupported Message Class
     0x04      Unsupported Message Type
     0x05      Unsupported Traffic Handling Mode
     0x06      Unexpected Message
     0x07      Protocol Error
     0x08      Not used in SUA
     0x09      Invalid Stream Identifier
     0x0a      Not used in SUA
     0x0b      Not used in SUA
     0x0c      Not used in SUA
     0x0d      Refused - Management Blocking
     0x0e      ASP Identifier Required
     0x0f      Invalid ASP Identifier
     0x10      Not Used in SUA
     0x11      Invalid Parameter Value
     0x12      Parameter Field Error
     0x13      Unexpected Parameter
     0x14      Destination Status Unknown
     0x15      Invalid Network Appearance
     0x16      Missing Parameter
     0x17      Not Used in SUA
     0x18      Not Used in SUA
     0x19      Invalid Routing Context
     0x1a      No Configured AS for ASP
     0x1b      Subsystem Status Unknown
     0x1c      Invalid loadsharing label

  The "Invalid Version" error is sent if a message was received with an
  invalid or unsupported version.  The Error message contains the
  supported version in the Common header.  The Error message could
  optionally provide the unsupported version in the Diagnostic
  information area.




Loughney, et al.            Standards Track                    [Page 65]

RFC 3868                          SUA                       October 2004


  The "Unsupported Message Class" error is sent if a message with an
  unexpected or unsupported Message Class is received.

  The "Unsupported Message Type" error is sent if a message with an
  unexpected or unsupported Message Type is received.

  The "Unsupported Traffic Handling Mode" error is sent by a SGP if an
  ASP sends an ASP Active message with an unsupported Traffic Mode Type
  or a Traffic Mode Type that is inconsistent with the presently
  configured mode for the Application Server.  An example would be a
  case in which the SGP did not support loadsharing.

  The "Unexpected Message" error MAY be sent if a defined and
  recognized message is received that is not expected in the current
  state (in some cases the ASP may optionally silently discard the
  message and not send an Error message).  For example, silent discard
  is used by an ASP if it received a DATA message from an SGP while it
  was in the ASP-INACTIVE state.  If the Unexpected message contained
  Routing Context(s), the Routing Context(s) SHOULD be included in the
  Error message.

  The "Protocol Error" error is sent for any protocol anomaly (i.e.,
  reception of a parameter that is syntactically correct but unexpected
  in the current situation.

  The "Invalid Stream Identifier" error is sent if a message is
  received on an unexpected SCTP stream.

  The "Refused - Management Blocking" error is sent when an ASP Up or
  ASP Active message is received and the request is refused for
  management reasons (e.g., management lockout").  If this error is in
  response to an ASP Active message, the Routing Context(s) in the ASP
  Active message SHOULD be included in the Error message.

  The "ASP Identifier Required" is sent by a SGP in response to an ASP
  Up message that does not contain an ASP Identifier parameter when the
  SGP requires one.  The ASP SHOULD resend the ASP Up message with an
  ASP Identifier.

  The "Invalid ASP Identifier" is send by a SGP in response to an ASP
  Up message with an invalid ASP Identifier.

  The "Invalid Parameter Value" error is sent if a message is received
  with an invalid parameter value (e.g., a DUPU message was received
  with a Mask value other than "0".

  The "Parameter Field Error" would be sent if a message is received
  with a parameter having a wrong length field.



Loughney, et al.            Standards Track                    [Page 66]

RFC 3868                          SUA                       October 2004


  The "Unexpected Parameter" error would be sent if a message contains
  an invalid parameter.

  The "Invalid Network Appearance" error is sent by a SGP if an ASP
  sends a message with an invalid (not configured) Network Appearance
  value.  For this error, the invalid (not configured) Network
  Appearance MUST be included in the Network Appearance parameter.

  The "Missing Parameter" error would be sent if a mandatory parameter
  were not included in a message.

  The "Invalid Routing Context" error would be sent by a SG if an ASP
  sends a message with an invalid (not configured) Routing Context
  value.  For this error, the invalid (not configured) Routing
  Context(s) MUST be included in the Routing Context parameter.

  The "No Configured AS for ASP" error is sent if a message is received
  from a peer without a Routing Context parameter and it is not known
  by configuration data, which Application Servers are referenced.

  The "Destination Status Unknown" Error MAY be sent if a DAUD is
  received at an SG inquiring of the availability or congestion status
  of a destination, and the SG does not wish to provide the status
  (e.g., the sender is not authorized to know the status).  For this
  error, the invalid or unauthorized Point Code(s) MUST be included
  along with the Network Appearance and Routing Context associated with
  the Point Code(s).

  The "Subsystem Status Unknown" Error MAY be sent if a DAUD is
  received at an SG inquiring of the availability or congestion status
  of a subsystem, and the SG does not wish to provide the status (e.g.,
  the sender is not authorized to know the status).  For this error,
  the invalid or unauthorized Point Code and Subsystem Number MUST be
  included along with the Network Appearance and Routing Context
  associated with the Point Code and Subsystem Number.

3.9.13.  Status

  The Status parameter identifies the type of the status that is being
  notified and the Status ID.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x000D         |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Status Type           |            Status ID          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



Loughney, et al.            Standards Track                    [Page 67]

RFC 3868                          SUA                       October 2004


  The valid values for Status Type (16 bit unsigned integer) are:

     1     Application Server state change (AS_State_Change)
     2     Other

  The Status ID parameter contains more detailed information for the
  notification, based on the value of the Status Type.

  If the Status Type is AS_STATE_CHANGE, then the Status ID (16 bit
  unsigned integer) values are:

     1    reserved
     2    Application Server Inactive (AS-Inactive)
     3    Application Server Active (AS-Active)
     4    Application Server Pending (AS-Pending)

  These notifications are sent from an SGP to an ASP upon a change in
  status of a particular Application Server.  The value reflects the
  new state of the Application Server.

  If the Status Type is "Other", then the following Status Information
  values are defined:

     1    Insufficient ASP resources active in AS
     2    Alternate ASP Active
     3    ASP failure

  These notifications are not based on the SGP reporting the state
  change of an ASP or AS.  In the Insufficient ASP Resources case, the
  SGP is indicating to an "Inactive" ASP(s) in the AS that another ASP
  is required to handle the load of the AS (Loadsharing mode or
  Broadcast mode).  For the Alternate ASP Active case, an ASP is
  informed when an alternate ASP transitions to the ASP-Active state in
  Override mode.

3.9.14.  Not Used in SUA

  Parameter ID 0x000E is not used in SUA.













Loughney, et al.            Standards Track                    [Page 68]

RFC 3868                          SUA                       October 2004


3.9.15.  Not Used in SUA

  Parameter ID 0x000F is not used in SUA.

3.9.16.  Not Used in SUA

  Parameter ID 0x0010 is not used in SUA.

3.9.17.  ASP Identifier

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0011          |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        ASP Identifier                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  ASP Identifier field: 32-bits (unsigned integer)

  The ASP Identifier field contains a unique value that is locally
  significant among the ASPs that support an AS.  The SGP should save
  the ASP Identifier to be used, if necessary, with the Notify message
  (see Section 3.7.2).

3.9.18.  Affected Point Code

  The Affected Point Code Destinations parameter contains a list of
  Affected Point Code fields, each a three-octet parameter to allow for
  14-, 16- and 24-bit binary formatted SS7 Point Codes.  Affected Point
  Codes that are less than 24-bits are padded on the left to the 24-bit
  boundary.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0012         |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |    Mask       |                 Affected PC 1                 |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                             . . .                             /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The encoding is shown below for ANSI and ITU Point Code examples.






Loughney, et al.            Standards Track                    [Page 69]

RFC 3868                          SUA                       October 2004


  ANSI 24-bit Point Code:

   0                   1                   2                   3-->
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |     Mask      |    Network    |    Cluster    |     Member    |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  |MSB-----------------------------------------LSB|

  ITU 14-bit Point Code:

   0                   1                   2                   3-->
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |     Mask      |0 0 0 0 0 0 0 0 0 0|Zone |     Region    | SP  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                       |MSB--------------------LSB|

  It is OPTIONAL for an implementation to generate an Affected Point
  Code parameter with more than on Affected PC but the implementation
  MUST accept and process an Affected Point Code parameter with more
  than one Affected PC.

  Mask: 8-bits

  The Mask parameter can be used to identify a contiguous range of
  Affected Destination Point Codes, independent of the point code
  format.  Identifying a contiguous range of Affected PCs may be useful
  when reception of an MTP3 management message or a linkset event
  simultaneously affects the availability status of a series of
  destinations at an SG.

  The Mask parameter is an integer representing a bit mask that can be
  applied to the related Affected PC field.  The bit mask identifies
  how many bits of the Affected PC field are significant and which are
  effectively "wild-carded".  For example, a mask of "8" indicates that
  the last eight bits of the PC is "wild-carded".  For an ANSI 24-bit
  Affected PC, this is equivalent to signalling that all PCs in an ANSI
  Cluster are unavailable.  A mask of "3" indicates that the last three
  bits of the PC is "wild-carded".  For a 14-bit ITU Affected PC, this
  is equivalent to signalling that an ITU Region is unavailable.










Loughney, et al.            Standards Track                    [Page 70]

RFC 3868                          SUA                       October 2004


3.9.19.  Correlation ID

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0013         |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        Correlation ID                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The Correlation ID is a 32-bit identifier that is attached to CLDT
  messages to indicate to a newly entering ASP in a Broadcast AS where
  in the traffic flow of CLDT messages the ASP is joining.  It is
  attached to the first CLDT message sent to an ASP by an SG after
  sending an ASP Active Ack or otherwise starting traffic to an ASP.
  The Correlation ID is only significant within a Routing Context.

  Implementation note: Correlation ID parameter can be used for
  features like Synchronisation of ASPs/SGPs in a Broadcast Mode AS/SG;
  avoid message duplication and mis-sequencing in case of failover of
  association from one ASP/SGP to other ASP/SGP etc.

3.9.20.  Registration Result

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0018         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                     Routing Key Identifier                    |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0016         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                       Registration Status                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0006         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                         Routing Context                       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Routing Key Identifier contains the same TLV formatted parameter
  value as found in the matching Routing Key parameter in the REG REQ
  message.

  Routing Context contains the same TLV formatted Routing Context
  parameter for the associated Routing Key if the registration was
  successful.  It is set to "0" if the registration was not successful.




Loughney, et al.            Standards Track                    [Page 71]

RFC 3868                          SUA                       October 2004


3.9.21.  Deregistration Result

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0006         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                         Routing Context                       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0017         |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                      Deregistration Status                    |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Routing Context: 32-bit integer

     Routing Context contains the Routing Context value of the matching
     Routing key to deregister, as found in the DEREG REQ message.

  Deregistration Status: 32-bit integer

     Deregistration Status parameter indicates the success or the
     reason for failure of the deregistration.

3.9.22.  Registration Status

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Tag = 0x0016      |          Length = 8             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                      Registration Status                      |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Registration Status: 32-bits (unsigned integer)

     The Registration Status field indicates the success or the reason
     for failure of a registration request.

  Its values may be:
            0           Successfully Registered
            1           Error - Unknown
            2           Error - Invalid Destination Address
            3           Error - Invalid Network Appearance
            4           Error - Invalid Routing Key
            5           Error - Permission Denied
            6           Error - Cannot Support Unique Routing
            7           Error - Routing Key not Currently Provisioned



Loughney, et al.            Standards Track                    [Page 72]

RFC 3868                          SUA                       October 2004


            8           Error - Insufficient Resources
            9           Error - Unsupported RK parameter Field
           10           Error - Unsupported/Invalid Traffic Mode Type
           11           Error - Routing Key Change Refused

3.9.23.  Deregistration Status

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Tag = 0x0017      |          Length = 8             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    Deregistration Status                      |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Deregistration Status: 32-bit integer

  The Deregistration Result Status field indicates the success or the
  reason for failure of the deregistration.

  Its values may be:

  0           Successfully Deregistered
  1           Error - Unknown
  2           Error - Invalid Routing Context
  3           Error - Permission Denied
  4           Error - Not Registered
  5           Error - ASP Currently Active for Routing Context

3.9.24.  Local Routing Key Identifier

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Tag = 0x0018        |        Length = 8             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                  Local Routing Key Identifier                 |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The Local Routing Key Identifier field is a 32-bits unsigned integer.
  The Identifier value is assigned by the ASP and is used to correlate
  the response in a REG RSP message with the original registration
  request.  The Identifier value must remain unique until the REG RSP
  message is received.







Loughney, et al.            Standards Track                    [Page 73]

RFC 3868                          SUA                       October 2004


3.10.  SUA-Specific parameters

  These TLV parameters are specific to the SUA protocol.

  Parameter Name                     Parameter ID
  ==============                     ============
  SS7 Hop Counter                      0x0101
  Source Address                       0x0102
  Destination Address                  0x0103
  Source Reference Number              0x0104
  Destination Reference Number         0x0105
  SCCP Cause                           0x0106
  Sequence Number                      0x0107
  Receive Sequence Number              0x0108
  ASP Capabilities                     0x0109
  Credit                               0x010A
  Data                                 0x010B
  User/Cause                           0x010C
  Network Appearance                   0x010D
  Routing Key                          0x010E
  DRN Label                            0x010F
  TID Label                            0x0110
  Address Range                        0x0111
  SMI                                  0x0112
  Importance                           0x0113
  Message Priority                     0x0114
  Protocol Class                       0x0115
  Sequence Control                     0x0116
  Segmentation                         0x0117
  Congestion Level                     0x0118

  Destination/Source Address Sub-Parameters
  ===========================================
  Global Title                         0x8001
  Point Code                           0x8002
  Subsystem Number                     0x8003
  IPv4 Address                         0x8004
  Hostname                             0x8005
  IPv6 Addresses                       0x8006












Loughney, et al.            Standards Track                    [Page 74]

RFC 3868                          SUA                       October 2004


3.10.1.  SS7 Hop counter

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0101          |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |              Reserved                         | SS7 Hop Count |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  SS7 Hop Counter (3.18/Q.713)

  The value of the SS7 Hop Counter is decremented with each global
  title translation and is in the range 15 to 1.

