 Public Switched Telephone Network (PSTN). The medium class has the potential to provide a user experience similar to common wireless mobile telephony ser- vices. The best effort class includes the type of services that will provide a usable communications service but may not provide performance guarantees. The specification for the end-to-end media packet delay for the best and high classes of services is less than 100 ms, while for the medium and best effort classes, the delay is less than 150 ms and 400 ms, respectively. In fact, a handoff delay of more than 200-250 ms makes voice conversations annoying. Clearly, the handoff delay, being a component of the total end-to-end delay, should also abide by these delay limits. Thus, it is evident that for QoS-sensitive streaming multimedia traffic belonging to either the best or medium class, the handoff delay should be preferably less than 100 ms. In the rest of this chapter, we investigate the performance of SIP as a mobil- ity management protocol from the above perspective in a heterogeneous access networking environment akin to fourth generation (4G) wireless networks. In particular, we perform a case study of SIP-based handoff delay analysis using SIP to handle terminal mobility in an IP-based network. Two different types of access technologies, viz. UMTS and IEEE 802.11b-based WLAN, have been considered for the IP-based network. 17.5.1 SIP Mobility Support Apart from the session setup function, SIP inherently supports personal mobil- ity and can be extended to support service and terminal mobility [19,25]. Personal mobility enables a user to be found independent of the location © 2009 by Taylor & Francis Group, LLC SIP-Based Mobility Management and Its Performance Evaluation and network device. Terminal mobility, on the other hand, enables a user to change location or IP address during the traffic flow of an ongoing session. It can be explained with an example of an ongoing session between a mobile host (MH) and a correspondent host (CH) as follows. Each MH bel