Pseudowire Emulation Edge-to-Edge (PWE3) Asynchronous Transfer Mode (ATM) Transparent Cell Transport Service
RFC 4816

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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.

Malis, et al.               Standards Track                     [Page 1]
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.

Malis, et al.               Standards Track                     [Page 2]
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