3.10.2.  Source Address

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0102         |      Parameter Length         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |      Routing Indicator        |       Address Indicator       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Address parameter(s)                    /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The following combinations of address parameters are valid:

  -  Global Title (e.g., E.164 number) + optional PC and/or SSN, SSN
     may be zero, when routing is done on Global Title

  -  SSN (non-zero) + optional PC and/or Global Title, when routing is
     done on PC + SSN.  The PC is mandatory in the source address when
     sending from SGP to ASP, and in the destination address when
     sending from ASP to SGP to reach the SS7 SEP.

  -  Hostname + optional SSN, when routing is done by Hostname

  -  SSN (non-zero) and optional IP address (IPv4 or IPv6) when routing
     is done on IP address + SSN









Loughney, et al.            Standards Track                    [Page 75]

RFC 3868                          SUA                       October 2004


3.10.2.1.  Routing Indicator

  The following values are valid for the routing indicator:

     Reserved                      0
     Route on Global Title         1
     Route on SSN + PC             2
     Route on Hostname             3
     Route on SSN + IP Address     4

  The routing indicator determines which address parameters need to be
  present in the address parameters field.

3.10.2.2.  Address Indicator

  This parameter is needed for interworking with SS7 networks.  The
  address indicator specifies what address parameters are actually
  received in the SCCP address from the SS7 network, or are to be
  populated in the SCCP address when the message is sent into the SS7
  network.  The value of the routing indicator needs to be taken into
  account.  It is used in the ASP to SG direction.  For example, the PC
  parameter is present in the destination address of the CLDT sent from
  ASP->SG, but bit 2 is set to "0" meaning "do not populate this in the
  SCCP called party address".  The effect is that the SG only uses the
  PC to populate the MTP routing label DPC field, but does not include
  it in the SCCP called party address.

  In the SG->ASP direction, the source address PC parameter is present
  (PC of SS7 SEP).  However, this may have been populated from the OPC
  in the received MTP routing label, not from the PC field in the SCCP
  calling party address.  In this case, bit 2 = "0" denotes that.  The
  AI gives further instructions to the SG how and when to populate the
  SCCP addresses; in the SG->ASP direction, the AI gives information to
  the ASP as to what was actually present in the received SCCP
  addresses.

  The address indicator is coded as follows:

  Bit 1 is used to indicate inclusion of the SSN

  0         Do not include SSN when optional
   1         Include SSN

  Bit 2 is used to indicate inclusion of the PC

  0         Do not include PC, regardless of the routing indicator
            value
   1        Include PC



Loughney, et al.            Standards Track                    [Page 76]

RFC 3868                          SUA                       October 2004


  Bit 3 is used to indicate inclusion of the Global Title

  0         Do not include GT when optional (routing indicator /= 1)
   1        Include GT

  The remaining bits are spare and SHOULD be coded zero, and MUST be
  ignored by the receiver.

3.10.2.3.  Global Title

  0                 1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x8001          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                Reserved                       |      GTI      |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   No. Digits  | Trans. type   |    Num. Plan  | Nature of Add |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                         Global Title Digits                   /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Number of Digits:

  This is the number of digits contained in the Global Title.

  GTI (Global Title Indicator, defined in chapter 3.4.2.3 of Q.713).

  0000     Invalid
  0001     Nature of Address is taken over. It is implicitly assumed
            that the Translation Type = Unknown and Numbering Plan =
            E.164 (value 1).
  0010     This is most commonly used in North American networks.
            The Translation Type implicitly determines Nature of
            Address and Numbering Plan.  This data can be configured
            in the SG.  The number of digits is always even and
            determined by the SCCP address length.
  0011     Numbering Plan and Translation Type are taken over.  It is
            implicitly assumed that the Nature of Address = Unknown.
  0100     This format is used in international networks and most
            commonly in networks outside North America.  All
            information to populate the source address is present in
            the SCCP Address.







Loughney, et al.            Standards Track                    [Page 77]

RFC 3868                          SUA                       October 2004


  Translation type:

  0              Unknown
  1 - 63         International services
  64 - 127       Spare
  128 - 254      National network specific
  255            Reserved

  Numbering Plan:

  0         unknown
  1         ISDN/telephony numbering plan (Recommendations E.163 and
            E.164)
  2         generic numbering plan
  3         data numbering plan (Recommendation X.121)
  4         telex numbering plan (Recommendation F.69)
  5         maritime mobile numbering plan (Recommendations E.210,
            E.211)
  6         land mobile numbering plan (Recommendation E.212)
  7         ISDN/mobile numbering plan (Recommendation E.214)
  8 - 13    spare
  14        private network or network-specific numbering plan
  15 - 126  spare
  127       reserved.

  Nature of Address:

  0         unknown
  1         subscriber number
  2         reserved for national use
  3         national significant number
  4         international number
  5 - 255   Spare


















Loughney, et al.            Standards Track                    [Page 78]

RFC 3868                          SUA                       October 2004


  Global Title:

  Octets contain a number of address signals and possibly filler as
  shown:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |2 addr.|1 addr.|4 addr.|3 addr.|6 addr.|5 addr.|8 addr.|7 addr.|
  |  sig. | sig.  |  sig. | sig.  |  sig. | sig.  |  sig. | sig.  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |        .............          |filler |N addr.|   filler      |
  |                               |if req | sig.  |               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  All filler bits SHOULD be set to 0.

  Address signals to be coded as defined in ITU-T Q.713 Section
  3.4.2.3.1.

3.10.2.4.  Point Code

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x8002          |            Length = 8         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                            Point Code                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  See chapter 3.9.18 Affected Point Code for the layout of the Point
  Code field.

3.10.2.5.  Subsystem Number

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x8003          |            Length = 8         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Reserved                      |   SSN value   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The internationally standardized SSN values are described in chapter
  3.4.2.2 of Q.713.






Loughney, et al.            Standards Track                    [Page 79]

RFC 3868                          SUA                       October 2004


3.10.2.6.  IP Addresses

  The IP address formats can use different tags.  It should be noted
  that if the source address is in a certain IP version, the
  destination address should also be in the same IP version.

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |      Tag = 0x8004/0x8006      |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                        IPv4 or IPv6 Address                   /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Note:    The tag value 0x8004 is for an IPv4 address and 0x8006 is
           for IPv6.

3.10.2.7.  Hostname

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x8005          |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                           Host Name                           /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Host Name: variable length

  This field contains a host name in "host name syntax" per RFC 1123
  Section 2.1 [1123].  The method for resolving the host name is out of
  scope for this document.

  Note:    At least one null terminator is included in the Host Name
           string and must be included in the length.














Loughney, et al.            Standards Track                    [Page 80]

RFC 3868                          SUA                       October 2004


3.10.3.  Destination Address

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0103         |      Parameter Length         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |      Routing Indicator        |       Address Indicator       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                       Address Parameter(s)                    /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The format of this parameter is identical to the Source Address
  parameter.

3.10.4.  Source Reference Number

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0104         |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                   Source Reference Number                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The source reference number is a 4 octet long integer.  This is
  allocated by the source SUA instance.

3.10.5.  Destination Reference Number

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0105         |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Destination Reference Number                  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The destination reference number is a 4 octet long integer.  This is
  allocated by the destination SUA instance.










Loughney, et al.            Standards Track                    [Page 81]

RFC 3868                          SUA                       October 2004


3.10.6.  SCCP Cause

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0106          |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Reserved              |   Cause Type  |  Cause Value  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  This parameter bundles the SCCP parameters Release cause, Return
  cause, Reset cause, Error cause and Refusal cause.

  Cause Type can have the following values:

     Return Cause          0x1
     Refusal Cause         0x2
     Release Cause         0x3
     Reset Cause           0x4
     Error Cause           0x5

  Cause Value contains the specific cause value.  Below gives examples
  for ITU SCCP values.  ANSI references can be found in ANSI T1.112.3

  Cause value in        Correspondence with Reference
  SUA message           SCCP parameter
  ------------------    -----------------   ---------
  CLDR                  Return Cause        ITU-T Q.713 Chap 3.12
  COREF                 Refusal Cause       ITU-T Q.713 Chap 3.15
  RELRE                 Release Cause       ITU-T Q.713 Chap 3.11
  RESRE                 Reset Cause         ITU-T Q.713 Chap 3.13
  ERR                   Error Cause         ITU-T Q.713 Chap 3.14

3.10.7.  Sequence Number

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0107         |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Reserved              |  Rec Seq Num|M| Sent Seq Num  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  This parameter is used to indicate whether "more" data will follow in
  subsequent CODT messages, and/or to number each CODT message
  sequentially for the purpose of flow control.  It contains the
  received as well as the sent sequence number, P(R) and P(S) in Q.713,
  chapters 3.7 and 3.9.



Loughney, et al.            Standards Track                    [Page 82]

RFC 3868                          SUA                       October 2004


  As such it can also be used to acknowledge the receipt of data
  transfers from the peer in case of protocol class 3.

  Sent Sequence Number is one octet and is coded as follows:

     Bits 2-8 are used to indicate the Send Sequence Number P(S).
     Bit 1 (LSB) of octet 1 is spare.

  Received Sequence Number is one octet, and is coded as follows:

     Bits 2-8 are used to indicate the Received Sequence Number
     P(R).
     Bit 1 (LSB) is used for the more data indication, as follows:

     0         no more data
     1         more data

3.10.8.  Receive Sequence Number

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0108         |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    Reserved                   |  Rec Seq Num  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  This parameter is used exclusively for protocol class 3 in the data
  acknowledgement message to indicate the lower edge of the receiving
  window.  See Q.713, chapter 3.9.

  It is a 1 octet long integer coded as follows:

     Bits 8-2 are used to indicate the Received Sequence Number P(R).

     Bit 1 is spare.















Loughney, et al.            Standards Track                    [Page 83]

RFC 3868                          SUA                       October 2004


3.10.9.  ASP Capabilities

  This parameter is used so that the ASP can report its capabilities
  regarding SUA for supporting different protocol classes and
  interworking scenarios.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0109         |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Reserved              |0 0 0 0|a|b|c|d| Interworking  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Flags

    a - Protocol Class 3
    b - Protocol Class 2
    c - Protocol Class 1
    d - Protocol Class 0

  It is mandatory to support at least Protocol Class 0.

  Interworking

  Values

    0x0 indicates no interworking with SS7 Networks.
    0x1 indicates IP Signalling Endpoint (ASP), interworking with SS7
       networks.
    0x2 indicates Signalling Gateway.
    0x3 indicates relay node support.

3.10.10.  Credit

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x010A         |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Reserved                     |     Credit     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The length of the credit field is one octet.  See ITU-T Q.713 Chapter
  3.10.  The parameter is used for protocol class 3 exclusively.






Loughney, et al.            Standards Track                    [Page 84]

RFC 3868                          SUA                       October 2004


3.10.11.  Data

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x010b         |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  /                             Data                              /
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The Data parameter field contains the SS7 SCCP-User application
  message, for example an INAP/TCAP message.

3.10.12.  User/Cause

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010c          |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |             Cause             |            User               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  "User" is coded to that SCCP's SI value.  There may be several SCCP's
  at a given point code, each with different SI values, although
  normally there is only one with SI = 3.

  Cause may take the following values

  0    remote SCCP unavailable, reason unknown;
  1    remote SCCP unequipped;
  2    remote SCCP inaccessible;


















Loughney, et al.            Standards Track                    [Page 85]

RFC 3868                          SUA                       October 2004


3.10.13.  Network Appearance

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x010D          |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                      Network Appearance                       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Network Appearance field: 32-bits (unsigned integer)

     The Network Appearance field identifies the SS7 network context
     for the Routing Key.  The Network Appearance value is of local
     significance only, coordinated between the SG and ASP.  Therefore,
     in the case where the ASP is connected to more than one SG, the
     same SS7 Network context may be identified by different Network
     Appearance values depending upon to which SG the ASP is
     registering.

     In the Routing Key, the Network Appearance identifies the SS7
     Point Code and Global Title Translation Type format used, and the
     SCCP and possibly the SCCP-User protocol (type, variant and
     version) used within the specific SS7 network.

3.10.14.  Routing Key

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Tag = 0x010E          |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Tag = 0x0018          |        Length = 8             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  Local Routing Key Identifier                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \                         Key parameter(s)                      \
     /                                                               /
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Local Routing Key Identifier field: 32-bits (unsigned integer)

     Key field: variable








Loughney, et al.            Standards Track                    [Page 86]

RFC 3868                          SUA                       October 2004


  The Key field contains the following parameters:

     Parameter
        Traffic Mode Type          Optional
        Network Appearance         Optional *1
        Source Address             Optional
        Destination Address        Optional
        Address Range              Optional

  Note 1:    The Network Appearance parameter must be included in the
             Routing Key when the ASP is able to register in multiple
             SS7 Network contexts.

3.10.15.  DRN Label

   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x010F         |            Length = 8         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |     start     |      end      |         label value           |
  +---------------+---------------+-------------------------------+

  The Start parameter is the start position of label, between 0 (LSB)
  and 23 (MSB).

