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Stability Analysis of Tandem SIP Proxies

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Executive Summary

It has been shown that the throughput of Session Initiation Protocol (SIP) proxies is largely degraded during overload conditions due to the built in message retransmission mechanism of SIP. Many overload control algorithms have been proposed with the objective of keeping SIP proxy throughput at an acceptable level when overload occurs. In this paper, the authors view the overload problem as a Lyapunov stability problem. They consider the standard SIP trapezoid topology consisting of an upstream and downstream proxy operating in tandem. They provide a fluid flow model for the operation of this system under overload. They write state space equations for the tandem proxy system and using Lyapunov stability criterion derive stability conditions for it.

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