reduce packet loss and handoff latency in [38], where the two separate registration databases main- tained by SIP and Mobile IP have been integrated to minimize the location update delay and hence packet loss. Alternatively, SIP has been combined with HIP [39] for a hybrid mechanism called the SHIP to solve the same problem. It has been reported [39] that the SHIP performs better in terms of handoff delay when compared to the SIP and Mobile IP scheme. In the latter scheme, handoffs need to be processed in both Mobile IP and SIP, and home agents redirect the packets until SIP re-INVITE process is completed. SHIP avoids the re-INVITE message in SIP and therefore, its signaling overhead is smaller. In addition, SHIP provides multi-homing support, which does not exist in hybrid Mobile IP and SIP. 17.7 Summary The selection of an appropriate protocol for the mobility management frame- work warrants careful consideration with respect to several factors. In this chapter, a framework of qualitative comparative study of the mobility protocols from the network layer perspective has been performed with the con- clusion that SIP is the most appropriate mobility protocol for next generation heterogeneous wireless networks. However, SIP suffers from some handoff per- formance issues that have detrimental effects to multimedia applications. We have investigated the handoff performance of SIP in a heterogeneous access networking environment and validated this claim. In particular, we have per- formed a case study of SIP-based handoff delay analysis using SIP to han- dle terminal mobility in a IP-based network. Two different types of access technologies, viz. UMTS and IEEE 802.11b-based WLAN, have been consid- ered for the IP-based network. Analytical results show that for WLAN net- works, the handoff delay is suitable for streaming media but for low bandwidth UMTS networks, the minimum handoff delay does not meet the specification of 100 ms. More precisely, handoff to a UMTS network from either another UMTS network or a WLAN, in