Troubleshooting Steps for calls not answering on first attempt

[Chris Leslie]

Hi,

Before I go into great detail with the issue that we're facing I was wondering if anyone had some troubleshooting steps to help diagnose an issue where some calls coming in from a call queue will not answer when the staff pick up the phone that is ringing, it continues to ring on all the other phones in the queue (ring all) and won't answer unless they put down the handset and try again.

We're using version 15.5.15502 of 3CX hosted on Debian in AWS with full passes on the firewall tests.

The phones on this instance are Yealink SIP-T41P with the latest firmware.

The phones were originally set up as STUN but while troubleshooting we now have them set up using a Windows based SBC but the issues are still happening.

The local network the phones are using is a Unifi Security Gateway as the router with SIP ALG disabled. The modem is bridged so the USG is not creating any double NATs etc. Before SBC the phones were configured with static IPs and their internal SIP & RTP ports were forwarded manually.

Assuming we've done no troubleshooting, is there a decent set of steps that anyone can share for us to start over in case we've missed something or any additional information you think might be helpful in getting to the bottom of this?

Thanks.

 

[JohnS_3CX]

Hi Chris,

Without making any assumptions, one thing that may be happening is that the phone stopped being polled and just didn't get the message. By the time you put it back down it receives the next invite and you are able to pick up again.

So if this was the case, I go about it by seeing captures on the PBX and comparing them with captures on the phones to see if the CANCEL message reaches the phone in time. You could also try increasing the ring time to a very high value and see if that reduces the issue.

As a general precaution I would recommend to update to V16 with the new SBC as soon as you can. This will also give you access to newer firmware and templates, as well as the new queue manager framework. As always, create a backup first.