There are always “gotchas” when working with Cisco Unified Communications systems, and they are not always obvious. UCCX (Contact Center) is no exception.

PROBLEM: A VPN Call Center Agent receives a call from the Contact Center. Upon answering the call, it either just drops with dead air, or the agent hears a fast busy.

ENVIRONMENT: The Agent uses IP Communicator to answer calls over the VPN.

First, let’s find out what does work:

• Testing and troubleshooting took a total of 10 hours. I looked at the gateway, the agent settings, Contact Center, etc. All looks normal, and operating as it should. The only error we get when doing an ISDN Q931 debug is “Resource Unavailable”, but only after the call was connected to the agent’s IP Communicator.

• The gateway can talk to the IP Communicator. Tested by setting up a DID, and dialing directly to the phone.

• IP Communicator can use the gateway to dial out. Tested by calling external numbers.

• Extension-to-extension calls work fine. 

So, by isolating what does work, we can start identifying where the problem occurs. In this case, we have ruled out everything except for communication between Contact Center and the IP Communicator. This was tested by using a script that will dial the phone from within Contact Center. Failed every time!

Still, after hours of testing, we could not identify where the problem was. It wasn’t until James Buchanan of Presidio Networks saw my Tweet on LinkedIn and mentioned an idea. Check the “Optimize for Low Bandwidth” option under the Audio tab of the IP Communicator preferences.

3 Cheers for Social Networking!!  There you have it! Removing the option allowed the communicator to talk on the same Codec (in this case, G.722) as Contact Center. Using the Low Bandwidth option forces Communicator to use G.729, which we apparently did not have the transcoding setup. Which, begs the question….. How were they working before?

Huge Kudos to James, who, by the way, has saved my rear-end on more than one occasion!