The person I am talking to cannot hear me

I am running the AsteriskNow with FreePBX 2.5.1.5

I can be in a phone call when all of a sudden the other person cannot hear me. Once that happens, if I make a call, the other person cannot hear me. When I get a call, the phone system works again and both parties can hear each other.

Can this be the result of the codec? The system has been running fine with the aastra phones for about 2 weeks now. Then all of a sudden, this begins to happen.

How can I check this out? In the GUI there is no way to specify any codecs to use. Also, there is no way to add or verify the codec that is being used…

Assistance is much appreciated.

Thanks,
Mike

Normally one way audio is related to a NAT firewall. Are the phones or the Asterisk server behind a NAT connection. It could be the the audio stream is trying to re-invite and failing possibly.