  The End parameter is the end position of label, between 0 (LSB) and
  23 (MSB).

  Label value is a 16-bit integer, which is unique across an AS.

3.10.16.  TID Label

   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Tag = 0x0110         |            Length = 8         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |     start     |      end      |         label value           |
  +---------------+---------------+-------------------------------+

  The Start parameter is the start position of label, between 0 (LSB)
  and 31 (MSB).

  The End parameter is the end position of label, between 0 (LSB) and
  31 (MSB).







Loughney, et al.            Standards Track                    [Page 87]

RFC 3868                          SUA                       October 2004


  Label value is a 16-bit integer, which is unique across an AS.

3.10.17.  Address Range

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0111          |             Length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  \                       Address parameter(s)                    \
  /                                                               /
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Address field:

  The Address field the following parameters:

  Parameter
    Source Address              Optional *1
    Destination Address         Optional *1

  Note 1:    The Address field must contain pairs of Source Addresses
             or pairs of Destination Addresses but MUST NOT mix Source
             Addresses with Destination Addresses in the same Address
             field.

3.10.18.  SMI

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0112          |            Length = 8         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    Reserved                   |      SMI      |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Subsystem Multiplicity Indicator (SMI) can have the following
  values:

  0x00       Reserved/Unknown
  0x01       Solitary
  0x02       Duplicated
  0x03       Triplicated
  0x04       Quadruplicated
  0xff       Unspecified






Loughney, et al.            Standards Track                    [Page 88]

RFC 3868                          SUA                       October 2004


3.10.19.  Importance

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0113          |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                Reserved                       |   Importance  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Importance (3.19/Q.713)

  Possible values of the Importance Parameter are between 0 and 7,
  where the value of 0 indicates the least important and 7 indicates
  the most important.

3.10.20.  Message Priority (or Priority)

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0114          |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |              Reserved                         |  Msg Priority |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Priority

  Priority value ranges from 0 to 3.  If the Priority value has not
  been specified by the SCCP user, it should be set to 0xFF.  The SG
  MAY take the priority into account for determining the MTP message
  priority.  In the all-IP case, this parameter MAY be used.

  The Message Priority parameter is optional in the CLDT, CLDR, CORE,
  COAK and CODT messages.  However, for networks, which support Message
  Priority (e.g., ANSI), this parameter MUST be included but it is not
  required for those which don't (e.g., International).














Loughney, et al.            Standards Track                    [Page 89]

RFC 3868                          SUA                       October 2004


3.10.21.  Protocol Class

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0115          |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |              Reserved                         |  Protocol Cl. |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Protocol class (3.6/Q.713)

  Bits 1-2 indicate the protocol class.

     Value     Description
       0       Class 0 (connectionless service)
       1       Class 1 (connectionless service)
       2       Class 2 (connection-oriented service)
       3       Class 3 (connection-oriented service)

  Bit 8 indicates the use of the return on error procedure.

      Value     Description
       0x0      No special options
       0x1      Return message on error

  Bits 3-7 are spare and SHOULD be coded zero, and MUST be
  ignored by the receiver.

3.10.22.  Sequence Control

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0116          |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        Sequence  Control         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Sequence Control (6.2.2.2.2/Q.711)

  The field is coded with the value of the sequence control parameter
  associated with a group of messages and are chosen so as to ensure
  proper loadsharing of message groups over SLS values while ensuring
  that sequence control values within message groups have the sequence
  control value coded with the same value as the initial message of the
  message group.




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RFC 3868                          SUA                       October 2004


3.10.23.  Segmentation

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0117          |            Length = 32        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  | first/remain  |             Segmentation Reference            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The first/remaining segments field is formatted as follows: bit 8
  (MSB): indicates whether this is the first segment (1) or not (0)

  bits 1-7: indicate the number of remaining segments, value between 0
  and 15

  The field would thus be coded 1000 0000 (first, no remaining
  segments) for a unsegmented CLDT.

  The segmentation reference field is a 3 byte integer, assigned by the
  ASP.

3.10.24.  Congestion Level

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Tag = 0x0118          |             Length = 8        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                       Congestion Level                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Congestion Level field: 8-bits (unsigned integer)

  The Congestion Level field contains the level at which congestion has
  occurred.

  When the Congestion Level parameter is included in a SCON message
  that corresponds to an N-PCSTATE primitive, the Congestion Level
  field indicates the MTP congestion level experienced by the local or
  affected signalling point as indicated by the Affected Point Code(s)
  also in the SCON message.  In this case, valid values for the
  Congestion Level field are as follows:

     0  No Congestion or Undefined
     1  Congestion Level 1
     2  Congestion Level 2
     3  Congestion Level 3



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RFC 3868                          SUA                       October 2004


  When the Congestion Level parameter is included in a SCON message
  that corresponds to an N-STATE primitive, the Congestion Level field
  indicates the SCCP restricted importance level experienced by the
  local or affected subsystem as indicated by the Affected Point Code
  and Subsystem Number also in the SCON message. In this case, valid
  values for the Congestion Level field range from 0 to 7, where 0
  indicates the least congested and 7 indicates the most congested
  subsystem.

4.  Procedures

  The SUA layer needs to respond to various local primitives it
  receives from other layers as well as the messages that it receives
  from the peer SUA layer.  This section describes the SUA procedures
  in response to these events.

4.1.  Procedures to Support the SUA-User Layer

4.1.1.  Receipt of Primitives from SCCP

  When an SCCP Subsystem Management (SCMG) message is received from the
  SS7 network, the SGP needs to determine whether there are concerned
  Application Servers interested in subsystem status changes.  The SUA
  management function is informed with the N-State or N-Coord primitive
  upon which it formats and transfers the applicable SNMM message to
  the list of concerned ASPs using stream ID "0".

  When MTP-3 Management indications are received (MTP-PAUSE, MTP-
  RESUME, MTP-STATUS), SCCP Subsystem Management determines whether
  there are concerned local SCCP-users.  When these local SCCP-users
  are in fact Application Servers, serviced by ASPs, SUA management is
  informed with the N-PCSTATE indication primitive upon which it
  formats and transfers the applicable SNM message (DUNA, DAVA, DRST or
  SCON) to the list of concerned ASPs using stream ID "0".

  The SUA message distribution function determines the Application
  Server (AS) based on comparing the information in the N-UNITDATA
  request primitive with a provisioned Routing Key.

  From the list of ASPs within the AS table, an ASP in the ASP-ACTIVE
  state is selected and a DATA message is constructed and issued on the
  corresponding SCTP association.  If more than one ASP is in the ASP-
  ACTIVE state (i.e., traffic is to be load-shared across more than one
  ASP), one of the ASPs in the ASP_ACTIVE state is selected from the
  list.  If the ASPs are in Broadcast Mode, all active ASPs will be
  selected and the message sent to each of the active ASPs.  The
  selection algorithm is implementation dependent but could, for
  example, be round robin or based on the SLS.  The appropriate



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RFC 3868                          SUA                       October 2004


  selection algorithm must be chosen carefully as it is dependent on
  application assumptions and understanding of the degree of state
  coordination between the ASP_ACTIVE ASPs in the AS.

  In addition, the message needs to be sent on the appropriate SCTP
  stream, again taking care to meet the message sequencing needs of the
  signalling application.  DATA messages MUST be sent on an SCTP stream
  other than stream '0' when there is more than one stream.

  When there is no Routing Key match, or only a partial match, for an
  incoming SS7 message, a default treatment MAY be specified.  Possible
  solutions are to provide a default Application Server at the SGP that
  directs all unallocated traffic to a (set of) default ASP(s), or to
  drop the message and provide a notification to Layer Management in an
  M-ERROR indication primitive.  The treatment of unallocated traffic
  is implementation dependent.

4.2.  Receipt of Primitives from the Layer Management

  On receiving primitives from the local Layer Management, the SUA
  layer will take the requested action and provide an appropriate
  response primitive to Layer Management.

  An M-SCTP_ESTABLISH request primitive from Layer Management at an ASP
  or IPSP will initiate the establishment of an SCTP association.  The
  SUA layer will attempt to establish an SCTP association with the
  remote SUA peer by sending an SCTP-ASSOCIATE primitive to the local
  SCTP layer.

  When an SCTP association has been successfully established, the SCTP
  will send an SCTP-COMMUNICATION_UP notification primitive to the
  local SUA layer.  At the ASP or IPSP that initiated the request, the
  SUA layer will send an M-SCTP_ESTABLISH confirm primitive to Layer
  Management when the association setup is complete.  At the peer SUA
  layer, an M-SCTP_ESTABLISH indication primitive is sent to Layer
  Management upon successful completion of an incoming SCTP association
  setup.

  An M-SCTP_RELEASE request primitive from Layer Management initiates
  the shutdown of an SCTP association.  The SUA layer accomplishes a
  graceful shutdown of the SCTP association by sending an SCTP-SHUTDOWN
  primitive to the SCTP layer.

  When the graceful shutdown of the SCTP association has been
  accomplished, the SCTP layer returns an SCTP-SHUTDOWN_COMPLETE
  notification primitive to the local SUA layer.  At the SUA Layer that
  initiated the request, the SUA layer will send an M-SCTP_RELEASE
  confirm primitive to Layer Management when the association shutdown



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  is complete.   At the peer SUA Layer, an M-SCTP_RELEASE indication
  primitive is sent to Layer Management upon abort or successful
  shutdown of an SCTP association.

  An M-SCTP_STATUS request primitive supports a Layer Management query
  of the local status of a particular SCTP association.  The SUA layer
  simply maps the M-SCTP_STATUS request primitive to an SCTP-STATUS
  primitive to the SCTP layer.  When the SCTP responds, the SUA layer
  maps the association status information to an M-SCTP_STATUS confirm
  primitive.  No peer protocol is invoked.

  Similar LM-to-SUA-to-SCTP and/or SCTP-to-SUA-to-LM primitive mappings
  can be described for the various other SCTP Upper Layer primitives in
  RFC 2960 [2960] such as INITIALIZE, SET PRIMARY, CHANGE HEARTBEAT,
  REQUEST HEARTBEAT, GET SRTT REPORT, SET FAILURE THRESHOLD, SET
  PROTOCOL PARAMETERS, DESTROY SCTP INSTANCE, SEND FAILURE, AND NETWORK
  STATUS CHANGE.  Alternatively, these SCTP Upper Layer primitives (and
  Status as well) can be considered for modeling purposes as a Layer
  Management interaction directly with the SCTP Layer.

  M-NOTIFY indication and M-ERROR indication primitives indicate to
  Layer Management the notification or error information contained in a
  received SUA Notify or Error message respectively.  These indications
  can also be generated based on local SUA events.

  An M-ASP_STATUS request primitive supports a Layer Management query
  of the status of a particular local or remote ASP.  The SUA layer
  responds with the status in an M-ASP_STATUS confirm primitive.  No
  SUA peer protocol is invoked.  An M-AS_STATUS request supports a
  Layer Management query of the status of a particular AS.  The SUA
  responds with an M-AS_STATUS confirm primitive.  No SUA peer protocol
  is invoked.

  M-ASP_UP request, M-ASP_DOWN request, M-ASP_ACTIVE request and M-
  ASP_INACTIVE request primitives allow Layer Management at an ASP to
  initiate state changes.  Upon successful completion, a corresponding
  confirm primitive is provided by the SUA layer to Layer Management.
  If an invocation is unsuccessful, an Error indication primitive is
  provided in the primitive.  These requests result in outgoing ASP Up,
  ASP Down, ASP Active and ASP Inactive messages to the remote SUA peer
  at an SGP or IPSP.










Loughney, et al.            Standards Track                    [Page 94]

RFC 3868                          SUA                       October 2004


4.2.1.  Receipt of SUA Peer Management Messages

  Upon successful state changes resulting from reception of ASP Up, ASP
  Down, ASP Active and ASP Inactive messages from a peer SUA, the SUA
  layer MAY invoke corresponding M-ASP_UP, M-ASP_DOWN, M-ASP_ACTIVE and
  M-ASP_INACTIVE, M-AS_ACTIVE, M-AS_INACTIVE, and M-AS_DOWN indication
  primitives to the local Layer Management.

  M-NOTIFY indication and M-ERROR indication primitives indicate to
  Layer Management the notification or error information contained in a
  received SUA Notify or Error message.  These indications can also be
  generated based on local SUA events.

  All non-Transfer and non-SSNM messages, except BEAT and BEAT Ack,
  SHOULD be sent with sequenced delivery to ensure ordering.  All non-
  Transfer messages, with the exception of ASPTM, BEAT and BEAT Ack
  messages SHOULD be sent on SCTP stream '0'.  ASPTM messages MAY be
  sent on one of the streams used to carry data traffic related to the
  Routing Context(s), to minimize possible message loss.  BEAT and BEAT
  Ack messages MAY be sent using out-of-order delivery, and MAY be sent
  on any stream.

4.3.  AS and ASP State Maintenance

  The SUA layer on the SGP maintains the state of each remote ASP, in
  each Application Server that the ASP is configured to receive
  traffic, as input to the SUA message distribution function.
  Similarly, where IPSPs use SUA in a point-to-point fashion, the SUA
  layer in an IPSP maintains the state of remote IPSPs.

  Two IPSP models are defined with regards to the number of messages
  that are needed to a IPSP state change.  They are defined as follows:

  1. IPSP Single Exchange (SE) model.  Only a single exchange of ASPTM
     or ASPSM messages is needed to change the IPSP state. This means
     that a set of request from one end and acknowledge from the other
     will be enough.

