GSM - Architecture, Protocols and Services, Third Edition

Chapter 3. System architecture and addressing

System architecture

The fundamental components of a GSM network are shown in Figure 3.1. A user carries a Mobile Station (MS), which can communicate over the air with a base station, called Base Tranceiver Station (BTS) in GSM. The BTS contains transmitter and receiver equipment, such as antennas and amplifiers, as well as a few components for signal and protocol processing. For example, error protection coding is performed in the BTS, and the link-level protocol for signaling on the radio path is terminated here. In order to keep the base stations small, the essential control and protocol intelligence resides in the Base Station Controller (BSC). It contains, for example, protocol functions for radio channel allocation, channel setup and management of handovers. Typically, several BTSs are controlled by one BSC. In practice, the BTS and BSC are connected by fixed lines or point-to-point radio links. BTS and BSC together form the radio access network.

The combined traffic of the users is routed through a switch, called the Mobile Switching Center (MSC). It performs all of the switching functions of a switching node in a fixed telephone network, e.g., in an Integrated Services Digital Network (ISDN). This includes path search, data forwarding and service feature processing. The main difference between an ISDN switch and an MSC is that the MSC also has to consider the allocation and administration of radio resources and the mobility of the ...