Network Working Group                                 P. Newman, Ipsilon
Request for Comments: 1954                         W. L. Edwards, Sprint
Category: Informational                               R. Hinden, Ipsilon
                                                    E. Hoffman, Ipsilon
                                                 F. Ching Liaw, Ipsilon
                                                       T. Lyon, Ipsilon
                                                   G. Minshall, Ipsilon
                                                               May 1996


         Transmission of Flow Labelled IPv4 on ATM Data Links
                         Ipsilon Version 1.0

Status of this Memo

  This document provides information for the Internet community.  This
  memo does not specify an Internet standard of any kind.  Distribution
  of this memo is unlimited.

IESG Note:

  This note documents a private protocol for IPv4-based flows.  This
  protocol is NOT the product of an IETF working group nor is it a
  standards track document. It has not necessarily benefited from the
  widespread and in depth community review that standards track
  documents receive.

Abstract

  This document specifies the manner for transmitting IPv4 datagrams
  over an ATM data link, both in a default manner and in the presence
  of flow labelling via Ipsilon Flow Management Protocol [IFMP].

Table of Contents

  Introduction....................................................2
  1. Labels.......................................................2
  2. Default Encapsulation........................................2
  3. Flow Type 0 Encapsulation....................................3
  4. Flow Type 1 Encapsulation....................................4
  5. Flow Type 2 Encapsulation....................................5
  References......................................................7
  Security Considerations.........................................7
  Authors' Addresses..............................................7







Newman, et. al.              Informational                      [Page 1]

RFC 1954               Flow Labelled IPv4 on ATM                May 1996


Introduction

  This document specifies the manner for transmitting IPv4 datagrams
  over an ATM data link, both in a default manner and in the presence
  of flow labelling via Ipsilon Flow Management Protocol [IFMP].  ATM
  specific functions such as OAM cells, the CLP bit, and ABR RM cells
  are not used.  There are no reserved VCIs other than VPI = 0, VCI =
  0, which indicates an unassigned cell; and VPI = 0, VCI = 15, which
  is used for the default encapsulation.  IFMP messages must be sent
  using the default encapsulation.

1. Labels

  Labels, as carried by IFMP, are realized on an ATM data link as
  specific VPI/VCIs.  The format of the Label field for ATM labels is:

   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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |Reservd|          VPI          |             VCI               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The low order 16 bits of the label correspond to the VCI, with the
  least significant bit of the Label field corresponding to the least
  significant bit of the VCI.  If the link cannot support a full 16 bit
  VCI the unused bits of the VCI must be the most significant bits and
  they must be set to zero.

  The next 12 higher order bits of the label correspond to the VPI,
  with the least significant of these bits corresponding to the least
  significant bit of the VPI.  If the link cannot support a full 12 bit
  VPI, then the unused bits of the VPI must be the most significant
  bits and they must be set to zero.  The most significant four bits of
  the label are reserved.  They should be set to zero by the sender and
  ignored by the receiver.

2. Default Encapsulation

  The default encapsulation for IPv4 packets on ATM data links is the
  LLC/SNAP encapsulation specified in section 4.1 "LLC encapsulation
  for routed protocols" of RFC 1483 [RFC1483].  Such frames begin with
  the octets 0xAA 0xAA 0x03 0x00 0x00 0x00 0x08 0x00 (the LLC/SNAP
  header for IPv4).  The LLC/SNAP header is prefixed to the IP datagram
  and the entire packet is encapsulated within the payload of an AAL-5
  CPCS-PDU as specified in RFC 1483 and illustrated below:






Newman, et. al.              Informational                      [Page 2]

RFC 1954               Flow Labelled IPv4 on ATM                May 1996


   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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |               LLC (0xAA-AA-03)                |               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |
  |                   SNAP (0x00-00-00-08-00)                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  ~                         IPv4 Datagram                         ~
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                   Pad (0 - 47 octets)                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  +               AAL-5 CPCS-PDU Trailer (8 octets)               +
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The maximum transmission unit (MTU) of an IPv4 datagram using the
  default encapsulation is 1500 octets.

  Frames using the default encapsulation are sent to: VPI = 0, VCI =
  15.

3. Flow Type 0 Encapsulation

  All IPv4 frames using Flow Type 0 are encapsulated within the payload
  of an AAL-5 CPCS-PDU.  This is the null encapsulation of section 5.1
  "VC based multiplexing of routed protocols" from RFC 1483 [RFC1483].
  There is no LLC/SNAP header.  The first octet of the frame
  corresponds to the first octet of the IPv4 datagram (i.e., the octet
  that contains the IP version number (4) and Internet Header Length
  (IHL) ).  The IP datagram is encapsulated within the payload of an
  AAL-5 CPCS-PDU as specified in RFC 1483 and illustrated below:

















Newman, et. al.              Informational                      [Page 3]

RFC 1954               Flow Labelled IPv4 on ATM                May 1996


   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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  ~                         IPv4 Datagram                         ~
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                     Pad (0 - 47 octets)                       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  +                AAL-5 CPCS-PDU Trailer (8 octets)              +
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The MTU of an IPv4 datagram using Flow Type 0 encapsulation is 1500
  octets.

  Frames using Flow Type 0 encapsulation are sent to the VPI/VCI
  specified in the Label field of the corresponding IFMP Flow Type 0
  Redirect message element [IFMP].

