SERvartuka: Dynamic distribution of state to improve SIP server scalability

Abstract

A growing class of applications, including VoIP, IM and Presence, are enabled by the Session Initiation Protocol (SIP). Requests in SIP typically traverse through multiple proxies. The availability of multiple proxies offers the flexibility to distribute proxy functionality across several nodes. In particular, after experimentally demonstrating that the resource consumption of maintaining state is significant, we define the problem of state distribution across multiple nodes when the goal is to increase overall call throughput. We first formulate this as an optimization problem and then derive a distributed algorithm from it. This distributed algorithm leads to the design and evaluation of SERvartuka, a more scalable SIP server that dynamically determines the number of SIP requests for which the server is stateful while delegating state maintenance for the remainder of the requests to a server further downstream. This design is in contrast to existing SIP servers that are statically configured to either be stateless or stateful and therefore result in sub-optimal call throughput. We implement SERvartuka on top of OpenSER, a commercial SIP proxy server and measure performance benefits of different server configurations. An example of our results is a 20% percent increase in call throughput when using our algorithm for a configuration of two servers in series. © 2008 IEEE.