RObust Header Compression (ROHC): A Link-Layer Assisted Profile for IP/UDP/RTP
RFC 3242

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• 03

Network Working Group                                       L-E. Jonsson
Request for Comments: 3242                                  G. Pelletier
Category: Standards Track                                       Ericsson
                                                              April 2002

                   RObust Header Compression (ROHC):
              A Link-Layer Assisted Profile for IP/UDP/RTP

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 (2002).  All Rights Reserved.

Abstract

   This document defines a ROHC (Robust Header Compression) profile for
   compression of IP/UDP/RTP (Internet Protocol/User Datagram
   Protocol/Real-Time Transport Protocol) packets, utilizing
   functionality provided by the lower layers to increase compression
   efficiency by completely eliminating the header for most packets
   during optimal operation.  The profile is built as an extension to
   the ROHC RTP profile.  It defines additional mechanisms needed in
   ROHC, states requirements on the assisting layer to guarantee
   transparency, and specifies general logic for compression and
   decompression making use of this header-free packet.

Table of Contents

   1.  Introduction....................................................2
   2.  Terminology.....................................................4
   3.  Overview of the Link-Layer Assisted Profile.....................5
        3.1.  Providing Packet Type Identification.....................6
        3.2.  Replacing the Sequence Number............................6
        3.3.  CRC Replacement..........................................7
        3.4.  Applicability of This Profile............................7
   4.  Additions and Exceptions Compared to ROHC RTP...................8
        4.1.  Additional Packet Types..................................8
               4.1.1.  No-Header Packet (NHP)..........................8
               4.1.2.  Context Synchronization Packet (CSP)............8
               4.1.3.  Context Check Packet (CCP)......................9

Jonsson, et. al             Standards Track                     [Page 1]
RFC 3242             A Link-Layer Assisted ROHC RTP           April 2002

        4.2.  Interfaces Towards the Assisting Layer..................11
               4.2.1.  Interface, Compressor to Assisting Layer.......11
               4.2.2.  Interface, Assisting Layer to Decompressor.....12
        4.3.  Optimistic Approach Agreement...........................13
        4.4.  Fast Context Initialization, IR Redefinition............13
        4.5.  Feedback Option, CV-REQUEST.............................14
        4.6.  Periodic Context Verification...........................15
        4.7.  Use of Context Identifier...............................15
   5.  Implementation Issues..........................................15
        5.1.  Implementation Parameters and Signals...................15
               5.1.1.  Implementation Parameters at the Compressor....16
               5.1.2.  Implementation Parameters at the Decompressor..17
        5.2.  Implementation over Various Link Technologies...........18
   6.  IANA Considerations............................................18
   7.  Security Considerations........................................18
   8.  Acknowledgements...............................................18
   9.  References.....................................................19
   10. Authors' Addresses.............................................20
   11. Full Copyright Statement.......................................21

1.  Introduction

   Header compression is a technique used to compress and transparently
   decompress the header information of a packet on a per-hop basis,
   utilizing redundancy within individual packets and between
   consecutive packets within a packet stream.  Over the years, several
   protocols [VJHC, IPHC] have been developed to compress the network
   and transport protocol headers [IPv4, IPv6, UDP, TCP], and these
   schemes have been successful in improving efficiency over many wired
   bottleneck links, such as modem connections over telephone networks.
   In addition to IP, UDP, and TCP compression, an additional
   compression scheme called Compressed RTP [CRTP] has been developed to
   further improve compression efficiency for the case of real-time
   traffic using the Real-Time Transport Protocol [RTP].

   The schemes mentioned above have all been designed taking into
   account normal assumptions about link characteristics, which
   traditionally have been based on wired links only.  However, with an