One Way Voice!

[Garfieldone]

How is the topology setup? Is the server on the internet or local lan? From my experience it sounds as if the voice server is on the internet somewhere. What happens is that the firewall rules for one reason or another will filter out part of the traffic. This is the firewall on the router itself. Depending on how many phones will be on this network either those firewall rules need to be adjusted or turned off. Stateful Packet Inspection(common firewall technique on modems and routers) is also something that can accidentally filter it out.