  2. IPSP Double Exchange (DE) model.  Both IPSPs have to send request
     messages and both IPSPs have to acknowledge the request messages
     from the other end.  This results in a double exchange of ASPTM
     and ASPSM message, one from each end.  This configuration supports
     dynamic routing key configuration by using RKM messages in the
     same way as ASP-SGP scenario.

  To ensure interoperability, an SUA implementation supporting IPSP
  communication MUST support IPSP SE model and MAY implement IPSP DE
  model.



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  In section 4.3.1: ASP/IPSP States, only the SGP-ASP and the IPSP SE
  scenarios are described.  For the IPSP DE model, both IPSPs MUST
  follow the SGP side of the SGP-ASP procedures.

  In section 4.3.2, only the SGP-ASP scenario is described.  All of the
  procedures referring to an AS served by ASPs are also applicable to
  ASs served by IPSPs.

  In section 4.3.3, only the Management procedures for the SGP-ASP
  scenario are described.  The corresponding Management procedures for
  IPSPs are directly inferred.

  The remaining sections contain specific IPSP Considerations
  subsections.

4.3.1.  ASP States

  The state of each remote ASP/IPSP, in each AS that it is configured
  to operate, is maintained in the peer SUA layer (i.e., in the SGP or
  peer IPSP, respectively).  The state of a particular ASP/IPSP in a
  particular AS changes due to events.  The events include:

  * Reception of messages from the peer SUA layer at the ASP/IPSP;
  * Reception of some messages from the peer SUA layer at other
    ASPs/IPSPs in the AS (e.g., ASP Active message indicating
    "Override");
  * Reception of indications from the SCTP layer; or
  * Local Management intervention.

  The ASP/IPSP state transition diagram is shown in Figure 1.  The
  possible states of an ASP/IPSP are:

  ASP-DOWN: The remote SUA peer at the ASP/IPSP is unavailable and/or
  the related SCTP association is down.  Initially all ASPs/IPSPs will
  be in this state.  An ASP/IPSP in this state SHOULD NOT be sent any
  SUA messages, with the exception of Heartbeat, ASP Down Ack and Error
  messages.

  ASP-INACTIVE: The remote SUA peer at the ASP/IPSP is available (and
  the related SCTP association is up) but application traffic is
  stopped.  In this state the ASP/IPSP SHOULD NOT be sent any DATA or
  SSNM messages for the AS for which the ASP/IPSP is inactive.

  ASP-ACTIVE: The remote SUA peer at the ASP/IPSP is available and
  application traffic is active (for a particular Routing Context or
  set of Routing Contexts).





Loughney, et al.            Standards Track                    [Page 96]

RFC 3868                          SUA                       October 2004


  Figure 1: ASP/IPSP State Transition Diagram, per AS

                                     +--------------+
                                     |              |
              +----------------------|  ASP-ACTIVE  |
              |   Other ASP/ +-------|              |
              |   IPSP in AS |       +--------------+
              |   Overrides  |           ^     |
              |              |    ASPAC/ |     | ASPIA/
              |              |[ASPAC-Ack]|     | [ASPIA-Ack]
              |              |           |     v
              |              |       +--------------+
              |              |       |              |
              |              +------>| ASP-INACTIVE |
              |                      |              |
              |                      +--------------+
              |                          ^       |
       ASPDN/ |                          |     | ASPDN /
  [ASPDN-Ack/]|                   ASPUP/ |     | [ASPDN-Ack /]
    SCTP CDI/ |              [ASPUP-Ack] |     | SCTP CDI/
    SCTP RI   |                          |     | SCTP RI
              |                          |     v
              |                      +--------------+
              |                      |              |
              +--------------------->|   ASP-DOWN   |
                                     |              |
                                     +--------------+


  The transitions in brackets are just valid for the IPSP SE model
  communication while the rest are valid for both ASPs and IPSPs.

  SCTP CDI: The SCTP CDI denotes the local SCTP layer's Communication
  Down Indication to the Upper Layer Protocol (SUA) on an SGP.  The
  local SCTP layer will send this indication when it detects the loss
  of connectivity to the ASP's peer SCTP layer.  SCTP CDI is understood
  as either a SHUTDOWN_COMPLETE notification or COMMUNICATION_LOST
  notification from the SCTP layer.

  SCTP RI: The local SCTP layer's Restart indication to the upper layer
  protocol (SUA) on an SG.  The local SCTP will send this indication
  when it detects a restart from the ASP's peer SCTP layer.

4.3.2.  AS States

  The state of the AS is maintained in the SUA layer on the SGP.  The
  state of an AS changes due to events.  These events include:




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RFC 3868                          SUA                       October 2004


     * ASP state transitions
     * Recovery timer triggers

  The possible states of an AS are:

  AS-DOWN:     The Application Server is unavailable.  This state
               implies that all related ASPs are in the ASP-DOWN state
               for this AS.  Initially the AS will be in this state.
               An Application Server is in the AS-DOWN state before it
               can be removed from a configuration.

  AS-INACTIVE: The Application Server is available but no application
               traffic is active (i.e., one or more related ASPs are in
               the ASP-INACTIVE state, but none in the ASP-ACTIVE
               state).  The recovery timer T(r) is not running or has
               expired.

  AS-ACTIVE :  The Application Server is available and application
               traffic is active.  This state implies that at least one
               ASP is in the ASP-ACTIVE state.

  AS-PENDING:  An active ASP has transitioned to ASP-INACTIVE or ASP-
               DOWN and it was the last remaining active ASP in the AS.
               A recovery timer T(r) SHOULD be started and all incoming
               signalling messages SHOULD be queued by the SGP.  If an
               ASP becomes ASP-ACTIVE before T(r) expires, the AS is
               moved to the AS-ACTIVE state and all the queued messages
               will be sent to the ASP.

  If T(r) expires before an ASP becomes ASP-ACTIVE, and the SGP has no
  alternative, the SGP may stop queueing messages and discard all
  previously queued messages.  The AS will move to the AS-INACTIVE
  state if at least one ASP is in ASP-INACTIVE state, otherwise it will
  move to AS-DOWN state.

  Figure 2 shows an example AS state machine for the case where the
  AS/ASP data is provisioned.  For other cases where the AS/ASP
  configuration data is created dynamically, there would be differences
  in the state machine, especially at creation of the AS.

  For example, where the AS/ASP configuration data is not created until
  Registration of the first ASP, the AS-INACTIVE state is entered
  directly upon the first successful REG REQ from an ASP.  Another
  example is where the AS/ASP configuration data is not created until
  the first ASP successfully enters the ASP-ACTIVE state.  In this case
  the AS-ACTIVE state is entered directly.





Loughney, et al.            Standards Track                    [Page 98]

RFC 3868                          SUA                       October 2004


                   Figure 2: AS State Transition Diagram

       +----------+   one ASP trans to ACTIVE   +-------------+
       |    AS-   |---------------------------->|     AS-     |
       | INACTIVE |                             |   ACTIVE    |
       |          |<---                         |             |
       +----------+    \                        +-------------+
          ^   |         \ Tr Expiry,                ^    |
          |   |          \ at least one             |    |
          |   |           \ ASP in ASP-INACTIVE     |    |
          |   |            \                        |    |
          |   |             \                       |    |
          |   |              \                      |    |
  one ASP |   | all ASP       \            one ASP  |    | Last ACTIVE
  trans   |   | trans to       \           trans to |    | ASP trans to
  to      |   | ASP-DOWN        -------\   ASP-     |    | ASP-INACTIVE
  ASP-    |   |                         \  ACTIVE   |    | or ASP-DOWN
  INACTIVE|   |                          \          |    | (start Tr)
          |   |                           \         |    |
          |   |                            \        |    |
          |   v                             \       |    v
       +----------+                          \  +-------------+
       |          |                           --|             |
       | AS-DOWN  |                             | AS-PENDING  |
       |          |                             |  (queueing) |
       |          |<----------------------------|             |
       +----------+    Tr Expiry and no ASP     +-------------+
                       in ASP-INACTIVE state

      Tr = Recovery Timer

4.3.2.1.  IPSP Considerations

  The AS state diagram for the AS-SG case is applicable for IPSP
  communication.

4.3.3.  SUA Management Procedures for Primitives

  Before the establishment of an SCTP association the ASP state at both
  the SGP and ASP is assumed to be in the state ASP-DOWN.

  Once the SCTP association is established (see Section 4.2.1) and
  assuming that the local SUA-User is ready, the local SUA ASP
  Maintenance (ASPM) function will initiate the relevant procedures,
  using the ASP Up/ASP Down/ASP Active/ASP Inactive messages to convey
  the ASP state to the SGP (see Section 4.3.4).





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  If the SUA layer subsequently receives an SCTP-COMMUNICATION_DOWN or
  SCTP-RESTART indication primitive from the underlying SCTP layer, it
  will inform the Layer Management by invoking the M-SCTP_STATUS
  indication primitive.  The state of the ASP will be moved to ASP-
  DOWN.

  In the case of SCTP-COMMUNICATION_DOWN, the SCTP client MAY try to
  reestablish the SCTP association.  This MAY be done by the SUA layer
  automatically, or Layer Management MAY reestablish using the M-
  SCTP_ESTABLISH request primitive.

  In the case of an SCTP-RESTART indication at an ASP, the ASP is now
  considered by its SUA peer to be in the ASP-DOWN state.  The ASP, if
  it is to recover, must begin any recovery with the ASP-Up procedure.

4.3.4.  ASPM Procedures for Peer-to-Peer Messages

4.3.4.1.  ASP Up Procedures

  After an ASP has successfully established an SCTP association to an
  SGP, the SGP waits for the ASP to send an ASP Up message, indicating
  that the ASP SUA peer is available.  The ASP is always the initiator
  of the ASP Up message.  This action MAY be initiated at the ASP by an
  M-ASP_UP request primitive from Layer Management or MAY be initiated
  automatically by an SUA management function.

  When an ASP Up message is received at an SGP and internally the
  remote ASP is in the ASP-DOWN state and not considered locked-out for
  local management reasons, the SGP marks the remote ASP in the state
  ASP-INACTIVE and informs Layer Management with an M-ASP_Up indication
  primitive.  If the SGP is aware, via current configuration data,
  which Application Servers the ASP is configured to operate in, the
  SGP updates the ASP state to ASP-INACTIVE in each AS that it is a
  member.

  Alternatively, the SGP may move the ASP into a pool of Inactive ASPs
  available for future configuration within Application Server(s),
  determined in a subsequent Registration Request or ASP Active
  procedure.  If the ASP Up message contains an ASP Identifier, the SGP
  should save the ASP Identifier for that ASP.  The SGP MUST send an
  ASP Up Ack message in response to a received ASP Up message even if
  the ASP is already marked as ASP-INACTIVE at the SGP.

  If for any local reason (e.g., management lock-out) the SGP cannot
  respond with an ASP Up Ack message, the SGP responds to an ASP Up
  message with an Error message with Reason "Refused - Management
  Blocking".




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  At the ASP, the ASP Up Ack message received is not acknowledged.
  Layer Management is informed with an M-ASP_UP confirm primitive.

  When the ASP sends an ASP Up message it starts timer T(ack).  If the
  ASP does not receive a response to an ASP Up message within T(ack),
  the ASP MAY restart T(ack) and resend ASP Up messages until it
  receives an ASP Up Ack message.  T(ack) is provisioned, with a
  default of 2 seconds.  Alternatively, retransmission of ASP Up
  messages MAY be put under control of Layer Management.  In this
  method, expiry of T(ack) results in an M-ASP_UP confirm primitive
  carrying a negative indication.

  The ASP must wait for the ASP Up Ack message before sending any other
  SUA messages (e.g., ASP Active or REG REQ).  If the SGP receives any
  other SUA messages before ASPUP message is received (other than ASPDN
  - see section 4.3.4.2), the SGP SHOULD discard them.

  If an ASP Up message is received and internally the remote ASP is in
  the ASP-ACTIVE state, an ASP Up Ack message is returned, as well as
  an Error message ("Unexpected Message), and the remote ASP state is
  changed to ASP-INACTIVE in all relevant Application Servers.

  If an ASP Up message is received and internally the remote ASP is
  already in the ASP-INACTIVE state, an ASP Up Ack message is returned
  and no further action is taken.

4.3.4.1.1.  SUA Version Control

  If an ASP Up message with an unsupported version is received, the
  receiving end responds with an Error message, indicating the version
  the receiving node supports and notifies Layer Management.

  This is useful when protocol version upgrades are being performed in
  a network.  A node upgraded to a newer version should support the
  older versions used on other nodes it is communicating with.  Because
  ASPs initiate the ASP Up procedure it is assumed that the Error
  message would normally come from the SGP.

4.3.4.1.2.  IPSP Considerations

  An IPSP may be considered in the ASP-INACTIVE state after and ASPUP
  or ASPUP Ack has been received from it.  An IPSP can be considered in
  the ASP-DOWN state after an ASPDN or ASPDN Ack has been received from
  it.  The IPSP may inform Layer Management of the change in state of
  the remote IPSP using M-ASP_UP or M-ASP_DN indication or confirmation
  primitives.





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  Alternatively, when using IPSP DE model, an interchange of ASP Up
  messages from each end MUST be performed.  Four messages are needed
  for completion.

  If for any local reason (e.g., management lock-out) and IPSP cannot
  respond to an ASP Up message with an ASP Up Ack message, it responds
  to an ASP Up message with an Error message with Reason "Refused -
  Management Blocking" and leaves the remote IPSP in the ASP-DOWN
  state.

