10-04-2017, 09:29 PM
Abstract
SIP and SDP are used in 3G cellular IP Multimedia
Subsystems (IMS) to perform multimedia session setup and
maintenance. However, both protocols are text-based and
have large messages with sizes frequently exceeding
several hundred bytes. SigComp can be used to compress
these messages and greatly reduce the call setup and
feature invocation delays. In this paper, the potential gain
of using SigComp to compress SIP/SDP is demonstrated
through performance results. Our results show that
dictionary-based compression algorithms are best suited
for SigComp. Static and user-defined dictionaries are very
important for reducing the first several messages in a SIP
dialog while extended operations such as dynamic and
shared compression can significantly improve the overall
compression efficiency. On average, the message sizes can
be reduced by as much as 88% with negligible
compression/decompression time.
1. Introduction
Session Initiation Protocol (SIP) [1] is a signaling
protocol developed by IETF for session control in
applications such as Internet conferencing, voice over IP,
presence, and instant messaging. Session Description
Protocol (SDP) [2] is a protocol intended for describing
multimedia sessions for the purposes of session
announcement, session invitation and other forms of
multimedia session initiation. SIP and SDP are often used
in combination to initiate and manage multimedia
communication sessions.
With the convergence of cellular systems to an All-IP
architecture, SIP has been chosen as the signaling protocol
for multimedia session control. For example, the IMS in
both 3GPP and 3GPP2 use SIP as the signaling protocol for
session establishment and maintenance. However, both SIP
and SDP are text-based protocols and they are 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 [3].
When used over wireless links such as those in 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 large number of messages that are
required in some flows, call setup and feature invocation
usually experience very large delays. SigComp [6]
provides a method to eliminate this problem by offering
robust, lossless compression of application messages. The
Universal Decompression Virtual Machine (UDVM) in
SigComp provides decompression functionalities for a wide
variety of compression algorithms.
In this paper, we study the performance of SigComp
when it is used to compress SIP/SDP session setup
messages. Results for both compression efficiencies and
memory usage are presented for a basic LZ77 algorithm and
the Deflate [4] algorithm. It is shown that, on average, the
SIP messages during a call setup can be compressed to
around 12% of the original size. We also present results to
show the effect of different state information on
compression efficiency. Static dictionary, user-defined
dictionary and extended operations are all effective ways to
significantly improve compression efficiency.
The paper is organized as follows. In Section 2, we
briefly describe the SigComp concept as well as how
dictionaries and extended operations can be used to
improve compression efficiency; in Section 3, we give an
overview of the current available text compression
algorithms and discuss whether they are suitable for
SigComp; the performance results are presented and
compared in Section 4. We conclude the paper with Section
5.
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