I got a problem in my GSM network, we use both 900MHZ and 1800MHZ. The problem is the call is silent for a first time call. afetr two to three attempts then voice is ok. some times call is ok for more than 10 minutes also but for some calls it is silent for the B-number i.e one way speech. and call drops frequently. for some time it becomes ok then silence then ok, sometimes silence will not stop, and then you have to cut the call and call it again.