hi
We need to identify the pain areas and isolate them so that we can find out the exact cause/reason for this drop.
When the call is dropped are you seeing any logs in the router inline to drop/disconnect in the link connected to the remote site ?
Also any flaps on the link or any other kinda message ther in the log ?
Though not sure about the config in polycom do you have any setting pertaining to renegotiate the link/codec or any other parameters after every 60mins which might be resulting in the drop..
regds