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Signaling Compression (SigComp)
RFC 3320

Network Working Group                                           R. Price
Request for Comments: 3320                            Siemens/Roke Manor
Category: Standards Track                                     C. Bormann
                                                          TZI/Uni Bremen
                                                      J. Christoffersson
                                                                H. Hannu
                                                                Ericsson
                                                                  Z. Liu
                                                                   Nokia
                                                            J. Rosenberg
                                                             dynamicsoft
                                                            January 2003

                    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

   This document defines Signaling Compression (SigComp), a solution for
   compressing messages generated by application protocols such as the
   Session Initiation Protocol (SIP) (RFC 3261) and the Real Time
   Streaming Protocol (RTSP) (RFC 2326).  The architecture and
   prerequisites of SigComp are outlined, along with the format of the
   SigComp message.

   Decompression functionality for SigComp is provided by a Universal
   Decompressor Virtual Machine (UDVM) optimized for the task of running
   decompression algorithms.  The UDVM can be configured to understand
   the output of many well-known compressors such as DEFLATE (RFC-1951).

Price, et. al.              Standards Track                     [Page 1]
RFC 3320            Signaling Compression (SigComp)         January 2003

Table of Contents

   1.  Introduction...................................................2
   2.  Terminology....................................................3
   3.  SigComp architecture...........................................5
   4.  SigComp dispatchers...........................................15
   5.  SigComp compressor............................................18
   6.  SigComp state handler.........................................20
   7.  SigComp message format........................................23
   8.  Overview of the UDVM..........................................28
   9.  UDVM instruction set..........................................37
   10. Security Considerations.......................................56
   11. IANA Considerations...........................................58
   12. Acknowledgements..............................................59
   13. References....................................................59
   14. Authors' Addresses............................................60
   15. Full Copyright Statement......................................62

1.  Introduction

   Many application protocols used for multimedia communications are
   text-based and engineered for bandwidth rich links.  As a result the
   messages have not been optimized in terms of size.  For example,
   typical SIP messages range from a few hundred bytes up to two
   thousand bytes or more [RFC3261].

   With the planned usage of these protocols in wireless handsets as
   part of 2.5G and 3G cellular networks, the large message size is
   problematic.  With low-rate IP connectivity the transmission delays
   are significant.  Taking into account retransmissions, and the
   multiplicity of messages that are required in some flows, call setup
   and feature invocation are adversely affected.  SigComp provides a
   means to eliminate this problem by offering robust, lossless
   compression of application messages.

   This document outlines the architecture and prerequisites of the
   SigComp solution, the format of the SigComp message and the Universal
   Decompressor Virtual Machine (UDVM) that provides decompression
   functionality.

   SigComp is offered to applications as a layer between the application
   and an underlying transport.  The service provided is that of the
   underlying transport plus compression.  SigComp supports a wide range
   of transports including TCP, UDP and SCTP [RFC-2960].

Price, et. al.              Standards Track                     [Page 2]
RFC 3320            Signaling Compression (SigComp)         January 2003

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