1) Log in to the LMT and then select the faulty BTS on the Management Tree tab page. Determine the subrack No., slot No., and port No. of the BSC Abis interface board that is connected to the faulty BTS.
2) Choose BSC Maintenance > Maintain Transmission and Signaling > Interface Board Port Timeslot Loopback.
3) Set the parameters in the Timeslot Location area and then click Query.
4) Check whether the Loopback Status of timeslot 0 is No Loopback.
Y => The Loopback Status of timeslot 0 is No Loopback. The RSL link of the main BCCH TRX is not looped.
N => The Loopback Status of timeslot 0 is not No Loopback. The RSL link of the main BCCH TRX is being looped.