Load Balancing Algorithms for the Session Initiation Protocol

This paper introduces several novel load balancing algorithms for distributing Session Initiation Protocol (SIP) requests to a cluster of SIP servers. Our load balancer improves both throughput and response time versus a single node, while exposing a single interface to external clients. We present the design, implementation, and evaluation of our system using a cluster of Intel x86 machines running Linux. We compare our algorithms with several well-known approaches and present scalability results for up to 10 nodes. Our best algorithm, Transaction Least-Work-Left (TLWL), achieves its performance by integrating several features: knowledge of the SIP protocol; dynamic estimates of back-end server load; distinguishing transactions from calls; recognizing variability in call length; and exploiting differences in processing costs for different SIP transactions. By integrating these attributes, our algorithm provides finergrained load balancing than standard approaches, resulting in throughput improvements of up to 24 percent and response times improvements of up to two orders of magnitude. We present a detailed analysis of how our algorithms significantly reduce