Improving performance of SIP signaling during overload using capabilities of connection-oriented transport protocol

Over the past decade, voice communications have moved from the public switched telephone networks to the Internet. The IETF has enabled this transition by developing stable standards for call setup and media transport. Session Initiation Protocol (SIP) is an application-layer protocol for creating, modifying, and terminating media sessions in the internet. SIP is becoming the core signaling protocol for Next Generation Networks. Since the built-in rejection mechanism of SIP is incapable of handling SIP overload in servers, SIP server overload management has attracted interest recently. Despite the fact that TCP is increasingly seen as the more suitable choice for SIP transport, most of the existing SIP overload control works have focused on SIP-over-UDP. Furthermore, most of researchers have focused on solving the overload problem in core servers, and therefore overload in edge servers still exists. We propose and implement novel but simple overload control mechanism which rejects a TCP connection at transport protocol level. Our work demonstrates that TCP in handshaking phase alone, is capable of managing the overload of time-critical session-based applications, which reject call requests in transport layer, with virtually no overhead. Experimental evaluation shows that with our mechanism, server capacity during overload improves from its original zero throughput in edge servers to nearly full capacity.