Toshiba Phone System

IP telephony network, but remote sites can't talk to each other?

My company has an Ip telephony network, that consists of 3com NBX, PIX fire wall, and fail over fire wall, Cisco switch, IP telephony sets, and cisco routers, Remote sites are connected to internet through SDSL cisco routers, but they can't talk to each other, while any remote office can talk to main office, and vise versa. If a remote office tries to call another remote one the other will here the ringing, but once he tries to answer, they can't hear each othe, Is there anybody can help suggesting some possible reasons.?

Public Comments

1. ohh boy... start with firewalls and open things up once you located the issue you can start to lock things down the cisco routers and that they are routing correctly, it's easier if you start with one office at a time...
2. This sounds like a firewall misconfiguration. Perhaps you have ports opened for A <-> B and A <-> C but not C <->B. Perhaps the firewall rules are too specific, or just overlook the remote to remote calls for all the ports needed. It may be that remote B needs to contact C and still needs to connect to A if the PBX is there.
3. The NBX sets up the call between two NBX phones and then drops out of the picture. Once the call is set up, its phone-to-phone and the NBX has nothing to do with it. So it's absolutely necessary that the remote sites be able to talk to one another for this to work. Each phone would have to have an IP address assigned to it for this to work, also. You cnnot use the NBX's IP-on-the-fly feature for this because that feaure assumes that all of the phones using it are on the same subnet.