1 Way Audio on Remote Phones

[Matt Szalkowski]

We have a system with multiple remote sites using STUN. For some reason ever since upgrading to 15.5 SP6, they have issues where they start getting 1 way audio on the remote phones. The remote phones cannot hear anything, but the caller can hear them just fine.

Packet captures show the RTP getting sent to the phone, but the phones don't appear to be playing it, and a reboot of the phones doesn't help. I also tried the "PBX Delivers Audio" checkbox on my test extension to no avail.

I have tried a test remote phone here, with the latest firmware on the phone, but it makes no difference. The way I have fixed it is to restart the 3CX services and it begins working again. However the problem reoccurs after a day or two. Not sure what else to do here

None of our other systems have this problem, but we don't have anyone else using remote extensions..

Any thoughts?

Thanks!

 

[VoIPTools]

Note that 3CX expanded the number of RTP ports 9000 - 10999. Make sure you have opened these ports on your firewall, and I would run your firewall checker to confirm. That's where I would start.

 

[Matt Szalkowski]

Note that 3CX expanded the number of RTP ports 9000 - 10999. Make sure you have opened these ports on your firewall, and I would run your firewall checker to confirm. That's where I would start.

Thank you for the quick response. That was my first thought, however when I do a capture right from the desktop of windows running 3CX I do see both RTP streams in the capture and can play them.

The firewall checker does fail on SIP and the second range of RTP ports, but as near as I can tell, the traffic is making it through the firewall properly.

 

[Matt Szalkowski]

Thank you for the quick response. That was my first thought, however when I do a capture right from the desktop of windows running 3CX I do see both RTP streams in the capture and can play them.

The firewall checker does fail on SIP and the second range of RTP ports, but as near as I can tell, the traffic is making it through the firewall properly.

Just kind of thinking this through - I did a capture on the inside of the 3CX, but I did not get one on the outside of the firewall/router or outside of the remote phone to make sure it was making it out of the firewall properly and to the endpoint phone. If this problem resurfaces in a day or so I will need to do that to see what it looks like.

 

[cobaltit]

Well your capture should show you what ports are being used and what is being requested in the SDP. I find it odd that people are attributing the audio issues to the expanded ranges unless 3CX changed something in how they allocate the RTP ports. It used to be that they allocated them starting at the bottom based on concurrency so in theory the original range of 9000-9255 should do 128 calls before more RTP ports are needed. I haven't wire sharked any calls to see if this changed but I've also changed the port range prior to any upgrades so.

Anyways let us know what you see in the wire shark as far as the actual ports being used.

 

[YiannisH_3CX]

Hello @Matt Szalkowski

I would recommend opening the new ports on the firewall even if that is not that cause of the issue to avoid future issues with audio. After you pass the firewall checker see if the issue can be replicated.

 

[joemailey]

I didn't open the firewall reports on one of my sites, to see if it would affect anyone.

After a few days, remote users didn't get any audio. opening the ports resolved this.

 

[Matt Szalkowski]

Thank you all for the input, I've thrown it to the customer's Firewall/IT Management to resolve the Firewall Checker failure.

I will update with results.