Signaling Compression (SigComp) Requirements & Assumptions
RFC 3322

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Network Working Group                                           H. Hannu
Request for Comments: 3322                                      Ericsson
Category: Informational                                     January 2003

       Signaling Compression (SigComp) Requirements & Assumptions

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 (2003).  All Rights Reserved.

Abstract

   The purpose of this document is to outline requirements and
   motivations for the development of a scheme for compression and
   decompression of messages from signaling protocols.  In wireless
   environments and especially in cellular systems, e.g., GSM (Global
   System for Mobile communications) and UMTS (Universal Mobile
   Telecommunications System), there is a need to maximize the transport
   efficiency for data over the radio interface.  With the introduction
   of SIP/SDP (Session Initiation Protocol/Session Description Protocol)
   to cellular devices, compression of the signaling messages should be
   considered in order to improve both service availability and quality,
   mainly by reducing the user idle time, e.g., at call setup.

Table of Contents

   1.  Introduction....................................................2
   1.1.  Protocol Characteristics......................................2
   1.2.  Cellular System Radio Characteristics.........................3
   2.  Motivation for Signaling Reduction..............................4
   2.1.  Estimation of Call Setup Delay Using SIP/SDP..................4
   3.  Alternatives for Signaling Reduction............................6
   4.  Assumptions.....................................................7
   5.  Requirements....................................................8
   5.1.  General Requirements..........................................8
   5.2.  Performance Requirements......................................9
   6. Security Considerations.........................................11
   7. IANA Considerations.............................................11
   8. References......................................................11
   9. Author's Address................................................12
   10. Full Copyright Statement.......................................13

Hannu                        Informational                      [Page 1]
RFC 3322           SigComp Requirements & Assumptions       January 2003

1. Introduction

   In wireless environments, and especially in cellular systems, such as
   GSM/GPRS, there is a need to maximize the transport efficiency of
   data over the radio interface.  The radio spectrum is rather
   expensive and must be carefully used.  Therefore, the cellular
   systems must support a sufficient number of users to make them
   economically feasible.  Thus, there is a limitation in the per user
   bandwidth.

   Compressing the headers of the network and transport protocols used
   for carrying user data is one way to make more efficient use of the
   scarce radio resources [ROHC].  However, compression of the messages
   from signaling protocols, such as SIP/SDP, should also be considered
   to increase the radio resource usage even further.  Compression will
   also improve the service quality by reducing the user idle time at
   e.g., call setup.  When IP is used end-to-end, new applications, such
   as streaming, will be brought to tiny end-hosts, such as cellular
   devices.  This will introduce additional traffic in cellular systems.
   Compression of signaling messages, such as RTSP [RTSP], should also
   be considered to improve both the service availability and quality.

   New services with their corresponding signaling protocols make it
   reasonable to consider a scheme that is generic.  The scheme should
   be generic in the meaning that the scheme can efficiently be applied
   to arbitrary protocols with certain characteristics, such as the
   ASCII based protocols SIP and RTSP.

1.1. Protocol Characteristics

   The following application signaling protocols are examples of
   protocols that are expected to be commonly used in the future.  Some
   of their characteristics are described below.

1.1.1 SIP

   The Session Initiation Protocol [SIP] is an application layer
   protocol for establishing, modifying and terminating multimedia
   sessions or calls.  These sessions include Internet multimedia
   conferences, Internet telephony and similar applications.  SIP can be
   used over either TCP [TCP] or UDP [UDP].  SIP is a text based
   protocol, using ISO 10646 in UTF-8 encoding.

Hannu                        Informational                      [Page 2]
RFC 3322           SigComp Requirements & Assumptions       January 2003

1.1.2 SDP

   The Session Description Protocol [SDP] is used to advertise
   multimedia conferences and communicate conference addresses and