“i am currently investigating a problem were calls on GSM are dropped with cause reason “recovery on timer expiry”. An initial investigation of the core network timer shows no evident problems with the timer settings however i from K15 traces of the A interface, i noticed that in most cases, the call drop occurs when NO connect ACK is recived from the MS. The call is connected normally however after some time, it drops with reason “recovery on timer expiry”. It seems that a timer is started when the msc sends the CONNECT message and it is stopped when CONNECT ACK is received. If no CONNECT ACK is received before expiry of this timer, the call is released. Did anyone see this type of behaviour before? Why is the connect ACK not being sent by MS (possible poor radio conditions?) Any help on this would be greatly apreciated. Network here is Siemens BR9.0″
I have the same problem , but im my case I see that the ms send connect ack but I don’t know if the MSC receive this message