A Study on SIP Session Timer for Wireless VoIP
Date Issued
2004
Date
2004
Author(s)
Liu, Chih-Hsiao
DOI
en-US
Abstract
Supporting telephony services over Internet Protocol (IP) network or the so called voice over
IP (VoIP) is considered as a promising trend in telecommunication business. Session Initiation
Protocol (SIP) speci£ed in the Internet Engineering Task Force (IETF) is the most promising candidate
for call setup signaling for future VoIP services. With versatile applications provided, SIP
is becoming a real competitor to plain old telephone service.
However, the basic SIP de£ned in IETF RFC 3261 does not de£ne a mechanism for proxy
servers to track the states of the communicating sessions. In other words, a SIP proxy server is
not able to determine whether an established session is still active or dead. A SIP proxy may hold
some unused resources (e.g., allocated memory) revsered for a dead session, which may result
in the blockings of other new session requests due to the lack of the resources. To resolve this
problem, the SIP Extension de£nes a keep-alive (i.e., refresh) mechanism, SIP Session Timer, for
monitoring the state of SIP sessions.
Based on SIP Session Timer, we propose a dynamic refresh method to dynamically adjust the
session timer depending on the network situation. With our dynamic refresh method, the session
failure can be ef£ciently detected. An analytic and a simulation models are proposed to investigate
the performance of the static refresh and our proposed dynamic refresh methods. The numerical
results indicate that in terms of average refresh number, average bad debt, and the mis-detection
probability, our dynamic refresh method signi£cantly outperforms the static one.
Subjects
連線計時器
連線初始化通訊協定
語音服務
網際網路
SIP Session Timer
voice over IP
Session Initial Protocol
Type
thesis
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