RFC 3485 (rfc3485) - Page 2 of 30

The Session Initiation Protocol (SIP) and Session Description Protocol (SDP) Static Dictionary for Signaling Compression (SigComp)

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RFC 3485       SIP and SDP Static Dictionary for SigComp   February 2003


Table of Contents

   1. Introduction.....................................................2
   2. Design considerations............................................3
   3. Binary representation of the SIP/SDP dictionary..................5
   4. Security Considerations.........................................13
   5. IANA Considerations.............................................13
   6. Acknowledgements................................................14
   7. References......................................................14
      7.1 Normative References........................................14
      7.2 Informative References......................................14
   Appendix A. SIP input strings to the SIP/SDP static dictionary.....17
   Appendix B. SDP input strings to the SIP/SDP static dictionary.....26
   Authors' Addresses.................................................29
   Full Copyright Statement...........................................30

1. Introduction

   SIP [3] and SDP [24] are text-based protocols that use the UTF-8
   charset (RFC 2279 [5]).  SIP and SDP were designed for rich bandwidth
   links.  However, when SIP/SDP is run over narrow bandwidth links,
   such as radio interfaces or low speed serial links, the session setup
   time increases substantially, compared to an operation over a rich
   bandwidth link.

   The session setup time can decrease dramatically if the SIP/SDP
   signaling is compressed.  The signaling compression mechanisms
   specified in SigComp [1] provide a multiple compression/decompression
   algorithm framework to compress and decompress text-based protocols
   such as SIP and SDP.

   When compression is used in SIP/SDP, the compression achieves its
   maximum rate once a few message exchanges have taken place.  This is
   due to the fact that the first message the compressor sends to the
   decompressor is only partially compressed, as there is not a previous
   stored state to compress against.  As the goal is to reduce the
   session setup time as much as possible, it seems sensible to
   investigate a mechanism to boost the compression rate from the first
   message.

   In this memo we introduce the static dictionary for SIP and SDP.  The
   dictionary is to be used in conjunction with SIP, SDP and SigComp.
   The static SIP/SDP dictionary constitutes a SigComp state that can be
   referenced in the first SIP message that the compressor sends out.







Garcia-Martin, et al.       Standards Track
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