Signaling Compression (SigComp) Users' Guide
RFC 4464

Document Type RFC - Informational (May 2006; No errata)
Last updated 2013-03-02
Stream IETF
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Stream WG state (None)
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IESG IESG state RFC 4464 (Informational)
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Responsible AD Magnus Westerlund
Send notices to cabo@tzi.org, lars-erik.jonsson@ericsson.com
Network Working Group                                         A. Surtees
Request for Comments: 4464                                       M. West
Category: Informational                      Siemens/Roke Manor Research
                                                                May 2006

              Signaling Compression (SigComp) Users' Guide

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document provides an informational guide for users of the
   Signaling Compression (SigComp) protocol.  The aim of the document is
   to assist users when making SigComp implementation decisions, for
   example, the choice of compression algorithm and the level of
   robustness against lost or misordered packets.

Surtees & West               Informational                      [Page 1]
RFC 4464                  SigComp Users' Guide                  May 2006

Table of Contents

   1. Introduction ....................................................3
   2. Overview of the User Guide ......................................3
   3. UDVM Assembly Language ..........................................4
      3.1. Lexical Level ..............................................4
      3.2. Syntactic Level ............................................5
           3.2.1. Expressions .........................................7
           3.2.2. Instructions ........................................8
           3.2.3. Directives ..........................................9
           3.2.4. Labels .............................................10
      3.3. Uploading the Bytecode to the UDVM ........................11
   4. Compression Algorithms .........................................12
      4.1. Well-known Compression Algorithms .........................12
           4.1.1. LZ77 ...............................................12
           4.1.2. LZSS ...............................................16
           4.1.3. LZW ................................................18
           4.1.4. DEFLATE ............................................21
           4.1.5. LZJH ...............................................24
      4.2. Adapted Algorithms ........................................28
           4.2.1. Modified DEFLATE ...................................28
   5. Additional SigComp Mechanisms ..................................31
      5.1. Acknowledging a State Item ................................32
      5.2. Static Dictionary .........................................33
      5.3. CRC Checksum ..............................................34
      5.4. Announcing Additional Resources ...........................35
      5.5. Shared Compression ........................................37
   6. Security Considerations ........................................38
   7. Acknowledgements ...............................................38
   8. Intellectual Property Right Considerations .....................38
   9. Informative References .........................................38
   Appendix A. UDVM Bytecode for the Compression Algorithms ..........40
      A.1. Well-known Algorithms .....................................40
           A.1.1.  LZ77 ..............................................40
           A.1.2.  LZSS ..............................................40
           A.1.3.  LZW ...............................................40
           A.1.4.  DEFLATE ...........................................40
           A.1.5.  LZJH ..............................................41
      A.2. Adapted Algorithms ........................................41
           A.2.1. Modified DEFLATE ...................................41

Surtees & West               Informational                      [Page 2]
RFC 4464                  SigComp Users' Guide                  May 2006

1.  Introduction

   This document provides an informational guide for users of the
   SigComp protocol, RFC 3320 [2].  The idea behind SigComp is to
   standardize a Universal Decompressor Virtual Machine (UDVM) that can
   be programmed to understand the output of many well-known compressors
   including DEFLATE [8] and LZW [7].  The bytecode for the chosen
   compression algorithm is uploaded to the UDVM as part of the
   compressed data.

   The basic SigComp RFC describes the actions that an endpoint must
   take upon receiving a SigComp message.  However, the entity
   responsible for generating new SigComp messages (the SigComp
   compressor) is left as an implementation decision; any compressor can
   be used provided that it generates SigComp messages that can be
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