 communicates with the core network over an interface known as the I interface. The location register databases that were found in GSM are broadly carried forward into UMTS. The Home Location Register (HLR) contains the subscriber information. It also contains information to enable changing and routing of messages to the current location of the mobile. It also allows for various location service related information to be accessed. There is the Authentication Centre (AuC) where data for each subscriber is stored. It essentially allows the user access to the network, checking elements such as the IMSI. Finally there is the Equipment ID Register (EIR). This database stores the Mobile Equipment Identities. The Mobile Equipment ID is the equivalent of the IMEI used in GSM. For simplicity these databases are often collectively called the Home Subscriber Server (HSS). While many of the early mobile telecommunications services were located around 900 MHz with developments such as GSM 1800 and GSM 1900 taking advantage of higher frequency allocations, the spectrum reservations are all around the 2 GHz region. For Frequency Division Duplex (FDD) the uplink frequency reservation is between 1920 and 1980 MHz and for the downlink it is 2100 to 2170 MHz. This provides two 60 MHz wide reservations. Reservations are also in place for possible Time Division Duplex (TDD) operation. One is a 20 MHz wide slot between 1900 and 1920 MHz, and there is another optional 15 MHz wide band stretching between 2010 and 2025 MHz. As the FDD option is the one on which the first services will be launched, the text will focus on this mode of operation. However, it is not expected that all frequencies will be available in all countries. As already mentioned the bandwidth allocation for each carrier or channel is 5 MHz. In line with other CDMA systems there are many mobile units transmitting within the same 5 MHz channel. The power of these is regulated by the base station or Node B SO that the strength of each of them is approximately the same and