 technologies, namely EDGE (Enhanced Data Rates for GSM Evolution) and TD-SCDMA (Time Division - Synchronous CDMA)2 and was functionally frozen in March 2001. A major difference from R99 core network is that the MSC is split into two functional elements, MSC Server and Media Gateway Function (MGW). The details of these core network elements are described below and shown in Figure 8.2: MSC Server: The MSC server is a signaling element that provides the call control and mobility control of the MSC and it operates in the control plane. The MSC server sets up and manages the mobile originated and mobile terminated calls over the CS domain. It also contains the VLR which maintains the subscription data. Media Gateway Function (MGW): It resides in the user plane and handles the internet- working with the PSTN. The MGW terminates bearer channels from an external circuit- switched network and media streams from a packet-switched network. It interacts with the MSC server and GMSC server for resource control by using H.248 protocol. The MGW includes the necessary resources for supporting UMTS/GSM transport media. 2 TD-SCDMA is China's 3G system and is integrated in 3GPP as the 1.28 Mcps option in IMT-TD (International Mobile Telecommunications 2000-Time Division) and is called TDD low chip rate (TDDLCR). Core Networks and Operations Support Systems TD-SCDMA Radio Access Server Mobile Station Network GSM Base Station Mobile Station Subsystem (GSM BSS) Server Server CS Domain UTRAN PS Domain Radio Network Mobile Station Subsystem (UTRAN lu-ps GSM/EDGE Enhanced Base Station Subsystem Mobile Station (GERAN 3GPP Rel-4 Core Network Figure 8.2 3GPP Release 4 core network architecture. Reproduced from Willie C 2002 John Wiley and Sons, Ltd [1] Gateway MSC Server (GMSC Server): This element comprises the call control and mobility control parts of a GMSC. Signaling Gateway (SGW): The SGW performs signaling translation at the transport level between an SS7-based (Signaling System 7) transport signaling and an IP-based transport signa