Call one-way audio drop in middle of conversation


I have 2 Asterisk servers and on both I have the same isue. One is 1.6 and another is 1.4 version. On is behind NAT another isn’t behind nat.

Sometimes happen, that, when you are in the middle of the call, you can’t hear the person on the other side, but that person can hear you. Look at the picture, this is the end of the call (look at the seconds). Then I hangup the call and call it back.

Here is the call graph

Any idea what can be wrong?

Regards Andraž