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Protocol Extensions for Header Compression over MPLS
RFC 4901

Network Working Group                                        J. Ash, Ed.
Request for Comments: 4901                                  J. Hand, Ed.
Category: Standards Track                                           AT&T
                                                           A. Malis, Ed.
                                                  Verizon Communications
                                                               June 2007

          Protocol Extensions for Header Compression over MPLS

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

   This specification defines how to use Multi-Protocol Label Switching
   (MPLS) to route Header-Compressed (HC) packets over an MPLS label
   switched path.  HC can significantly reduce packet-header overhead
   and, in combination with MPLS, can also increases bandwidth
   efficiency and processing scalability in terms of the maximum number
   of simultaneous compressed flows that use HC at each router).  Here
   we define how MPLS pseudowires are used to transport the HC context
   and control messages between the ingress and egress MPLS label
   switching routers.  This is defined for a specific set of existing HC
   mechanisms that might be used, for example, to support voice over IP.
   This specification also describes extension mechanisms to allow
   support for future, as yet to be defined, HC protocols.  In this
   specification, each HC protocol operates independently over a single
   pseudowire instance, very much as it would over a single point-to-
   point link.

Ash, et al.                 Standards Track                     [Page 1]
RFC 4901         Header Compression over MPLS Protocol         June 2007

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................3
   3. Header Compression over MPLS Protocol Overview ..................6
   4. Protocol Specifications ........................................11
      4.1. MPLS Pseudowire Setup and Signaling .......................13
      4.2. Header Compression Scheme Setup, Negotiation, and
           Signaling .................................................14
           4.2.1. Configuration Option Format [RFC3544] ..............15
           4.2.2. RTP-Compression Suboption [RFC3544] ................17
           4.2.3. Enhanced RTP-Compression Suboption [RFC3544] .......18
           4.2.4. Negotiating Header Compression for Only TCP
                  or Only Non-TCP Packets [RFC3544] ..................19
           4.2.5. Configuration Option Format [RFC3241] ..............20
           4.2.6. PROFILES Suboption [RFC3241] .......................21
      4.3. Encapsulation of Header Compressed Packets ................22
      4.4. Packet Reordering .........................................23
   5. HC Pseudowire Setup Example ....................................24
   6. Security Considerations ........................................29
   7. Acknowledgements ...............................................29
   8. IANA Considerations ............................................29
   9. Normative References ...........................................30
   10. Informative References ........................................31
   11. Contributors ..................................................33

Ash, et al.                 Standards Track                     [Page 2]
RFC 4901         Header Compression over MPLS Protocol         June 2007

1.  Introduction

   Voice over IP (VoIP) typically uses the encapsulation
   voice/RTP/UDP/IP.  When MPLS labels [RFC3031] are added, this becomes
   voice/RTP/UDP/IP/MPLS-labels.  MPLS VPNs (e.g., [RFC4364]) use label
   stacking, and in the simplest case of IPv4 the total packet header is
   at least 48 bytes, while the voice payload is often no more than 30
   bytes, for example.  When IPv6 is used, the relative size of the
   header in comparison to the payload is even greater.  The interest in
   header compression (HC) is to exploit the possibility of
   significantly reducing the overhead through various compression
   mechanisms, such as with enhanced compressed RTP (ECRTP) [RFC3545]
   and robust header compression (ROHC) [RFC3095, RFC3095bis, RFC4815],
   and also to increase scalability of HC.  MPLS is used to route HC
   packets over an MPLS label switched path (LSP) without

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