tween the network elements of homogenous wireless system. In the case of roaming, when a subscriber moves outside the range of an unlicensed wireless network to which they are connected, the GANC and handset facilitate roaming to the licensed outdoor network [1]. 11.9.1.2 IMS Based FMC Currently there is a strong push from all the circles in the telecom industry on IMS-based FMC. The creation of IMS-based FMC is a two step process which includes both short-term and long-term solutions. In the short term we will see Voice Call Continuity (VCC) support with IMS and in the long run IMS as an amalgamation platform for both wireline and wireless worlds. 11.9.1.2.1 IMS-VCC (Short Term) IMS-VCC supports the use of a single phone number (or SIP identity) as well as handover between WLAN and cellular networks. It specifies how to handle call handoffs between circuit-switched (CS) and IP network environments. At a high level the key component is the VCC application server which needs to be added to the IMS network to enable IMS-VCC as shown in Figure 11.15. IMS-VCC has been added to 3GPP Release 7 to address service continuity in different access modes. VCC Voice Call Continuity that provides capabilities to transfer voice calls between the circuit switched system (GSM/UMTS) and the IMS. 3GPP TS 23.206 [18] and 3GPP TS 24.206 [19] specifies VCC functional architecture, information flows and protocol details. However, the emergency calls will remain in the domain in which those were originated, regardless of changing conditions that might dictate domain transfer for normal calls. The VCC architecture as shown in Figure 11.16 reuses many existing elements in both the CS domain and IMS. The architecture shows the VCC Application comprises a set of functions. These functions are required for a VCC UE to establish voice calls and control the switching of the VCC UEs Access Leg6 between the CS domain and IMS while maintaining the active session. The four key entities of VCC Application 6 Access Leg is a call control leg between 