Encapsulation Methods for Transport of Frame Relay over Multiprotocol Label Switching (MPLS) Networks
RFC 4619

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Network Working Group                                    L. Martini, Ed.
Request for Comments: 4619                           Cisco Systems, Inc.
Category: Standards Track                                   C. Kawa, Ed.
                                                       Oz Communications
                                                           A. Malis, Ed.
                                                                 Tellabs
                                                          September 2006

        Encapsulation Methods for Transport of Frame Relay over
             Multiprotocol Label Switching (MPLS) Networks

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 (2006).

Abstract

   A frame relay pseudowire is a mechanism that exists between a
   provider's edge network nodes and that supports as faithfully as
   possible frame relay services over an MPLS packet switched network
   (PSN).  This document describes the detailed encapsulation necessary
   to transport frame relay packets over an MPLS network.

Martini & Kawa              Standards Track                     [Page 1]
RFC 4619       Encapsulation for Transport of Frame Relay September 2006

Table of Contents

   1. Introduction ....................................................2
   2. Specification of Requirements ...................................4
   3. Co-authors ......................................................4
   4. Acronyms and Abbreviations ......................................5
   5. Applicability Statement .........................................5
   6. General Encapsulation Method ....................................6
   7. Frame Relay over MPLS PSN for the One-to-One Mode ...............7
      7.1. MPLS PSN Tunnel and PW .....................................7
      7.2. Packet Format over MPLS PSN ................................7
      7.3. The Control Word ...........................................8
      7.4. The Martini Legacy Mode Control Word .......................9
      7.5. PW Packet Processing .......................................9
           7.5.1. Encapsulation of Frame Relay Frames .................9
           7.5.2. Setting the Sequence Number ........................10
      7.6. Decapsulation of PW Packets ...............................11
           7.6.1. Processing the Sequence Number .....................11
           7.6.2. Processing of the Length Field by the Receiver .....11
      7.7. MPLS Shim EXP Bit Values ..................................12
      7.8. MPLS Shim S Bit Value .....................................12
      7.9. Control Plane Details for Frame Relay Service .............12
           7.9.1. Frame Relay Specific Interface Parameter Sub-TLV ...12
   8. Frame Relay Port Mode ..........................................13
   9. Congestion Control .............................................13
   10. Security Considerations .......................................14
   11. Normative References ..........................................14
   12. Informative References ........................................15

1.   Introduction

   In an MPLS or IP network, it is possible to use control protocols
   such as those specified in [RFC4447] to set up "pseudowires" (PWs)
   that carry the Protocol Data Units of layer 2 protocols across the
   network.  A number of these emulated PWs may be carried in a single
   tunnel.  The main functions required to support frame relay PW by a
   Provider Edge (PE) include:

   - encapsulation of frame relay specific information in a suitable
     pseudowire (PW) packet;

   - transfer of a PW packet across an MPLS network for delivery to a
     peer PE;

   - extraction of frame relay specific information from a PW packet by
     the remote peer PE;

Martini & Kawa              Standards Track                     [Page 2]
RFC 4619       Encapsulation for Transport of Frame Relay September 2006

   - regeneration of native frame relay frames for forwarding across an
     egress port of the remote peer PE; and

   - execution of any other operations as required to support frame
     relay service.

   This document specifies the encapsulation for the emulated frame
   relay VC over an MPLS PSN.  Although different layer 2 protocols
   require different information to be carried in this encapsulation, an
   attempt has been made to make the encapsulation as common as possible
   for all layer 2 protocols.  Other layer 2 protocols are described in
   separate documents.  [ATM] [RFC4448] [RFC4618]

   The following figure describes the reference models that are derived