The BSC is the functional entity within the GSM architecture that is responsible for RR (Radio Resource) allocation to a MS (Mobile Station), frequency administration and handover between BTS (Base Transceiver Station) controlled by the BSC. The BSC function may be physically located with the BTS. If this is the case there is no requirement for the Abis interface, and a preparatory interface to map signalling and traffic destined for the MS may be employed.