On TCP-based Session Initiation Protocol (SIP) Server Overload Control

TL;DR

This paper investigates TCP-based SIP server overload control, revealing limitations of TCP flow control for overload management and proposing simple algorithms that significantly improve server throughput during overload conditions.

Contribution

It provides a comprehensive analysis of TCP-based SIP overload behavior and introduces novel overload control algorithms that enhance performance without protocol modifications.

Findings

TCP flow control alone is insufficient for SIP overload management

Proposed algorithms nearly restore full server capacity during overload

Insights applicable to other time-critical session-based applications

Abstract

The Session Initiation Protocol (SIP) server overload management has attracted interest since SIP is being widely deployed in the Next Generation Networks (NGN) as a core signaling protocol. Yet 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 leads to the important general 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.