RFC 3242 (rfc3242) - Page 2 of 21

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

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
   increasing number of wireless links in the Internet paths, these
   assumptions are no longer generally valid.  In wireless environments,
   especially wide coverage cellular environments, relatively high error
   rates are tolerated in order to allow efficient usage of the radio
   resources.  For real-time traffic, which is more sensitive to delays
   than to errors, such operating conditions will be norm over, for
   example, 3rd generation cellular links, and header compression must
   therefore tolerate packet loss.  However, with the previously
   mentioned schemes, especially for real-time traffic compressed by
   CRTP, high error rates have been shown to significantly degrade



Jonsson, et. al             Standards Track