4.3.4.2.  ASP Down Procedures

  The ASP will send an ASP Down message to an SGP when the ASP wishes
  to be removed from service in all Application Servers that it is a
  member and no longer receive any Connectionless or Connection -
  Oriented, SSNM or ASPTM messages.  This action MAY be initiated at
  the ASP by an M-ASP_DOWN request primitive from Layer Management or
  MAY be initiated automatically by an SUA management function.

  Whether the ASP is permanently removed from any AS is a function of
  configuration management.  In the case where the ASP previously used
  the Registration procedures (see Section 4.4.1) to register within
  Application Servers but has not deregistered from all of them prior
  to sending the ASP Down message, the SGP MUST consider the ASP as
  deregistered in all Application Servers that it is still a member.

  The SGP marks the ASP as ASP-DOWN, informs Layer Management with an
  M-ASP_Down indication primitive, and returns an ASP Down Ack message
  to the ASP.

  The SGP MUST send an ASP Down Ack message in response to a received
  ASP Down message from the ASP even if the ASP is already marked as
  ASP-DOWN at the SGP.

  At the ASP, the ASP Down Ack message received is not acknowledged.
  Layer Management is informed with an M-ASP_DOWN confirm primitive. If
  the ASP receives an ASP Down Ack without having sent an ASP Down
  message, the ASP should now consider itself as in the ASP-DOWN state.
  If the ASP was previously in the ASP-ACTIVE or ASP_INACTIVE state,
  the ASP should then initiate procedures to return itself to its
  previous state.

  When the ASP sends an ASP Down message it starts timer T(ack).  If
  the ASP does not receive a response to an ASP Down message within
  T(ack), the ASP MAY restart T(ack) and resend ASP Down messages until
  it receives an ASP Down Ack message.  T(ack) is provisioned, with a
  default of 2 seconds.  Alternatively, retransmission of ASP Down




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  messages MAY be put under control of Layer Management.  In this
  method, expiry of T(ack) results in an M-ASP_DOWN confirm primitive
  carrying a negative indication.

4.3.4.3.  ASP Active Procedures

  Anytime after the ASP has received an ASP Up Ack message from the SGP
  or IPSP, the ASP MAY send an ASP Active message to the SGP indicating
  that the ASP is ready to start processing traffic.  This action MAY
  be initiated at the ASP by an M-ASP_ACTIVE request primitive from
  Layer Management or MAY be initiated automatically by an SUA
  management function.  In the case where an ASP wishes to process the
  traffic for more than one Application Server across a common SCTP
  association, the ASP Active message(s) SHOULD contain a list of one
  or more Routing Contexts to indicate for which Application Servers
  the ASP Active message applies.  It is not necessary for the ASP to
  include all Routing Contexts of interest in a single ASP Active
  message, thus requesting to become active in all Routing Contexts at
  the same time.  Multiple ASP Active messages MAY be used to activate
  within the Application Servers independently, or in sets.  In the
  case where an ASP Active message does not contain a Routing Context
  parameter, the receiver must know, via configuration data, which
  Application Server(s) the ASP is a member.

  For the Application Servers that the ASP can be successfully
  activated, the SGP or IPSP responds with one or more ASP Active Ack
  messages, including the associated Routing Context(s) and reflecting
  any Traffic Mode Type value present in the related ASP Active
  message.  The Routing Context parameter MUST be included in the ASP
  Active Ack message(s) if the received ASP Active message contained
  any Routing Contexts.  Depending on any Traffic Mode Type request in
  the ASP Active message, or local configuration data if there is no
  request, the SGP moves the ASP to the correct ASP traffic state
  within the associated Application Server(s).  Layer Management is
  informed with an M-ASP_Active indication.  If the SGP or IPSP
  receives any Data messages before an ASP Active message is received,
  the SGP or IPSP MAY discard them.  By sending an ASP Active Ack
  message, the SGP or IPSP is now ready to receive and send traffic for
  the related Routing Context(s).  The ASP SHOULD NOT send Data or SSNM
  messages for the related Routing Context(s) before receiving an ASP
  Active Ack message, or it will risk message loss.

  Multiple ASP Active Ack messages MAY be used in response to an ASP
  Active message containing multiple Routing Contexts, allowing the SGP
  or IPSP to independently acknowledge the ASP Active message for
  different (sets of) Routing Contexts.  The SGP or IPSP MUST send an
  Error message ("Invalid Routing Context") for each Routing Context
  value that cannot be successfully activated.



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  In the case where an "out-of-the-blue" ASP Active message is received
  (i.e., the ASP has not registered with the SG or the SG has no static
  configuration data for the ASP), the message MAY be silently
  discarded.

  The SGP MUST send an ASP Active Ack message in response to a received
  ASP Active message from the ASP, if the ASP is already marked in the
  ASP-ACTIVE state at the SGP.

  At the ASP, the ASP Active Ack message received is not acknowledged.
  Layer Management is informed with an M-ASP_ACTIVE confirm primitive.
  It is possible for the ASP to receive Data message(s) before the ASP
  Active Ack message as the ASP Active Ack and Data messages from an SG
  or IPSP may be sent on different SCTP streams.  Message loss is
  possible, as the ASP does not consider itself in the ASP-ACTIVE state
  until reception of the ASP Active Ack message.

  When the ASP sends an ASP Active message it starts timer T(ack).  If
  the ASP does not receive a response to an ASP Active message within
  T(ack), the ASP MAY restart T(ack) and resend ASP Active messages
  until it receives an ASP Active Ack message.  T(ack) is provisioned,
  with a default of 2 seconds.  Alternatively, retransmission of ASP
  Active messages MAY be put under control of Layer Management.  In
  this method, expiry of T(ack) results in an M-ASP_ACTIVE confirm
  primitive carrying a negative indication.

  There are three modes of Application Server traffic handling in the
  SGP SUA layer: Override, Loadshare and Broadcast.  When included, the
  Traffic Mode Type parameter in the ASP Active message indicates the
  traffic-handling mode to be used in a particular Application Server.
  If the SGP determines that the mode indicated in an ASP Active
  message is unsupported or incompatible with the mode currently
  configured for the AS, the SGP responds with an Error message
  ("Unsupported / Invalid Traffic Handling Mode").  If the traffic-
  handling mode of the Application Server is not already known via
  configuration data, then the traffic-handling mode indicated in the
  first ASP Active message causing the transition of the Application
  Server state to AS-ACTIVE MAY be used to set the mode.

  In the case of an Override mode AS, reception of an ASP Active
  message at an SGP causes the (re)direction of all traffic for the AS
  to the ASP that sent the ASP Active message.  Any previously active
  ASP in the AS is now considered to be in state ASP-INACTIVE and
  SHOULD no longer receive traffic from the SGP within the AS.  The SGP
  or IPSP then MUST send a Notify message ("Alternate ASP Active") to
  the previously active ASP in the AS, and SHOULD stop traffic to/from





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  that ASP.  The ASP receiving this Notify MUST consider itself now in
  the ASP-INACTIVE state, if it is not already aware of this via
  inter-ASP communication with the Overriding ASP.

  In the case of a Loadshare mode AS, reception of an ASP Active
  message at an SGP or IPSP causes the direction of traffic to the ASP
  sending the ASP Active message, in addition to all the other ASPs
  that are currently active in the AS.  The algorithm at the SGP for
  loadsharing traffic within an AS to all the active ASPs is
  implementation dependent.  The algorithm could, for example, be round
  robin or based on information in the Data message (e.g., the SLS or
  SSN).

  An SGP or IPSP, upon reception of an ASP Active message for the first
  ASP in a Loadshare AS, MAY choose not to direct traffic to a newly
  active ASP until it determines that there are sufficient resources to
  handle the expected load (e.g., until there are "n" ASPs in state
  ASP-ACTIVE in the AS).

  All ASPs within a load-sharing mode AS must be able to process any
  Data message received for the AS, to accommodate any potential fail-
  over or rebalancing of the offered load.

  In the case of a Broadcast mode AS, reception of an ASP Active
  message at an SGP or IPSP causes the direction of traffic to the ASP
  sending the ASP Active message, in addition to all the other ASPs
  that are currently active in the AS.  The algorithm at the SGP for
  broadcasting traffic within an AS to all the active ASPs is a simple
  broadcast algorithm, where every message is sent to each of the
  active ASPs.  An SGP or IPSP, upon reception of an ASP Active message
  for the first ASP in a Broadcast AS, MAY choose not to direct traffic
  to a newly active ASP until it determines that there are sufficient
  resources to handle the expected load (e.g., until there are "n" ASPs
  in state ASP-ACTIVE in the AS).

  Whenever an ASP in a Broadcast mode AS becomes ASP-ACTIVE, the SGP
  MUST tag the first DATA message broadcast in each traffic flow with a
  unique Correlation Id parameter.  The purpose of this Correlation Id
  is to permit the newly active ASP to synchronize its processing of
  traffic in each traffic flow with the other ASPs in the broadcast
  group.










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4.3.4.3.1.  IPSP Considerations

  Either of the IPSPs can initiate communication.  When an IPSP
  receives an ASP Active, it should mark the peer as ASP-ACTIVE and
  return an ASP Active Ack message.  An ASP receiving an ASP Active Ack
  message may mark the peer as ASP-Active, if it is not already in the
  ASP-ACTIVE state.

  Alternatively, when using IPSP DE model, an interchange of ASP Active
  messages from each end MUST be performed.  Four messages are needed
  for completion.

4.3.4.4.  ASP Inactive Procedures

  When an ASP wishes to withdraw from receiving traffic within an AS,
  or the ASP wants to initiate the process of deactivation, the ASP
  sends an ASP Inactive message to the SGP or IPSP.

  An ASP Inactive message MUST be always responded by the peer
  (although other messages may be sent in the middle):

  -  If the corresponding RK is registered (statically or dynamically),
     the peer should respond with an ASP Inactive Ack message.

  -  If the RK is not registered, or the RC information is not valid,
     the peer must respond with an ERROR message with Error Code =
     "Invalid Routing Context".

  -  If the RC is missing and its specification is needed according to
     the used configuration, the peer must respond with an ERROR
     message with Error Code = "No Configured AS for ASP".

  The action of sending the ASP Inactive message MAY be initiated at
  the ASP by an M-ASP_INACTIVE request primitive from Layer Management
  or MAY be initiated automatically by an SUA management function.  In
  the case where an ASP is processing the traffic for more than one
  Application Server across a common SCTP association, the ASP Inactive
  message contains one or more Routing Contexts to indicate for which
  Application Servers the ASP Inactive message applies.

  In the case where an ASP Inactive message does not contain a Routing
  Context parameter, the receiver must know, via configuration data,
  which Application Servers the ASP is a member and move the ASP to the
  ASP-INACTIVE state in each all Application Servers.

  In the case of an Override mode AS, where another ASP has already
  taken over the traffic within the AS with an ASP Active ("Override")
  message, the ASP that sends the ASP Inactive message is already



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  considered by the SGP to be in state ASP-INACTIVE.  An ASP Inactive
  Ack message is sent to the ASP, after ensuring that all traffic is
  stopped to the ASP.

  In the case of a Loadshare mode AS, the SGP moves the ASP to the
  ASP-INACTIVE state and the AS traffic is reallocated across the
  remaining ASPs in the state ASP-ACTIVE, as per the loadsharing
  algorithm currently used within the AS.  A Notify message
  ("Insufficient ASP resources active in AS") MAY be sent to all
  inactive ASPs, if required.  An ASP Inactive Ack message is sent to
  the ASP after all traffic is halted and Layer Management is informed
  with an M-ASP_INACTIVE indication primitive.

  In the case of a Broadcast mode AS, the SGP moves the ASP to the
  ASP-INACTIVE state and the AS traffic is broadcast only to the
  remaining ASPs in the state ASP-ACTIVE.  A Notify message
  ("Insufficient ASP resources active in AS") MAY be sent to all
  inactive ASPs, if required.  An ASP Inactive Ack message is sent to
  the ASP after all traffic is halted and Layer Management is informed
  with an M-ASP_INACTIVE indication primitive.

  Multiple ASP Inactive Ack messages MAY be used in response to an ASP
  Inactive message containing multiple Routing Contexts, allowing the
  SGP or IPSP to independently acknowledge for different (sets of)
  Routing Contexts.  The SGP or IPSP sends an Error message ("Invalid
  Routing Context") message for each invalid or not configured Routing
  Context value in a received ASP Inactive message.

  The SGP MUST send an ASP Inactive Ack message in response to a
  received ASP Inactive message from the ASP and the ASP is already
  marked as ASP-INACTIVE at the SGP.

  At the ASP, the ASP Inactive Ack message received is not
  acknowledged.  Layer Management is informed with an M-ASP_INACTIVE
  confirm primitive.  If the ASP receives an ASP Inactive Ack without
  having sent an ASP Inactive message, the ASP should now consider
  itself as in the ASP-INACTIVE state.  If the ASP was previously in
  the ASP-ACTIVE state, the ASP should then initiate procedures to
  return itself to its previous state.  When the ASP sends an ASP
  Inactive message it starts timer T(ack).  If the ASP does not receive
  a response to an ASP Inactive message within T(ack), the ASP MAY
  restart T(ack) and resend ASP Inactive messages  until it receives an
  ASP Inactive Ack message.  T(ack) is provisioned, with a default of 2
  seconds.  Alternatively, retransmission of ASP Inactive messages MAY
  be put under control of Layer Management.  In this method, expiry of
  T(ack) results in a M-ASP_Inactive confirm primitive carrying a
  negative indication.




