A Traffic Model for the IP Multimedia Subsystem (IMS)

The IP multimedia subsystem (IMS) could very well be the panacea for most telecom operators. Defined originally as the core network for 3G mobile systems by the 3rd Generation Partnership Project (3GPP), the more recent releases have included interfaces to fixed line networks and wireless LANs. British Telecom is embarking on a 10 year long bold endeavor, called the 21st Century Network (21CN), to completely overhaul its core network to one that is based on 3GPP IMS. The ultimate goals are to reduce operational cost and provide converged services to its customers. At the heart of the IMS is the home subscriber server (HSS), the master database that holds all customer profiles. The two main protocols used for session control procedures are the session initiation protocol (SIP) and Diameter. Both are sent in clear text and very heavy weight. Although IMS promises an exciting world of converged services, the sheer amount of signaling traffic could prove to be too costly. Since there are no known large scale IMS networks, a representative signaling traffic model is still unavailable. We, at BT, have defined a signaling traffic model for IMS using the experience we gained through 21CN. The model quantifies the traffic and latency for various procedures defined in IMS, starting from the basic call flows. We present the model in this paper and also compare the IMS traffic with other traditional schemes and make conclusions on its efficiency.