Hi Phaysal, what you mean lost sync..i think that happened different clock with other (maybe in nano second)?
if you mean lost sync is no clock in BTS, BTS will off, so all MS will handled by other BTS. In our system BTS have Clock generate (From GPS) ,BSC (From GPS) and MSC (From other Switching or Clock MASTER). and all subsystem have Clock Backup (aproximatly 8 Hours) for handled system if clock source off.