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  If no other ASPs in the Application Server are in the state ASP-
  ACTIVE, the SGP MUST send a Notify message ("AS-Pending") to all of
  the ASPs in the AS which are in the state ASP-INACTIVE.  The SGP
  SHOULD start buffering the incoming messages for T(r) seconds, after
  which messages MAY be discarded.  T(r) is configurable by the network
  operator.  If the SGP receives an ASP Active message from an ASP in
  the AS before expiry of T(r), the buffered traffic is directed to
  that ASP and the timer is cancelled.  If T(r) expires, the AS is
  moved to the AS-INACTIVE state.

4.3.4.4.1.  IPSP Considerations

  An IPSP may be considered in the ASP-INACTIVE state by a remote IPSP
  after an ASP Inactive or ASP Inactive Ack message has been received
  from it.

  Alternatively, when using IPSP DE model, an interchange of ASP
  Inactive messages from each end MUST be performed.  Four messages are
  needed for completion.

4.3.4.5.  Notify Procedures

  A Notify message reflecting a change in the AS state MUST be sent to
  all ASPs in the AS, except those in the ASP-DOWN state, with
  appropriate Status Information and any ASP Identifier of the failed
  ASP.  At the ASP, Layer Management is informed with an M-NOTIFY
  indication primitive.  The Notify message must be sent whether the AS
  state change was a result of an ASP failure or reception of an ASP
  State management (ASPSM) / ASP Traffic Management (ASPTM) message.
  In the second case, the Notify message MUST be sent after any ASP
  State or Traffic Management related acknowledgement messages  (e.g.,
  ASP Up Ack, ASP Down Ack, ASP Active Ack, or ASP Inactive Ack).

  In the case where a Notify ("AS-PENDING") message is sent by an SGP
  that now has no ASPs active to service the traffic, or where a Notify
  ("Insufficient ASP resources active in AS") message MUST be sent in
  the Loadshare or Broadcast mode, the Notify message does not
  explicitly compel the ASP(s) receiving the message to become active.
  The ASPs remain in control of what (and when) traffic action is
  taken.

  In the case where a Notify message does not contain a Routing Context
  parameter, the receiver must know, via configuration data, of which
  Application Servers the ASP is a member and take the appropriate
  action in each AS.






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4.3.4.5.1.  IPSP Considerations (NTFY)

  Notify works in the same manner as in the SG-AS case.  One of the
  IPSPs can send this message to any remote IPSP that is not in the
  ASP-DOWN state.

4.3.4.6.  Heartbeat Procedures

  The optional Heartbeat procedures MAY be used when operating over
  transport layers that do not have their own heartbeat mechanism for
  detecting loss of the transport association (i.e., other than SCTP).

  Either SUA peer may optionally send Heartbeat messages periodically,
  subject to a provisioned timer T(beat).  Upon receiving a Heartbeat
  message, the SUA peer MUST respond with a Heartbeat Ack message.

  If no Heartbeat Ack message (or any other SUA message) is received
  from the SUA peer within 2*T(beat), the remote SUA peer is considered
  unavailable.  Transmission of Heartbeat messages is stopped and the
  signalling process SHOULD attempt to reestablish communication if it
  is configured as the client for the disconnected SUA peer.

  The Heartbeat message may optionally contain an opaque Heartbeat Data
  parameter that MUST be echoed back unchanged in the related Heartbeat
  Ack message.  The sender, upon examining the contents of the returned
  Heartbeat Ack message, MAY choose to consider the remote SUA peer as
  unavailable.  The contents/format of the Heartbeat Data parameter is
  implementation-dependent and only of local interest to the original
  sender.  The contents may be used, for example, to support a
  Heartbeat sequence algorithm (to detect missing Heartbeats), and/or a
  timestamp mechanism (to evaluate delays).

  Note: Heartbeat related events are not shown in Figure 2 "ASP state
  transition diagram".

4.4.  Routing Key Management Procedures

4.4.1.  Registration

  An ASP MAY dynamically register with an SGP as an ASP within an
  Application Server using the REG REQ message.  A Routing Key
  parameter in the REG REQ message specifies the parameters associated
  with the Routing Key.

  The SGP examines the contents of the received Routing Key parameter
  and compares it with the currently provisioned Routing Keys.  If the
  received Routing Key matches an existing SGP Routing Key entry, and
  the ASP is not currently included in the list of ASPs for the related



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  Application Server, the SGP MAY authorize the ASP to be added to the
  AS.  Or, if the Routing Key does not currently exist and the received
  Routing Key data is valid and unique, an SGP supporting dynamic
  configuration MAY authorize the creation of a new Routing Key and
  related Application Server and add the ASP to the new AS.  In either
  case, the SGP returns a Registration Response message to the ASP,
  containing the same Local-RK-Identifier as provided in the initial
  request, and a Registration Result "Successfully Registered".  A
  unique Routing Context value assigned to the SGP Routing Key is
  included.  The method of Routing Context value assignment at the SGP
  is implementation dependent but must be guaranteed to be unique for
  each Application Server or Routing Key supported by the SGP.  If the
  SGP determines that the received Routing Key data is invalid, or
  contains invalid parameter values, the SGP returns a Registration
  Response message to the ASP, containing a Registration Result "Error
  - Invalid Routing Key", "Error - Invalid DPC", "Error - Invalid
  Network Appearance" as appropriate.

  If the SGP does not support the registration procedure, the SGP
  returns an Error message to the ASP, with an error code of
  "Unsupported Message Type".

  If the SGP determines that a unique Routing Key cannot be created,
  the SGP returns a Registration Response message to the ASP, with a
  Registration Status of "Error - Cannot Support Unique Routing".  An
  incoming signalling message received at an SGP should not match
  against more than one Routing Key.

  If the SGP does not authorize the registration request, the SGP
  returns a REG RSP message to the ASP containing the Registration
  Result "Error - Permission Denied".

  If an SGP determines that a received Routing Key does not currently
  exist and the SGP does not support dynamic configuration, the SGP
  returns a Registration Response message to the ASP, containing a
  Registration Result "Error - Routing Key not Currently Provisioned".

  If an SGP determines that a received Routing Key does not currently
  exist and the SGP supports dynamic configuration but does not have
  the capacity to add new Routing Key and Application Server entries,
  the SGP returns a Registration Response message to the ASP,
  containing a Registration Result "Error - Insufficient Resources".

  If an SGP determines that one or more of the Routing Key parameters
  are not supported for the purpose of creating new Routing Key
  entries, the SGP returns a Registration Response message to the ASP,





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  containing a Registration Result "Error - Unsupported RK parameter
  field".  This result MAY be used if, for example, the SGP does not
  support RK Address parameter.

  A Registration Response "Error - Unsupported Traffic Handling Mode"
  is returned if the Routing Key in the REG REQ contains a Traffic
  Handling Mode that is inconsistent with the presently configured mode
  for the matching Application Server.

  An ASP MAY register multiple Routing Keys at once by including a
  number of Routing Key parameters in a single REG REQ message.  The
  SGP MAY respond to each registration request in a single REG RSP
  message, indicating the success or failure result for each Routing
  Key in a separate Registration Result parameter.  Alternatively the
  SGP MAY respond with multiple REG RSP messages, each with one or more
  Registration Result parameters.  The ASP uses the Local-RK-Identifier
  parameter to correlate the requests with the responses.

  An ASP MAY modify an existing Routing Key by including a Routing
  Context parameter in the REG REQ.  If the SGP determines that the
  Routing Context applies to an existing Routing Key, the SG MAY adjust
  the existing Routing Key to match the new information provided in the
  Routing Key parameter.  A Registration Response "Routing Key Change
  Refused" is returned if the SGP does not accept the modification of
  the Routing Key.

  Upon successful registration of an ASP in an AS, the SGP can now send
  related SS7 Signalling Network Management messaging, if this did not
  previously start upon the ASP transitioning to state ASP-INACTIVE.

4.4.2.  Deregistration

  An ASP MAY dynamically deregister with an SGP as an ASP within an
  Application Server using the DEREG REQ message.  A Routing Context
  parameter in the DEREG REQ message specifies which Routing Keys to
  deregister.  An ASP SHOULD move to the ASP-INACTIVE state for an
  Application Server before attempting to deregister the Routing Key
  (i.e., deregister after receiving an ASP Inactive Ack).  Also, an ASP
  SHOULD deregister from all Application Servers that it is a member
  before attempting to move to the ASP-Down state.

  The SGP examines the contents of the received Routing Context
  parameter and validates that the ASP is currently registered in the
  Application Server(s) related to the included Routing Context(s).  If
  validated, the ASP is deregistered as an ASP in the related
  Application Server.





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  The deregistration procedure does not necessarily imply the deletion
  of Routing Key and Application Server configuration data at the SGP.
  Other ASPs may continue to be associated with the Application Server,
  in which case the Routing Key data SHOULD NOT be deleted.  If a
  Deregistration results in no more ASPs in an Application Server, an
  SGP MAY delete the Routing Key data.

  The SGP acknowledges the deregistration request by returning a DEREG
  RSP message to the requesting ASP.  The result of the deregistration
  is found in the Deregistration Result parameter, indicating success
  or failure with cause.

  An ASP MAY deregister multiple Routing Contexts at once by including
  a number of Routing Contexts in a single DEREG REQ message.  The SGP
  MAY respond to each deregistration request in a single DEREG RSP
  message, indicating the success or failure result for each Routing
  Context in a separate Deregistration Result parameter.

4.4.3.  IPSP Considerations (REG/DEREG)

  The Registration/Deregistration procedures work in the IPSP cases in
  the same way as in AS-SG cases.  An IPSP may register an RK in the
  remote IPSP.  An IPSP is responsible for deregistering the RKs that
  it has registered.

4.5.  Availability and/or Congestion Status of SS7 Destination Support

4.5.1.  At an SGP

  On receiving a N-STATE, N-PCSTATE and N-INFORM indication primitive
  from the nodal interworking function at an SGP, the SGP SUA layer
  will send a corresponding SS7 Signalling Network Management (SNM)
  DUNA, DAVA, SCON, or DUPU message (see Section 3.4) to the SUA peers
  at concerned ASPs.  The SUA layer must fill in various fields of the
  SNM messages consistently with the information received in the
  primitives.

  The SGP SUA layer determines the set of concerned ASPs to be informed
  based on the specific SS7 network for which the primitive indication
  is relevant.  In this way, all ASPs configured to send/receive
  traffic within a particular network appearance are informed.  If the
  SGP operates within a single SS7 network appearance, then all ASPs
  are informed.

  DUNA, DAVA, SCON, and DRST messages are sent sequentially and
  processed at the receiver in the order sent.  SCTP stream 0 SHOULD
  NOT be used.  The Unordered bit in the SCTP DATA chunk MAY be used
  for the SCON message.



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  Sequencing is not required for the DUPU or DAUD messages, which MAY
  be sent unordered.  SCTP stream 0 is used, with optional use of the
  Unordered bit in the SCTP DATA chunk.

4.5.2.  At an ASP

4.5.2.1.  Single SG Configurations

  At an ASP, upon receiving an SS7 Signalling Network Management (SSNM)
  message from the remote SUA Peer, the SUA layer invokes the
  appropriate primitive indications to the resident SUA-Users.  Local
  management is informed.

  In the case where a local event has caused the unavailability or
  congestion status of SS7 destinations, the SUA layer at the ASP
  SHOULD pass up appropriate indications in the primitives to the SUA
  User, as though equivalent SSNM messages were received.  For example,
  the loss of an SCTP association to an SGP may cause the
  unavailability of a set of SS7 destinations.  N-PCSTATE indication
  primitives to the SUA User are appropriate.

  Implementation Note: To accomplish this, the SUA layer at an ASP
  maintains the status of routes via the SG.

4.5.2.2.  Multiple SG Configurations

  At an ASP, upon receiving a Signalling Network Management message
  from the remote SUA Peer, the SUA layer updates the status of the
  affected route(s) via the originating SG and determines, whether or
  not the overall availability or congestion status of the effected
  destination(s) has changed.  If so, the SUA layer invokes the
  appropriate primitive indications to the resident SUA-Users.  Local
  management is informed.

4.5.3.  ASP Auditing

  An ASP may optionally initiate an audit procedure to inquire of an
  SGP the availability and, if the national congestion method with
  multiple congestion levels and message priorities is used, congestion
  status of an SS7 destination or set of destinations.  A Destination
  Audit (DAUD) message is sent from the ASP to the SGP requesting the
  current availability and congestion status of one or more SS7
  destinations or subsystems.

  The DAUD message MAY be sent unordered.  The ASP MAY send the DAUD in
  the following cases:





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  - Periodic.  A Timer originally set upon reception of a DUNA, SCON or
               DRST message has expired without a subsequent DAVA,
               DUNA, SCON or DRST message updating the
               availability/congestion status of the affected
               Destination Point Code.  The Timer is reset upon issuing
               a DAUD.  In this case the DAUD is sent to the SGP that
               originally sent the SSNM message.

  - Isolation. The ASP is newly ASP-ACTIVE or has been isolated from an
               SGP for an extended period.  The ASP MAY request the
               availability/congestion status of one or more SS7
               destinations to which it expects to communicate.

  Implementation Note:

     In the first of the cases above, the auditing procedure must not
     be invoked for the case of a received SCON message containing a
     congestion level value of "no congestion" or undefined" (i.e.,
     congestion Level = "0").  This is because the value indicates
     either congestion abatement or that the ITU MTP3 international
     congestion method is being used.  In the international congestion
     method, the MTP3 layer at the SGP does not maintain the congestion
     status of any destinations and therefore the SGP cannot provide
     any congestion information in response to the DAUD.  For the same
     reason, in the second of the cases above a DAUD message cannot
     reveal any congested destination(s).

