Overload control in SIP servers: Evaluation and improvement

The Session Initiation Protocol (SIP) has gained momentum and is being widely used both in the Internet and Next Generation Telecommunications network as the core signaling protocol. SIP operation relies on SIP servers which are responsible for forwarding of SIP messages. It has been shown that the performance of SIP servers is largely degraded during overload conditions due to the built in message retransmission mechanism of SIP. This is an obstacle in wide deployment of SIP for a realistic situation. In this paper we propose a distributed and adaptive window based overload control algorithm, which controls the amount of calls that are forwarded to a downstream SIP server in an attempt to prevent it from being overloaded. Our scheme uses the call establishment delay as a measure of the amount of load on the downstream server and unlike other methods does not rely on explicit feedback. Using simulations we show that our proposed method performs better than a commonly used overload control algorithm and exhibits fast convergence and is stable.