A client of mine had been having some difficulty with their Cisco VoIP system.  Their remote gateway would disconnect from their Call Manager system in the early evening and stay down until the following morning.  This became a daily occurrence.  After working with Cisco(who has pretty good support) they determine it was a TCP disconnect that was happening and recommended checking the network topology between the gateway and the Call Manager.  My original suspicion was that it was not the gateway but the Call Manager except the company’s IT staff at the Headquarters location claimed it was the phone carrier’s problem.

Once I finally got them to realize it was within the network between the two locations, they decided to remove the VoIP traffic from the traffic accelerator and the customer has not had any further problems.  If you find yourself in a similar situation check the connections using the debug features within Cisco products(if you are using them) and check your network traffic using a network analyzer.    It might save you a lot of time and get your clients back up to 100%.