GSM BASE STATION SYSTEM (BSS)
The BSS provides the air interface between the MS and the Mobiles services Switching Centre (MSC) and comprises of 3 constituent components, which are:
Base Transceiver Station (BTS)
Contains the antenna and RF Component; supplying a digital interface between the MS and BSS. As well as supplying the air interface for the BSS the BTS can control certain functions for the system. If increased coverage is required within a given area the BTS can be configured to support more cells to meet this demand.
Base Station Controller (BSC)
The BSC is the brains of the BSS, not only does it provide a link between the terrestrial links from the MSC to the air interface, but carries out control functions for the system. The digital-switching matrix used to control the flow of traffic also performs handovers between radio channels, on the BTS’s, without involving the MSC.
Transcoder Rate Adaptor Unit (TRAU)
The TRAU can be located either with the BSS or co-located with the MSC. The TRAU enables the use of lower rates (32, 16 or 8 kb/s) over the A-bis interface instead of the 64 kb/s ISDN rate for which the MSC is designed.
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