One sided voice using Mitel SRC and Wifi cordless phones

[Leon van Heerden]

We experienced the following symptoms at one of our sites usin the Mitel SRC recording Solutiuon and Wifi phones:

When dialing a Mitel 5212 handset, that has been configured to record using the Mitel SRC solution, using a Cordless WiFi phone, the call goes through, you can see all the signaling and details appear on the phones. When the person answers, the WiFi phone can hear the other person, but the person on the 5212, can't hear anything from the WiFi phone.

The SRC prints a Major event in it's logs: One-way Audio

We did a TCPDump on the SRC server and found that there was only UDP RTP traffic going from the 5212 to the Wifi and nothing from the Wifi to the 5212.

We tried enabling and disabling every setting on the SRC and found nothing made a difference.

Finally a new default installed SRC server was brought in to test with. When using the new server, everything worked correctly. Both sides could hear each other fine.

Comparing the settings between the server, we found that all the settings were the same except for the IP addresses.

As a final resort we removed the new SRC server from the network and changed the IP address of the old server to be the same as the new server's IP.

This resolved the issue. Now the audio was working correctly.

This points to something that is configured somewhere on the network were we had no control, preventing the Wifi traffic from going through.