4. Flow Type 1 Encapsulation

  All IPv4 frames using Flow Type 1 are encapsulated directly in the
  payload of an AAL-5 CPCS-PDU.  This is the null encapsulation of
  section 5.1 "VC based multiplexing of routed protocols" from RFC 1483
  [RFC1483].  There is no LLC/SNAP header.  Also, the following fields
  of the IP header are not transmitted: Version, Internet Header Length
  (IHL), Type of Service (TOS), Time to Live (TTL), Protocol, Source
  Address, and Destination Address.  In addition, the first 4 octets
  immediately following the IP header (as determined by the IHL field)
  are not transmitted.  (These 4 octets correspond to the source and
  destination ports for TCP and UDP datagrams.)  The value of the Total
  Length field is not changed; it remains the total length of the IP
  datagram before the above fields were removed.  The transmitted value
  of the Checksum field is the checksum value that would have been
  computed for the entire IP header if the TTL field had been set to
  zero (i.e., the actual value of the TTL field is "subtracted", using
  one's-complement arithmetic, from the Checksum before transmission).

  The IP datagram is encapsulated within the payload of an AAL-5 CPCS-
  PDU as specified in RFC 1483 and illustrated below:









Newman, et. al.              Informational                      [Page 4]

RFC 1954               Flow Labelled IPv4 on ATM                May 1996


   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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Total Length          |        Identification         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |Flags|     Fragment Offset     |           Checksum            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  ~                             Data                              ~
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                     Pad (0 - 47 octets)                       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  +                AAL-5 CPCS-PDU Trailer (8 octets)              +
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The MTU of the IPv4 datagram using Flow Type 1 encapsulation is 1484
  octets (1500 octets minus the 16 octets specified above).

  Frames using Flow Type 1 encapsulation are sent to the VPI/VCI
  specified in the Label field of the corresponding IFMP Flow Type 1
  redirect message element [IFMP].

5. Flow Type 2 Encapsulation

  All IPv4 frames using Flow Type 2 are encapsulated directly in the
  payload of an AAL-5 CPCS-PDU.  This is the null encapsulation of
  section 5.1 "VC based multiplexing of routed protocols" from RFC 1483
  [RFC1483].  There is no LLC/SNAP header.  Also, the following fields
  of the IP header are not transmitted: Version, Internet Header Length
  (IHL), Time to Live (TTL), Source Address, and Destination Address.
  The first 4 octets immediately following the IP header (as determined
  by the IHL field) are transmitted.  (These 4 octets correspond to the
  source and destination ports for TCP and UDP datagrams.) The value of
  the Total Length field is not changed; it remains the total length of
  the IP datagram before the above fields were removed.  The
  transmitted value of the Checksum field is the checksum value that
  would have been computed for the entire IP header if the TTL field
  had been set to zero (i.e., the actual value of the TTL field is
  "subtracted", using one's-complement arithmetic, from the Checksum
  before transmission).

  The IP datagram is encapsulated within the payload of an AAL-5 CPCS-
  PDU as specified in RFC 1483 and illustrated below:





Newman, et. al.              Informational                      [Page 5]

RFC 1954               Flow Labelled IPv4 on ATM                May 1996


   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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   Reserved    |Type of Service|         Total Length          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |        Identification         |Flags|     Fragment Offset     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   Reserved    |   Protocol    |           Checksum            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  ~                             Data                              ~
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                     Pad (0 - 47 octets)                       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  +                AAL-5 CPCS-PDU Trailer (8 octets)              +
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  The Reserved fields are not used and should be set to zero by the
  sender and ignored by the receiver.

  The MTU of the IPv4 datagram using Flow Type 2 encapsulation is 1492
  octets (1500 octets minus the 8 octets specified above).

  Frames using Flow Type 2 encapsulation are sent to the VPI/VCI
  specified in the Label field of the corresponding IFMP Flow Type 2
  redirect message element [IFMP].






















Newman, et. al.              Informational                      [Page 6]

RFC 1954               Flow Labelled IPv4 on ATM                May 1996


References

     [IFMP] Newman, P., et. al., "Ipsilon Flow Management Protocol
               Specification for IPv Version 1.0", Ipsilon Networks
               Inc., RFC 1953, May 1996.

     [RFC1483] Heinanen, J., "Multiprotocol Encapsulation over ATM
               Adaptation Layer 5", RFC 1483, July 1993.

SECURITY CONSIDERATIONS

  Security issues are not discussed in this document.

AUTHORS' ADDRESSES

  Peter Newman                        Phone: +1 (415) 846-4603
  Ipsilon Networks, Inc.              EMail: [email protected]

  W. L. Edwards, Chief Scientist      Phone:  +1 (913) 534 5334
  Sprint                              EMail:  [email protected]

  Robert M. Hinden                    Phone: +1 (415) 846-4604
  Ipsilon Networks, Inc.              EMail: [email protected]

  Eric Hoffman                        Phone: +1 (415) 846-4610
  Ipsilon Networks, Inc.              EMail: [email protected]

  Fong Ching Liaw                     Phone: +1 (415) 846-4607
  Ipsilon Networks, Inc.              EMail: [email protected]

  Tom Lyon                            Phone: +1 (415) 846-4601
  Ipsilon Networks, Inc.              EMail: [email protected]

  Greg Minshall                       Phone: +1 (415) 846-4605
  Ipsilon Networks, Inc.              EMail: [email protected]
















Newman, et. al.              Informational                      [Page 7]

RFC 1954               Flow Labelled IPv4 on ATM                May 1996


Ipsilon Networks, Inc. is located at:

  2191 East Bayshore Road
  Suite 100
  Palo Alto, CA 94303
  USA

Sprint is located at:

  Sprint
  Sprint Technology Services - Long Distance Division
  9300 Metcalf Avenue
  Mailstop KSOPKB0802
  Overland Park, KS 66212-6333
  USA




































Newman, et. al.              Informational                      [Page 8]


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