Grandstream phone receiver can't hear me

[atmomin]

We have numerous Grandstream 1625/1628 phones on many servers 3CX hosted, Google Cloud hosted, Amazon Lighsail hosted.

I have an issue with our Grandstream phones only on 3CX hosted. I can hear other side, but other side can't hear me. It's been working fine for years without issues. Looks like issue started this week or last weekend. We have used phones for numerous calls last week. Calls still work perfectly fine on 3CX App, inside Firewall, outside, everywhere. That's how we are operational right now.

I checked SIP ALG, I connected phone outside our Firewall. All 3 phones in office have same issue. Other client phones on Google cloud and Amazon Lightsail have no issues.

Performed all easily possible troubleshooting, Factory reset phones, reconfigured, restarted 3CX server, nothing works. Unchecked PBX deliver Audio checkbox, no luck yet.

Thanks any more tips.

 

[SweetAction]

Phones are connected to a SBC or STUN?

 

[atmomin]

STUN

 

[atmomin]

For someone who might face similar issue, I unticked PBX delivers audio, but didn't restart phone. I tried 1 phone on Google cloud server on temp extension, I faced same issue, then I noticed difference from other extension, it had PBX delivers audio unticked. I unticked on temp extension, it didn't work, then I restarted phone, calls started working fine.

Then after unticking PBX delivers audio, I restarted phone on 3CX Hosted, now external calls working fine. but internal extension to extension call still gets no sound on either side. But also noticed if I use 3CX App on one side and Phone other side internal calls work fine.

So, just phone to phone internal calls still not working.

 

[SweetAction]

Officially speaking, STUN with 3CX hosted is not support.

One way audio issues are almost always the same issue - routing related. The PBX and the phone need to pass traffic to each other that isn't modified by anything in the middle - regardless if that is SIP ALG or just the NAT device discarding packets because it has no destination in mind.

Your fastest way to resolution is a SBC. But if you wish to use STUN you will need to do a packet capture to determine what is happening to the audio stream so you can resolve it.

 

[JohnS_3CX]

STUN will appear to work for a while and suddenly stop one day out of the blue. There are just too many variables at play to list now, but if you wish to use remote phones in the most reliable way, please use a 3CX SBC.
https://www.3cx.com/docs/3cx-tunnel-session-border-controller/