T200 expiry represnts Layer-2 Failure. SABM/UA message is not received by MS/BSS. This might be Due to low coverage (as its a remote site) check Rx_Lvel during call drop. Further it can also due to Hardware Failure. Check if particular TRX is faulty. Further, T200 works with N200 (maximum retransmission times of frame I) and its value is different for SD/TCH/FACCH (in ms).