The Session Initiation Protocol (SIP) and Session Description Protocol (SDP) Static Dictionary for Signaling Compression (SigComp)
RFC 3485

Document Type RFC - Proposed Standard (March 2003; No errata)
Updated by RFC 4896
Last updated 2015-10-14
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IESG IESG state RFC 3485 (Proposed Standard)
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Network Working Group                                   M. Garcia-Martin
Request for Comments: 3485                                      Ericsson
Category: Standards Track                                     C. Bormann
                                                                  J. Ott
                                                          TZI/Uni Bremen
                                                                R. Price
                                                      Siemens/Roke Manor
                                                             A. B. Roach
                                                             dynamicsoft
                                                           February 2003

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

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 (2003).  All Rights Reserved.

Abstract

   The Session Initiation Protocol (SIP) is a text-based protocol for
   initiating and managing communication sessions.  The protocol can be
   compressed by using Signaling Compression (SigComp).  Similarly, the
   Session Description Protocol (SDP) is a text-based protocol intended
   for describing multimedia sessions for the purposes of session
   announcement, session invitation, and other forms of multimedia
   session initiation.  This memo defines the SIP/SDP-specific static
   dictionary that SigComp may use in order to achieve higher
   efficiency.  The dictionary is compression algorithm independent.

Garcia-Martin, et al.       Standards Track                     [Page 1]
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                     [Page 2]
RFC 3485       SIP and SDP Static Dictionary for SigComp   February 2003

2. Design considerations

   The static SIP/SDP dictionary is a collection of well-known strings
   that appear in most of the SIP and SDP messages.  The dictionary is
   not a comprehensive list of reserved words, but it includes many of
   the strings that appear in SIP and SDP signaling.
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