 basic modes FDD and TDD, variable transmission rates, intercell asynchronous operation, adaptive power control, increased coverage and capacity, etc. W-CDMA also uses the CDMA multiplexing technique, due to its advantages over other multiple access techniques such as TDMA. W-CDMA is merely the air interface as per the definition of IMT-2000, while UMTS is a complete stack of communication protocols designated for 3G global mobile telecommunications. UMTS uses a pair of 5 MHz channels, one in the 1900 MHz range for uplink and one in the 2100 MHz range for downlink. The specific frequency bands originally defined by the UMTS standard are 1885-2025 MHz for uplink and 2110-2200 MHz for downlink. UMTS System Architecture A UMTS network consists of three interacting domains: Core Network (CN), UMTS Terrestrial Radio Access Network (UTRAN) and User Equipment (UE). The UE or ME contains the mobile phone and the SIM (Subscriber Identity Module) card called USIM (Universal SIM). USIM contains member specific data and enables the authenticated entry of the subscriber into the network. This UMTS UE is capable of working in three modes: CS (circuit switched) mode, PS (packet switched) mode and CS/PS mode. In the CS mode the UE is connected only to the core network. In the PS mode, the UE is connected only to the PS domain (though CS services like VoIP (Voice over Internet Protocol) can still be offered), while in the CS/PS mode, the mobile is capable of working simultaneously to offer both CS and PS services. The components of the Radio Access Network (RAN) are the Base Stations (BS) or Node B and Radio Network Controllers (RNCs). The major functions of the BS are closed loop power control, physical channel coding, modulation/demodulation, air interface transmissions/reception, error handling, etc., while major functions of the RNC are radio resource control/management, power control, channel allocation, admission control, ciphering, segmentation/reassembly, etc. The main function of the Core Network (CN) is to provide switc