I have a Cisco phone system that was recently installed. Everything seems to be working fine, but we are having issues with the system randomly dropping external calls. The call still shows as active but no audio can be heard. I've got a Gateway router 2821 model that handles all of the call routing, and Cisco Call manager 22.214.171.1240-2. VOIP to VOIP internal calls seem to be fine, and outgoing external calls seem to not have a problem, but incoming external calls are pretty hit an miss. Any suggestions?