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