No audio on extension to extension calls

[infinity5]

Hi All,

We have a 3CX v15 Linux system hosted on an OVH VPS server. We have 4 Yealink desk phones in the office connected as direct SIP extensions (3 x T22 and 1 x T26). When one extension calls another the called extension rings but when picked up there is no audio.

We also have some extensions registered to the 3CX client on PCs and Mobiles connected on the same network. If a Yealink phone calls one of those extensions there is audio.

Also if one of the Yealink phones transfers an external call to another Yealink phone there is audio when doing an attended transfer.

We've been using and configuring 3CX for some time but have never experienced this situation, is anyone able to point us in the right direction to resolve this issue?

Thanks in advance for your assistance.

 

[leejor]

Are all of the extensions on the same network as the server? You say they are connected as "direct SIP extensions". What exactly do you mean by this...they aren't actually registering with the PBX server?

In some cases, setting the extension(s) option to enable "PBX delivers Audio" will allow it to work, but, you should discover, and fix, what is actually causing this.

When doing a transfer, the call passes back to the PBX, which is probably why it works at that point.

Check the 3CX Activity logs to see if there are any error logs on one of the calls.

 

[infinity5]

No the server is hosted on a VPS in a data centre somewhere. I provisioned the phones using Direct SIP, the phones are provisioned and are able to make and receive external calls. One thing to note occasionally the Yealink phones will drop connection to the PBX for 20-30 minutes and then reconnect, the 3CX clients do not do this.

As all of the remote extensions are on the same LAN and there are 4, I am going to try setting up a Session Border Controller to see if that solves the problem.

 

[pact]

It's most likely firewall/nat issue.

3CX Clients will use the 3CX Tunnel by default, which will get around the NAT issue.

As inifinity5 suggested, setting PBX delivers audio will ensure all RTP packets go via the server, instead of attempting to route locally.

Or as you are going to try, setting up a local SBC should also correct the issue, as the phones will talk on the local subnet fine, then the SBC will perform the 3CX Tunnel connection to get around the potential NAT issues.

We have experienced similar issues with our hosted clients, another potential fix is changing the registration method of the Yealink phone to TCP instead of UDP, as we've found some router/firewalls do no handle UDP correctly.