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Applying Signaling Compression (SigComp) to the Session Initiation Protocol (SIP)
RFC 5049

Network Working Group                                         C. Bormann
Request for Comments: 5049                       Universitaet Bremen TZI
Category: Standards Track                                         Z. Liu
                                                   Nokia Research Center
                                                                R. Price
                               EADS Defence and Security Systems Limited
                                                       G. Camarillo, Ed.
                                                                Ericsson
                                                           December 2007

                Applying Signaling Compression (SigComp)
                to the Session Initiation Protocol (SIP)

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.

Abstract

   This document describes some specifics that apply when Signaling
   Compression (SigComp) is applied to the Session Initiation Protocol
   (SIP), such as default minimum values of SigComp parameters,
   compartment and state management, and a few issues on SigComp over
   TCP.  Any implementation of SigComp for use with SIP must conform to
   this document and SigComp, and in addition, support the SIP and
   Session Description Protocol (SDP) static dictionary.

Bormann, et al.             Standards Track                     [Page 1]
RFC 5049                Applying SigComp to SIP            December 2007

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................3
   3. Compliance with This Specification ..............................3
   4. Minimum Values of SigComp Parameters for SIP/SigComp ............3
      4.1. decompression_memory_size (DMS) for SIP/SigComp ............4
      4.2. state_memory_size (SMS) for SIP/SigComp ....................4
      4.3. cycles_per_bit (CPB) for SIP/SigComp .......................5
      4.4. SigComp_version (SV) for SIP/SigComp .......................5
      4.5. locally available state (LAS) for SIP/SigComp ..............5
   5. Delimiting SIP Messages and SigComp Messages on the Same Port ...5
   6. Continuous Mode over TCP ........................................6
   7. Too-Large SIP Messages ..........................................7
   8. SIP Retransmissions .............................................7
   9. Compartment and State Management for SIP/SigComp ................7
      9.1. Remote Application Identification ..........................8
      9.2. Identifier Comparison Rules ...............................10
      9.3. Compartment Opening and Closure ...........................11
      9.4. Lack of a Compartment .....................................13
   10. Recommendations for Network Administrators ....................13
   11. Private Agreements ............................................14
   12. Backwards Compatibility .......................................14
   13. Interactions with Transport Layer Security (TLS) ..............14
   14. Example .......................................................15
   15. Security Considerations .......................................17
   16. IANA Considerations ...........................................17
   17. Acknowledgements ..............................................17
   18. References ....................................................18
      18.1. Normative References .....................................18
      18.2. Informative References ...................................19

Bormann, et al.             Standards Track                     [Page 2]
RFC 5049                Applying SigComp to SIP            December 2007

1.  Introduction

   SigComp [RFC3320] is a solution for compressing messages generated by
   application protocols.  Although its primary driver is to compress
   SIP [RFC3261] messages, the solution itself has been intentionally
   designed to be application agnostic so that it can be applied to any
   application protocol; this is denoted as ANY/SigComp.  Consequently,
   many application-dependent specifics are left out of the base
   standard.  It is intended that a separate specification be used to
   describe those specifics when SigComp is applied to a particular
   application protocol.

   This document binds SigComp and SIP; this is denoted as SIP/SigComp.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",

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