2009 Reports

On TCP-based SIP Server Overload Control

Shen, Charles; Schulzrinne, Henning G.

SIP server overload management has attracted interest recently as SIP becomes the core signaling protocol for Next Generation Networks. Yet virtually all existing SIP overload control work is focused on SIP-over-UDP, despite the fact that TCP is increasingly seen as the more viable choice of SIP transport. This paper answers the following questions: is the existing TCP flow control capable of handling the SIP overload problem? If not, why and how can we make it work? We provide a comprehensive explanation of the default SIP-over-TCP overload behavior through server instrumentation. We also propose and implement novel but simple overload control algorithms without any kernel or protocol level modification. Experimental evaluation shows that with our mechanism the overload performance improves from its original zero throughput to nearly full capacity. Our work also leads to the important high level insight that the traditional notion of TCP flow control alone is incapable of managing overload for time-critical session based applications, which would be applicable not only to SIP, but also to a wide range of other common applications such as database servers.