  The SGP SHOULD respond to a DAUD message with the availability and
  congestion status of the subsystem.  The status of each SS7
  destination or subsystem requested is indicated in a DUNA message (if
  unavailable), a DAVA message (if available), or a DRST (if restricted
  and the SGP supports this feature).  If the SS7 destination or
  subsystem is available and congested, the SGP responds with an SCON
  message in addition to the DAVA message.  If the SS7 destination or
  subsystem is restricted and congested, the SGP responds with an SCON
  message in addition to the DRST.  If the SGP has no information on
  the availability / congestion status of the SS7 destination or
  subsystem, the SGP responds with a DUNA message, as it has no routing
  information to allow it to route traffic to this destination or
  subsystem.

  An SG MAY refuse to provide the availability or congestion status of
  a destination or subsystem if, for example, the ASP is not authorized
  to know the status of the destination or subsystem.  The SG MAY
  respond with an Error Message (Error Code = "Destination Status
  Unknown") or Error Message (Error Code = "Subsystem Status Unknown").





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4.6.  MTP3 Restart

  In the case where the MTP3 in the SG undergoes an MTP restart, event
  communication SHOULD be handled as follows:

  When the SG discovers SS7 network isolation, the SGPs send an
  indication to all concerned available ASPs (i.e., ASPs in the ASP-
  ACTIVE state) using DUNA messages for the concerned destinations.
  When the SG has completed the MTP Restart procedure, the SUA layer at
  the SGPs inform all concerned ASPs in the ASP-ACTIVE state of any
  available/restricted SS7 destinations using the DAVA/DRST message.
  No message is necessary for those destinations still unavailable
  after the restart procedure.

  When the SUA layer at an ASP receives a DUNA message indicating SS7
  destination unavailability at an SG, SCCP Users will receive an N-
  PCSTATE indication and will stop any affected traffic to this
  destination.  When the SUA receives a DAVA/DRST message, SCCP Users
  will receive an N-PCSTATE indication and can resume traffic to the
  newly available SS7 destination via this SGP, provided the ASP is in
  the ASP-ACTIVE state toward this SGP.

  The ASP MAY choose to audit the availability of unavailable
  destinations by sending DAUD messages.  This would be for example the
  case when an AS becomes active at an ASP and does not have current
  destination statuses.  If MTP restart is in progress at the SG, the
  SGP returns a DUNA message for that destination, even if it received
  an indication that the destination became available or restricted.

4.7.  SCCP - SUA Interworking at the SG

4.7.1.  Segmenting / Reassembly

  When it is expected that signalling messages will not fit into a PDU
  of the most restrictive transport technology used (e.g., 272-SIF of
  MTP3), then segmenting/reassembly could be performed at the SG, ASP
  or IPSP.  If the SG, ASP or IPSP is incapable of performing a
  necessary segmentation/reassembly, it can inform the peer of the
  failure using the appropriate error in a CLDR or RESRE/COERR message.

4.7.2.  Support for Loadsharing

  Within an AS (identified by RK/RC parameters) several loadsharing
  ASPs may be active.







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  However, to assure the correct processing of TCAP transactions or
  SCCP connections, the loadsharing scheme used at the SG must make
  sure that messages continuing or ending the transactions/connections
  arrive at the same ASP where the initial message (TC_Query, TC_Begin,
  CR) was sent to/received from.

  When the ASP can be identified uniquely based on RK parameters (e.g.,
  unique DPC or GT), loadsharing is not required.  When the ASPs in the
  AS share state or use an internal distribution mechanism, the SG must
  only take into account the in-sequence-delivery requirement.  In case
  of SCCP CO traffic, when the coupled approach is used, loadsharing of
  messages other than CR is not required.

  If these assumptions cannot be made, both SG and ASP should support
  the following general procedure in a loadsharing environment.

4.7.2.1.  Association Setup, ASP going active

  After association setup and registration, an ASP normally goes active
  for each AS it registered for.  In the ASPAC message, the ASP
  includes a TID and/or DRN Label Parameter, if applicable for the AS
  in question.  All the ASPs within the AS must specify a unique label
  at a fixed position in the TID or DRN parameter.  The same ASPAC
  message is sent to each SG used for interworking with the SS7
  network.

  The SG builds, per RK, a list of ASPs that have registered for it.
  The SG can now build up and update a distribution table for a certain
  Routing Context, any time the association is (re-)established and the
  ASP goes active.  The SG has to perform some trivial plausibility
  checks on the parameters:

  - Start and End parameters values are between 0 and 31 for TID.
  - Start and End parameters values are between 0 and 23 for DRN
  - 0 < (Start - End + 1) <= 16 (label length maximum 16-bit)
  - Start values are the same for each ASP within a RC
  - End values are the same for each ASP within a RC
  - TID and DRN Label values must be unique across the RC

  If any of these checks fail, the SG refuses the ASPAC request, with
  an error, "Invalid loadsharing label."










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4.7.3.  Routing and message distribution at the SG

4.7.3.1.  TCAP traffic

  Messages not containing a destination (or "responding") TID, i.e.,
  Query, Begin, Unidirectional, are loadshared among the available
  ASPs.  Any scheme permitting a fair load distribution among the ASPs
  is allowed (e.g., round robin).

  When a destination TID is present, the SG extracts the label and
  selects the ASP that corresponds with it.

  If an ASP is not available, the SG may generate (X)UDTS "routing
  failure", if the return option is used.

4.7.3.2.  SCCP Connection Oriented traffic

  Messages not containing a destination reference number (DRN), i.e., a
  Connection Request, MAY be loadshared among the available ASPs.  The
  load distribution mechanism is an implementation issue.  When a DRN
  is present, the SG extracts the label and selects the ASP that
  corresponds with it.  If an ASP is not available, the SG discards the
  message.

4.7.4.  Multiple SGs, SUA Relay Function

  It is important that each ASP send its unique label (within the AS)
  to each SGP.  For a better robustness against association failures,
  the SGs MAY cooperate to provide alternative routes toward an ASP.
  Mechanisms for SG cooperation/coordination are outside of the scope
  of this document.

5.  Examples of SUA Procedures

  The following sequence charts overview the procedures of SUA.  These
  are meant as examples, they do not, in and of themselves, impose
  additional requirements upon an instance of SUA.

5.1.  SG Architecture

  The sequences below outline logical steps for a variety of scenarios
  within a SG architecture.  Please note that these scenarios cover a
  Primary/Backup configuration.  Where there is a load-sharing
  configuration then the SGP can declare availability when 1 ASP issues
  ASPAC but can only declare unavailability when all ASPs have issued
  ASPIA.





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5.1.1.  Establishment of SUA connectivity

  The following is established before traffic can flow.

  Each node is configured (via MIB, for example) with the connections
  that need to be setup.

   ASP-a1            ASP-a2                SG                  SEP
  (Primary)           (Backup)
     |------Establish SCTP Association------|
                        |--Estab. SCTP Ass--|
                                            |--Align SS7 link---|
     +----------------ASP Up---------------->
     <--------------ASP Up Ack--------------+
                        +------ASP Up------->
                        <---ASP Up Ack------+
     +-------------ASP Active--------------->
     <----------ASP Active Ack--------------+
     <----------NTFY (ASP Active)-----------+
                        <-NTFY (ASP Active)-+
                                            +--------SSA-------->
                                            <--------SSA--------+
     <-----------------DAVA-----------------+
     +-----------------CLDT----------------->
                                            +--------UDT-------->

5.1.2.  Fail-over scenarios

  The following sequences address fail-over of SEP and ASP.

5.1.2.1.  SEP Fail-over

  The SEP knows that the SGP is 'concerned' about its availability.
  Similarly, the SGP knows that ASP-a1 is concerned about the SEPs
  availability.

    ASP-a1            ASP-a2                SG                  SEP
  (Primary)           (Backup)
                                             <--------SSP--------+
      <-----------------DUNA-----------------+
      +-----------------DAUD----------------->
                                             +--------SST-------->









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5.1.2.2.  Successful ASP Fail-over scenario

  The following is an example of a successful fail-over scenario, where
  there is a fail-over from ASP-a1 to ASP-a2, i.e., Primary to Backup.
  During the fail-over, the SGP buffers any incoming data messages from
  the SEP, forwarding them when the Backup becomes available.

    ASP-a1            ASP-a2                SG                  SEP
  (Primary)           (Backup)
      +-------------ASP Inactive------------->
      <-----------ASP Inactive ACK-----------+
      <--------------------NTFY (AS Pending)-+
                         <-NTFY (AS Pending)-+
                         +----ASP Active----->
                         <--ASP Active Ack---+
                         <-NTFY (AS Active)--+
      <----------NTFY (AS Active)------------+

5.1.2.3.  Unsuccessful ASP Fail-over scenario

    ASP-a1            ASP-a2                SG                  SEP
  (Primary)           (Backup)
      +-------------ASP Inactive------------->
      <-----------ASP Inactive ACK-----------+
      <--------------------NTFY (AS Pending)-+
                        <--NTFY (AS Pending)-+
            After some time elapses (i.e., timeout).
                                             +--------SSP-------->
                                             <--------SST--------+
      <-------------------NTFY (AS Inactive)-+
                        <-NTFY (AS Inactive)-+

5.2.  IPSP Examples

  The sequences below outline logical steps for a variety of scenarios
  within an IP-IP architecture.  Please note that these scenarios cover
  a Primary/Backup configuration.  Where there is a load-sharing
  configuration then the AS can declare availability when 1 ASP issues
  ASPAC but can only declare unavailability when all ASPs have issued
  ASPIA.

5.2.1.  Establishment of SUA connectivity

  The following shows an example establishment of SUA connectivity. In
  this example, each IPSP consists of an Application Server and two
  ASPs.  The following is established before SUA traffic can flow.  A
  connectionless flow is shown for simplicity.




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  Establish SCTP Connectivity - as per RFC 2960.  Note that SCTP
  connections are bidirectional.  The endpoint that establishes SCTP
  connectivity MUST also establish UA connectivity (see RFC 2960,
  section 5.2.1 for handling collisions) [2960].

  IP SEP A                                                  IP SEP B
  AS A                                                          AS B
  ASP-a1     ASP-a2                                 ASP-b2    ASP-b1

  [All ASPs are in the ASP-DOWN state]

  +-------------------------------ASP Up-------------------------->
  <-----------------------------ASP Up Ack------------------------+

                +--------------ASP Up--------------->
                <------------ASP Up Ack-------------+

  +---------------------------ACTIVE------------------------------->
  <-------------------------ACTIVE Ack-----------------------------+

  [Traffic can now flow directly between ASPs]

  +-----------------------------CLDT------------------------------->

5.2.2.  Fail-over scenarios

  The following sequences address fail-over of ASP.

5.2.2.1.  Successful ASP Fail-over scenario

  The following is an example of a successful fail-over scenario, where
  there is a fail-over from ASP-a1 to ASP-a2, i.e., Primary to Backup.
  Since data transfer passes directly between peer ASPs, ASP-b1 is
  notified of the fail-over of ASP-a1 and buffers outgoing data
  messages until ASP-a2 becomes available.

  IP SEP A                                                  IP SEP B
  ASP-a1     ASP-a2                                 ASP-b2    ASP-b1

  +-----------------------------ASP Inact------------------------>
  <---------------------------ASP Inact Ack----------------------+
             <---------------NTFY (ASP-a1 Inactive)--------------+
             +---------------------ASP Act----------------------->
             <-------------------ASP Act Ack---------------------+







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5.2.2.2.  Unsuccessful ASP Fail-over scenario

  The sequence is the same as 5.2.2.1 except that, since the backup
  fails to come in then, the Notify messages declaring the availability
  of the backup are not sent.

6.  Security Considerations

  The security considerations discussed for the 'Security
  Considerations for SIGTRAN Protocols' [3788] document apply to this
  document.

7.  IANA Considerations

7.1.  SCTP Payload Protocol ID

  IANA has assigned a SUA value for the Payload Protocol Identifier in
  the SCTP DATA chunk.  The following SCTP Payload Protocol Identifier
  is registered:

     SUA    "4"

  The SCTP Payload Protocol Identifier value "4" SHOULD be included in
  each SCTP DATA chunk, to indicate that the SCTP is carrying the SUA
  protocol.  The value "0" (unspecified) is also allowed but any other
  values MUST not be used.  This Payload Protocol Identifier is not
  directly used by SCTP but MAY be used by certain network entities to
  identify the type of information being carried in a DATA chunk.

  The User Adaptation peer MAY use the Payload Protocol Identifier, as
  a way of determining additional information about the data being
  presented to it by SCTP.

7.2.  Port Number

  IANA has registered SCTP Port Number 14001 for SUA.  It is
  recommended that SGPs use this SCTP port number for listening for new
  connections.  SGPs MAY also use statically configured SCTP port
  numbers instead.

7.3.  Protocol Extensions

  This protocol may also be extended through IANA in three ways:

  -  Through definition of additional message classes.
  -  Through definition of additional message types.
  -  Through definition of additional message parameters.




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  The definition and use of new message classes, types and parameters
  is an integral part of SIGTRAN adaptation layers.  Thus, these
  extensions are assigned by IANA through an IETF Consensus action as
  defined in [2434].

  The proposed extension MUST in no way adversely affect the general
  working of the protocol.

  A new registry has been created by IANA to allow the protocol to be
  extended.

7.3.1.  IETF Defined Message Classes

  The documentation for a new message class MUST include the following
  information:

  (a) A long and short name for the message class;
  (b) A detailed description of the purpose of the message class.

