In GSM the Base Station System is a term given to a BSC (Base
Station Controller) and the BTS (Base Transceiver Station) associated
with it. The number of BTS associated with a BSC is dependent on the
manufacturer. Although not mandatory, through interpretation of the Abis
interface standard BTS and BSC employed within a BSS will always be
supplied by the same manufacturer.
The BSS is the physical equipment used to give radio coverage to a
determined geographical zone called a cell. Functionally, a BSS is
subdivided into BSC and BTS

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Yes a BSS is subdivided into BSC and BTS.Thanks

This is very important ...............