Cannot answer calls on Polycom VVX250

[john@biologisticsolutions]

We setup our system months ago and tested external and internal dialing. We left the system alone for a bit and upon recent testing, I can dial and receive outbound calls just fine, but internal calls cannot be answered on the IP phone. The calls can be answered within the desktop and smartphone applications, but they can only be rejected on the IP phones.

We do not have an SBC and did not need one when we ran the initial tests on the system. Could this issue be specific to the Polycom config? We are self hosting on premises.


We tested on a Yealink phone and all seems fine there - leaning into this being an issue specific to polycom

 

[JohnS_3CX]

Generally the only case where no SBC is needed is if the phone is on the same LAN and IP segment as the PBX.

You could always factory reset and reprovision the Polycom to ensure that you've started from a clean slate.

That being said, what happens when you lift the handset while the VVX250 is ringing?

 

[john@biologisticsolutions]

Thank you for getting back to me so quickly.

When the handset is lifted or the answer button is pressed on the VVX250, the called phone stops ringing, but the call remains unanswered. You can reject the call by placing the handset down or pressing "Reject," but the calling phone continues to ring. It appears that the answer function does not work at all on the VVX250 and any rejects are not received by the calling phone.

I have tried factory resetting and reprovisioning the VVX250. For comparison, the T48S phone works correctly. Calls can be made from the VVX250 to the T48S, but not from the T48S to the VVX250.

 

[JohnS_3CX]

I would suspect it is most likely related to your network setup. Enable "PBX delivers audio" on the extension options and try again.

 

[john@biologisticsolutions]

Thank you for the suggestion - No change in behavior upon factory resetting/reprovisioning and enabling the "PBX delivers audio" option.

Calls still can be answered on the T48S but not on VVX250

 

[JohnS_3CX]

Ok it seems then that you will need to investigate further, with logs and captures to see exactly what the phone is sending (assuming the device is perfectly healthy).

I would suggest at this stage to contact a 3CX Partner and get assistance in troubleshooting https://www.3cx.com/ordering/find-reseller/

My intuition points me towards this being a networking issue, especially if the phones and PBX are not on the same subnet, and if the switches/router/firewall has SIP ALG or internal NAT applied which can cause havoc if 3CX sees the phone coming from one IP, but it's declaring a different IP in the signalling (ACK not received). Also if the PBX has dual NICs and they are misconfigured, it could be contacting the phone on NIC1 and replying to it on NIC2 2 which may be unreachable. Just some food for thought.