Circuit Identity Code is a traffic chanel id on A-interface and valid between MSC and BSC only. By knowing CIC MSC or BSC may correlate each signalling message from other peer on A-interface with appropriate call. There is switching matrix in BSC similar one in MSC but smaller. It is BSC related task to switch subslot on A-bis interface to subslot on A-ter interface (timeslot on A-interface) only during call time. There is no permanent static mapping a radiointerface TCH to A-interface TCH.