r sending an INVITE message from the MH to the CH. 17.5.2 System Architecture for Performance Evaluation For our case study, we have considered an architecture conceptually similar to IP-based 4G networks in terms of heterogeneity in access network technolo- gies. A logical view of the architecture considered is shown in Figure 17.4. The architecture is primarily focused on wireless mobile multimedia network- ing and is constructed around an IP core network (the Internet) with two different types of the access networks, viz. UMTS and WLAN. The UMTS Release 5 multimedia architecture [9] has been proposed by 3GPP to provide multimedia-based services in an all-IP environment. UMTS Release 5 defines GPRS/EDGE* radio access network (GERAN) as its access technology. We have assumed only GPRS access network due to its wide acceptance. GPRS networks are built on existing Global System for Mobile communications (GSM) networks by adding a new class of net- work nodes called the GPRS support nodes (GSN). A serving GPRS support node (SGSN) is responsible for mobility and link management, and deliver- ing packets to the MH under its service area. A gateway GPRS support node * Enhanced data rates for GSM evolution C 2009 by Taylor & Francis Group, LLC SIP-Based Mobility Management and Its Performance Evaluation (GGSN) acts as an interface between the GPRS network and the external packet data networks (the Internet, in this case). Home Location Register (HLR) and Visited Location Register (VLR) are two databases to keep user location information for mobility management. These databases are derived from legacy GSM architecture. A location register in the SGSN keeps track of the current VLR for a user. A salient feature of UMTS Release 5 standardization is the new subsystem, known as the IP Multimedia Subsystem (IMS) that works in conjunction with the Packet Switched Core Network (PS-CN) for supporting legacy telephony service as well as new multimedia services. The IMS enables an IP-based net- work to support both IP telephony s