The GSM network is divided into three major sub-systems,
being the Base Station Subsystem (BSS), Network and
Switching Subsystem (NSS) and the Operation Support Subsystem
(OSS) [5]. BSS is sometimes also referred to as the
GSM Access Network (AN) while NSS is conveniently called
the GSM Core Network (CN). The Mobile Station (MS) is
a device of utility to the subscriber which is considered to
be a part of the BSS and is used to access the services
provided by the mobile network. The BSS, responsible for
management of radio interface between mobile stations and all
other subsystems, consists of several Base Transceiver Stations
(BTS) controlled by Base Station Controller (BSC).