Network Working Group                                          A. Malis
Request for Comments: 4816                                      Verizon
Category: Standards Track                                    L. Martini
                                                         Cisco Systems
                                                            J. Brayley
                                                           ECI Telecom
                                                              T. Walsh
                                                      Juniper Networks
                                                         February 2007


              Pseudowire Emulation Edge-to-Edge (PWE3)
 Asynchronous Transfer Mode (ATM) Transparent Cell Transport Service

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 IETF Trust (2007).

Abstract

  The document describes a transparent cell transport service that
  makes use of the "N-to-one" cell relay mode for Pseudowire Emulation
  Edge-to-Edge (PWE3) Asynchronous Transfer-Mode (ATM) cell
  encapsulation.

1.  Introduction

  This transparent cell transport service allows migration of ATM
  services to a PSN without having to provision the ATM subscriber or
  customer edge (CE) devices.  The ATM CEs will view the ATM
  transparent cell transport service as if they were directly connected
  via a Time Division Multiplexer (TDM) leased line.  This service is
  most likely to be used as an internal function in an ATM service
  provider's network as a way to connect existing ATM switches via a
  higher-speed PSN, or to provide ATM "backhaul" services for remote
  access to existing ATM networks.







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RFC 4816      PWE3 ATM Transparent Cell Transport Service  February 2007


1.1.  Specification of Requirements

  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
  "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
  document are to be interpreted as described in RFC 2119 [1].

2.  Transparent Cell Transport Definition

  The transparent port service is a natural application of the "N-to-
  one" Virtual Circuit Connection (VCC) cell transport mode for PWE3
  ATM encapsulation described in [2], and MUST be used with pseudowires
  of type 0x0003, "ATM transparent cell transport" [4].

  The ATM transparent port service emulates connectivity between two
  remote ATM ports.  This service is useful when one desires to connect
  two CEs without processing or switching at the Virtual Path
  Connection (VPC) or VCC layer.  The ingress PE discards any
  idle/unassigned cells received from the ingress ATM port, and maps
  all other received cells to a single pseudowire.

  The egress PE does not change the Virtual Path Identifier (VPI),
  Virtual Circuit Identifier (VCI), Payload Type Identifier (PTI), or
  Cell Loss Priority (CLP) bits when it sends these cells on the egress
  ATM port.  Therefore, the transparent port service appears to emulate
  an ATM transmission convergence layer connection between two ports.
  However, since the ingress PE discards idle/unassigned cells, this
  service benefits from statistical multiplexing bandwidth savings.

  In accordance with [2], cell concatenation MAY be used for
  transparent cell-relay transport in order to save the PSN bandwidth.
  If used, it MUST be agreed between the ingress and egress PEs.  In
  particular, if the Pseudo Wire has been set up using the PWE3 control
  protocol [3], the ingress PE MUST NOT exceed the value of the
  "Maximum Number of concatenated ATM cells" Pseudowire Interface
  Parameter Sub-TLV (Interface Parameter ID = 0x02 [4]) received in the
  Label Mapping message for the Pseudo Wire, and MUST NOT use cell
  concatenation if this parameter has been omitted by the egress PE.

  ATM Operations and Management (OAM) cells MUST be transported
  transparently, and the PEs do not act on them.  If the PEs detect a
  PSN or pseudowire failure between them, they do not generate any OAM
  cells, but rather bring down the ATM interfaces to the CEs (e.g.,
  generating LOS on the ATM port), just as if it were a transmission
  layer failure.







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RFC 4816      PWE3 ATM Transparent Cell Transport Service  February 2007


  Similarly, ATM Integrated Local Management Interface (ILMI) signaling
  from the CEs, if any, MUST be transported transparently, and the PEs
  do not act on it.  However, the PEs must act on physical interface
  failure by either withdrawing the PW labels or by using pseudowire
  status signaling to indicate the interface failure.  The procedures
  for both alternatives are described in [3].

3.  Security Considerations

  This document does not introduce any new security considerations
  beyond those in [2] and [3].  This document defines an application
  that utilizes the encapsulation specified in [2], and does not
  specify the protocols used to carry the encapsulated packets across
  the PSN.  Each such protocol may have its own set of security issues,
  but those issues are not affected by the application specified
  herein.  Note that the security of the transported ATM service will
  only be as good as the security of the PSN.  This level of security
  might be less rigorous than a native ATM service.

4.  Congestion Control

  Since this document discusses an application of the "N-to-one" VCC
  cell transport mode for PWE3 ATM encapsulation described in [2], the
  congestion control considerations are identical to those discussed in
  section 15 of [2].  The PWE3 Working Group is also undertaking
  additional work on ATM-related congestion issues, and implementers
  should anticipate that an RFC will be published describing additional
  congestion control techniques that should be applied to ATM emulation
  over pseudowires.

5.  Normative References

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

  [2] Martini, L., Jayakumar, J., Bocci, M., El-Aawar, N., Brayley, J.,
      and G. Koleyni, "Encapsulation Methods for Transport of
      Asynchronous Transfer Mode (ATM) over MPLS Networks", RFC 4717,
      December 2006.

  [3] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G. Heron,
      "Pseudowire Setup and Maintenance Using the Label Distribution
      Protocol (LDP)", RFC 4447, April 2006.

  [4] Martini, L., "IANA Allocations for Pseudowire Edge to Edge
      Emulation (PWE3)", BCP 116, RFC 4446, April 2006.





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RFC 4816      PWE3 ATM Transparent Cell Transport Service  February 2007


Acknowledgments

  The authors would like to thank the members of the PWE3 working group
  for their assistance on this document, and Sasha Vainshtein of Axerra
  in particular for his comments and suggestions.

Author's Addresses

  Andrew G. Malis
  Verizon Communications
  40 Sylvan Road
  Waltham, MA

  EMail: [email protected]


  Luca Martini
  Cisco Systems, Inc.
  9155 East Nichols Avenue, Suite 400
  Englewood, CO, 80112

  EMail: [email protected]


  Jeremy Brayley
  ECI Telecom
  Omega Corporate Center
  1300 Omega Drive
  Pittsburgh, PA 15205

  EMail: [email protected]


  Tom Walsh
  Juniper Networks
  1194 N Mathilda Ave
  Sunnyvale, CA 94089

  EMail: [email protected]












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RFC 4816      PWE3 ATM Transparent Cell Transport Service  February 2007


Full Copyright Statement

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Acknowledgement

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  Internet Society.







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