ain is composed of the two key elements that provide services that require dedicated circuits like many GSM services. These CS elements are Mobile Switching Center (MSC) and Gateway MSC (GMSC). The GMSC is used to establish connection to the Public Switched Telephone Network (PSTN) while MSC transfer calls between different RNCs. The PS domain is composed of the elements that utilize resources on a demand basis. UMTS connects to the PDN (Packet Data Network) through 1 After "freezing", a Release can have no further additional functions added. However, detailed protocol specifications may not yet be complete. In addition, OA&M specs and test specs may lag by some considerable time. Thus, all TSs (technical specifications) pertaining to a Release may not necessarily be frozen at the time the Release itself is functionally frozen. Core Networks and Operations Support Systems the serving GPRS support Node (SGSN) and Gateway GPRS support node (GGSN). The other elements in PS domain are DNS (Domain Name Server), DHCP (Dynamic Host Configuration Protocol), packet charging gateways, firewalls [2]. Beside the CS and PS specific elements, there are elements that are common to both domains. These elements are HLR (Home Location Register), and AUC (Authentication Center). Thus, the core network can also be split into three main functional areas [2-4]: Entities needed to support PS services (e.g., SGSN, GGSN, etc.) Entities needed to support CS services (e.g., MSC, GMSC, VLR (Visitor Location Register, etc.) Entities common to both types of services (e.g., HLR, AUC, etc.) Circuit Switched Elements MSC: The 3G MSC provides the necessary control and corresponding signaling interfaces like MAP (Mobile Application Part) and interconnection to external networks like PSTN. It also handles mobility management like intersystem handovers, supplementary services like call waiting, and CS data services like fax. GMSC: The gateway MSC (G-MSC) is the MSC that determines which visited MSC the subscriber who is being called is currently loc