There are two things of communication that needs to be allowed for a call to be in full working order. First both of the parties in the call need to be able to communicate with the CM system(s) for signaling, then when the call is established both of the parties in the call need to be allowed to communicate directly with each other for the media traffic. By the sound of what you describe the later is not allowed and that’s why you cannot hear anything in the call. There are very good resources with documentation for what ports various parts of the Cisco UC system requires. Have a look at these and let your firewall administrator know what to allow. That should solve your problem.
@Simon Roberts wrote:
I've been using this article which defines ports that need to be open in various scenarios. What it doesn't seem to cover is the scenario of an internal network separated by a firewall i.e. GlobalProtect.
From a communication point of view there is really no difference what you'd need to allow regardless of topology. All the ports listed in the document is needed to be let through whatever device you have that would block it. Using Expressway to connect disconnected, or at least not fully connected, networks is an option, but you should know that there are limits to how many clients you can have connecting via one Expressway pair. This can be expanded up to a point by adding more nodes to the C and E clusters and by having multiple entities of Expressway clusters.
