A Study on SIP Session Timer for Wireless VoIP

• Main Authors: Chih-Hsiao Liu, 劉志孝
• Other Authors: Ai-Chun Pang
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/63222228284321030288

碩士 === 國立臺灣大學 === 資訊工程學研究所 === 92 === 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.