onsists of five major components, namely radio access network, transmission/transport network, core network, service element (Applications), OSS (operational support systems). The com- ponent of Information Technology which plays a supportive for the telecom network is not as such discussed in the book. (Radio Access Network) (RAN): The RAN connects the end user devices to the core network that is, it sits between the device and the core network. The term RAN is typically used in GSM/UMTS networks. An equivalent term in CDMA2000 systems is air interface along with those components governing the networking of base stations and their connection to the core network. The air interface is the radio-based communication link between the mobile station and the active base transceiver station. RAN consists of two main components namely BTS (Base Transceiver Station) or NodeB and BSC (Base Station Controller) or RNC (Radio Network Controller). A BSC/RNC serves multiple BTS/ NodeBs [1]. Transmission Network: Like its name, it provides the transmission of traffic from the user to mobile network and from the network either to PSTN or to another mobile user or to the Internet (or application servers). Transmission systems include microwaves, leased line, fiber, and SO on. Introduction Core Networks: Core Network lies between RAN and OSS. It can be either circuit switched for voice communications or packet switched for data services. The mapping between RAN to Core Network is one-to-many. Core Network elements consist of MSCs (Mobile Switching Centers), SGSN (Serving GPRS (General Packet Radio Service) Support Node), PDSN (Packet Data Serving Node), GGSN (General GPRS Support Node), and SO on. Each MSC, SGSN and PDSN can serve multiple BSCs/RNCs. PDSN and GGSN connect the users to Internet or third party application servers [1]. Service Element (Applications): In 3G networks, users can get access to external Packet Data Networks (e.g., Internet) or in-house applications that are present on separate servers via core network. OSS