7.3.2.  IETF Defined Message Types

  Documentation of the message type MUST contain the following
  information:

  (a) A long and short name for the new message type;
  (b) A detailed description of the structure of the message.
  (c) A detailed definition and description of intended use of each
      field within the message.
  (d) A detailed procedural description of the use of the new message
      type within the operation of the protocol.
  (e) A detailed description of error conditions when receiving this
      message type.

  When an implementation receives a message type which it does not
  support, it MUST respond with an Error (ERR) message, with an Error
  Code = Unsupported Message Type.

7.3.4.  IETF-defined TLV Parameter Extension

  Documentation of the message parameter MUST contain the following
  information:

  (a) Name of the parameter type.
  (b) Detailed description of the structure of the parameter field.
      This structure MUST conform to the general type-length-value
      format described earlier in the document.
  (c) Detailed definition of each component of the parameter value.




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  (d) Detailed description of the intended use of this parameter type,
      and an indication of whether and under what circumstances
      multiple instances of this parameter type may be found within the
      same message type.

8.  Timer Values

  Ta                                      2 seconds
  Tr                                      2 seconds
  T(ack)                                  2 seconds
  T(ias)    Inactivity Send timer         7 minutes
  T(iar)    Inactivity Receive timer      15 minutes
  T(beat)   Heartbeat Timer               30 seconds

9.  Acknowledgements

  The authors would like to thank (in alphabetical order) Richard
  Adams, Javier Pastor-Balbas, Andrew Booth, Martin Booyens, F.
  Escobar, S. Furniss Klaus Gradischnig, Miguel A. Garcia, Marja-Liisa
  Hamalainen, Sherry Karl, S. Lorusso, Markus Maanoja, Sandeep Mahajan,
  Ken Morneault, Guy Mousseau, Chirayu Patel, Michael Purcell, W.
  Sully, Michael Tuexen, Al Varney, Tim Vetter, Antonio Villena, Ben
  Wilson, Michael Wright and James Yu for their insightful comments and
  suggestions.

10.  References

10.1.  Normative References

  [1123]         Braden, R., Ed., "Requirements for Internet Hosts -
                 Application and Support", STD 3, RFC 1123, October
                 1989.

  [2119]         Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.

  [2960]         Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
                 Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M.,
                 Zhang, L., and V. Paxson, "Stream Control Transmission
                 Protocol", RFC 2960, October 2000.

  [3629]         Yergeau, F., "UTF-8, a transformation format of ISO
                 10646", STD 63, RFC 3629, November 2003.

  [3788]         Loughney, J., Tuexen, M., Ed., and J. Pastor-Balbas,
                 "Security Considerations for Signaling Transport
                 (SIGTRAN) Protocols", RFC 3788, June 2004.




Loughney, et al.            Standards Track                   [Page 123]

RFC 3868                          SUA                       October 2004


  [ANSI SCCP]    ANSI T1.112 "Signalling System Number 7 - Signalling
                 Connection Control Part".

  [ITU SCCP]     ITU-T Recommendations Q.711-714, "Signalling System
                 No. 7 (SS7) - Signalling Connection Control Part
                 (SCCP)."  ITU-T Telecommunication Standardization
                 Sector of ITU, formerly CCITT, Geneva (July 1996).

10.2.  Informative References

  [2434]         Narten, T. and H. Alvestrand, "Guidelines for Writing
                 an IANA Considerations Section in RFCs", BCP 26, RFC
                 2434, October 1998.

  [2719]         Ong, L., Rytina, I., Garcia, M., Schwarzbauer, H.,
                 Coene, L., Lin, H., Juhasz, I., Holdrege, M., and C.
                 Sharp, "Framework Architecture for Signalling
                 Transport", RFC 2719, October 1999.

  [3761]         Falstrom, P. and M. Mealling, "The E.164 to Uniform
                 Resource Identifiers (URI) Dynamic Delegation
                 Discovery System (DDDS) Application (ENUM)", RFC 3761,
                 April 2004.

  [ANSI TCAP]    ANSI T1.114 'Signalling System Number 7 - Transaction
                 Capabilities Application Part'

  [ITU TCAP]     ITU-T Recommendation Q.771-775 'Signalling System No.
                 7 SS7) - Transaction Capabilities (TCAP).'

  [RANAP]        3G TS 25.413 V3.5.0 (2001-03) 'Technical Specification
                 3rd Generation Partnership Project; Technical
                 Specification Group Radio Access Network; UTRAN Iu
                 Interface RANAP Signalling'

















Loughney, et al.            Standards Track                   [Page 124]

RFC 3868                          SUA                       October 2004


Appendix A.  Signalling Network Architecture

A.1.  Generalized Peer-to-Peer Network Architecture

  Figure 3 shows an example network architecture that can support
  robust operation and fail-over.  There needs to be some management
  resources at the AS to manage traffic.

  ***********
  *   AS1   *
  * +-----+ * SCTP Associations
  * |ASP1 +-------------------+
  * +-----+ *                 |                   ***********
  *         *                 |                   *   AS3   *
  * +-----+ *                 |                   * +-----+ *
  * |ASP2 +-----------------------------------------+ASP1 | *
  * +-----+ *                 |                   * +-----+ *
  *         *                 |                   *         *
  * +-----+ *                 |                   * +-----+ *
  * |ASP3 | *            +--------------------------+ASP2 | *
  * +-----+ *            |    |                   * +-----+ *
  ***********            |    |                   ***********
                         |    |
  ***********            |    |                   ***********
  *   AS2   *            |    |                   *   AS4   *
  * +-----+ *            |    |                   * +-----+ *
  * |ASP1 +--------------+    +---------------------+ASP1 | *
  * +-----+ *                                     * +-----+ *
  *         *                                     *         *
  * +-----+ *                                     * +-----+ *
  * |ASP2 +-----------------------------------------+ASP1 | *
  * +-----+ *                                     * +-----+ *
  *         *                                     ***********
  * +-----+ *
  * |ASP3 | *
  * +-----+ *
  *         *
  ***********

             Figure 3: Generalized Architecture

  In this example, the Application Servers are shown residing within
  one logical box, with ASPs located inside.  In fact, an AS could be
  distributed among several hosts.  In such a scenario, the host should
  share state as protection in the case of a failure.  This is out of
  scope of this protocol.  Additionally, in a distributed system, one
  ASP could be registered to more than one AS.  This document should
  not restrict such systems - though such a case in not specified.



Loughney, et al.            Standards Track                   [Page 125]

RFC 3868                          SUA                       October 2004


A.2.  Signalling Gateway Network Architecture

  When interworking between SS7 and IP domains is needed, the SGP acts
  as the gateway node between the SS7 network and the IP network.  The
  SGP will transport SCCP-user signalling traffic from the SS7 network
  to the IP-based signalling nodes (for example IP-resident Databases).
  The Signalling Gateway can be considered as a group of Application
  Servers with additional functionality to interface toward an SS7
  network.

  The SUA protocol should be flexible enough to allow different
  configurations and transport technology to allow the network
  operators to meet their operation, management and performance
  requirements.

  An ASP may be connected to multiple SGPs (see figure 4).  In such a
  case, a particular SS7 destination may be reachable via more than SG,
  therefore, more than one route.  Given that proper SLS selection,
  loadsharing, and SG selection based on point code availability is
  performed at the ASP, it will be necessary for the ASP to maintain
  the status of each distant SGPs to which it communicates on the basis
  of the SG through which it may route.





























Loughney, et al.            Standards Track                   [Page 126]

RFC 3868                          SUA                       October 2004


  Signalling Gateway
                           SCTP Associations
     +----------+                                       **************
     | SG1      |                                       *  AS3       *
     | ******** |                                       *  ********  *
     | * SGP11+--------------------------------------------+ ASP1 *  *
     | ******** |                                 /     *  ********  *
     | ******** |                                 |     *  ********  *
     | * SGP12+--------------------------------------------+ ASP2 *  *
     | ******** |                   \           / |     *  ********  *
     +----------+                    \          | |     *      .     *
                                      \         | |     *      .     *
     +----------                       \        | |     *      .     *
     | SG2      |                       \       | |     *      .     *
     | ******** |                        \      | |     *  ********  *
     | * SGP21+---------------------------------+-+     *  * ASPN *  *
     | ******** |                          \            *  ********  *
     | ******** |                           \           **************
     | * SGP22+---+--+                       \
     | ******** | |  |                        \         **************
     +----------+ |  |                         \        *  AS4       *
                  |  |                          \       *  ********  *
                  |  +-------------------------------------+ ASP1 *  *
                  |                                     *  ********  *
                  |                                     *      .     *
                  |                                     *      .     *
                  |                                     *            *
                  |                                     *  ********  *
                  +----------------------------------------+ ASPn *  *
                                                        *  ********  *
                                                        **************

               Figure 4: Signalling Gateway Architecture

  The pair of SGs can either operate as replicated endpoints or as
  replicated relay points from the SS7 network point of view.

  Replicated endpoints: the coupling between the SGs and the ASPs when
  the SGs act as replicated endpoints is an implementation issue.

  Replicated relay points: in normal circumstances, the path from SEP
  to ASP will always go via the same SGP when in-sequence-delivery is
  requested.  However, linkset failures may cause MTP to reroute to the
  other SG.







Loughney, et al.            Standards Track                   [Page 127]

RFC 3868                          SUA                       October 2004


A.3.  Signalling Gateway Message Distribution Recommendations

A.3.1.  Connectionless Transport

  By means of configuration, the SG knows the local SCCP-user is
  actually represented by an AS, and serviced by a set of ASPs working
  in n+k redundancy mode.  An ASP is selected and a CLDT message is
  sent on the appropriate SCTP association/stream.

  The selection criterion can be based on a round robin mechanism, or
  any other method that guarantees a balanced loadsharing over the
  active ASPs.  However, when TCAP messages are transported, load
  sharing is only possible for the first message in a TCAP dialogue
  (TC_Begin, TC_Query, TC_Unidirectional).  All other TCAP messages in
  the same dialogue are sent to the same ASP that was selected for the
  first message, unless the ASPs are able to share state and maintain
  sequenced delivery.  To this end, the SGP needs to know the TID
  allocation policy of the ASPs in a single AS:

  -  State sharing
  -  Fixed range of TIDs per ASP in the AS

  This information may be provisioned in the SG, or may be dynamically
  exchanged via the ASP_Active message.

  An example for an INAP/TCAP message exchange between SEP and ASP is
  given below.

  Address information in CLDT message (e.g., TC_Query) from SGP to ASP,
  with association ID = SG-ASP, Stream ID based on sequence control and
  possibly other parameters, e.g., OPC:

  -  Routing Context: based on SS7 Network ID and AS membership, so
     that the message can be transported to the correct ASP.
  -  Source address: valid combination of SSN, PC and GT, as needed for
     back routing to the SEP.
  -  Destination address: at least SSN, to select the SCCP/SUA-user at
     the ASP.

  Address information in CLDT message (e.g., TC_Response) from ASP to
  SG, with association ID = ASP-SG, stream ID selected by
  implementation dependent means with regards to in-sequence-delivery:

  -  Routing Context: as received in previous message.
  -  Source address: unique address provided so that when used as the
     SCCP called party address in the SEP, it must yield the same AS,
     the SSN might be sufficient.




Loughney, et al.            Standards Track                   [Page 128]

RFC 3868                          SUA                       October 2004


  -  Destination address: copied from source address in received CLDT
     message.

  Further messages from the SEP belonging to the same TCAP transaction
  will now reach the same ASP.

A.3.2.  Connection-Oriented Transport

  Further messages for this connection are routed on DPC in the SS7
  connection section (MTP routing label), and on IP address in the IP
  connection section (SCTP header).  No other routing information is
  present in the SCCP or SUA messages themselves.  Resources are kept
  within the SG to forward messages from one section to another and to
  populate the MTP routing label or SCTP header, based on the
  destination local reference of these messages (Connect Confirm, Data
  Transfer, etc.)

  This means that in the SG, two local references are allocated, one
  3-byte value used for the SS7 section and one 4-byte value for the IP
  section.  Also a resource containing the connection data for both
  sections is allocated, and either of the two local references can be
  used to retrieve this data e.g., for an incoming DT1 or CODT, for
  example.

Authors' Addresses

  John Loughney
  Nokia Research Center
  PO Box 407
  FIN-00045 Nokia Group
  Finland

  EMail: [email protected]


  Greg Sidebottom
  Signatus Technologies
  Kanata, Ontario
  Canada

  EMail: [email protected]










Loughney, et al.            Standards Track                   [Page 129]

RFC 3868                          SUA                       October 2004


  Lode Coene
  Siemens n.v.
  Atealaan 34
  B-2200 Herentals
  Belgium

  Phone: +32-14-252081
  EMail: [email protected]


  Gery Verwimp
  Siemens n.v.
  34 Atealaan
  PO 2200
  Herentals
  Belgium

  Phone: +32 14 25 3424
  EMail: [email protected]


  Joe Keller
  Tekelec
  5200 Paramount Parkway
  Morrisville, NC 27560
  USA

  EMail: [email protected]


  Brian Bidulock
  OpenSS7 Corporation
  1469 Jeffreys Crescent
  Edmonton, AB  T6L 6T1
  Canada

  Phone: +1 780 490 1141
  EMail: [email protected]













Loughney, et al.            Standards Track                   [Page 130]

RFC 3868                          SUA                       October 2004


Full Copyright Statement

  Copyright (C) The Internet Society (2004).  This document is subject
  to the rights, licenses and restrictions contained in BCP 78, and
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  This document and the information contained herein are provided on an
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  ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
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Acknowledgement

  Funding for the RFC Editor function is currently provided by the
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