I have a problem with no Audio on VoIP gateways. Specifically this is an H.323 gateway.
I have encountered this at several customers and tried a number of versions of code. IP routing is enabled.
And all best practices implemented.
There may be many reason why you have one way
1. You could have a codec missmatch and hence can
2. The ipaddress used for the return call leg may be wrong
and unreachable ( maybe loopback ip as I've seen this happen