AS5300: VOIP call, can't listen to answering party.

Question

I have a AS5300 running VOIP call without Gatekeeper, and my cisco is behind NAT.
Now the problem is, i can't listen to a particular country but answering party can hear me well.
More, this don't happen to the rest of the countries.
And, if tested with different AS5300 on else where IP (NAT) it's ok to this particular country.
How can i conclude it's not my error ?
P/S: i did a debug and found that all my voice is sent successfully to the answering party. But no return packet from them after connection.

Answer 1

I was getting the same problem , I did nat on router but it did work , so i used PIX instead of router. what PIX do is that it has the command fixup protocls which make it works.
let me explain you :
well H.323 put its source n destination packet inside the payload so when the distination router recieve the packet it looks to the inside one( payload adds) not the outer one that changed through natting. so the destination router doesnt know about the public add , he knows only abt the private address. so in this way the packets are not coming back.
Now I need to put router instead of router , can u explain me how is it working for other countries , it should works for any one.