A Flow-Based Traffic Model for SIP Messages in IMS

The IP Multimedia Subsystem (IMS) defined by the 3rdGeneration Partnership Project (3GPP) and 3GPP2 provides a platform for the provision of multimedia services with quality of service (QoS). In addition, this service architecture allows third-party vendors to create advanced multimedia and multisession services across wireless and wireline network access. The Session Initiation Protocol (SIP) supports the signaling and session management functions of these services; therefore, the SIP performance is critical to the services' quality of experience. Thus, in order to conduct an SIP performance evaluation, an efficient yet representative model for SIP signaling traffic is needed. In this article, we provide an in-depth flow analysis of a number of SIP session procedures defined in IMS and quantify the SIP signaling traffic at flow level. By utilizing the signaling flow analysis, the workload of servers can be predicted with a simple mathematical calculation. The complex correlation structure of the workloads across different signaling servers is naturally captured by the flow concept we introduced. This model also allows for flexibility when expanding the SIP session procedures in IMS networks. According to the simulations that we carried out using OPNET, the model we proposed is proven to be acceptable.