The GSM network is comprised of the following components:
The GSM network incorporates a number of network elements to support mobile equipment. They are listed and described in the GSM network elements section of this chapter.
In addition, the network includes subsystems that are not formally recognized as network elements but are necessary for network operation. These are described in the GSM subsystems (non-network elements) section of this chapter.
GSM specifies standards for interfaces between network elements, which ensure the connectivity of GSM equipment from different manufacturers. These are listed in the Standardized interfaces section of this chapter.
For most of the network communications on these interfaces, internationally recognized communications protocols have been used
These are identified in the Network protocols section of this chapter.
The frequency allocations for GSM 900, Extended GSM and Digital Communications Systems are identified in the GSM frequencies section of this chapter.
GSM networks are digital and can cater for high system capacities. They are consistent with the world wide digitization of the telephone network, and are an extension of the Integrated Services Digital Network (ISDN), using a digital radio interface between the cellular network and the mobile subscriber equipment
The GSM system provides a greater subscriber capacity than analogue systems. GSM allows 25 kHz. Per user, that is, eight conversations per 200kHz. Channel pair (a pair comprising one transmit channel and one receive channel). Digital channel coding and the modulation used makes the signal resistant to interference from the cells where the same frequencies are re-used (co-channel interference); a Carrier to Interference Ratio (C/I) level of 9 dB is achieved, as opposed to the 18 dB typical with analogue cellular. This allows increased geographic reuse by permitting a reduction in the number of cells in the reuse pattern. Since this number is directly controlled by the amount of interference, the radio transmission design can deliver acceptable performance.