Remote phone keep going to no service

[dza]

I have several remote Yealink T42S phones connected to the internet using Yealink wireless adapters.

They are all configured the same way using direct SIP (STUN - remote). However, one phone recently started losing service. This issue began when the client's ISP changed their router.

I noticed that the client's IP address was getting blacklisted in 3CX management console, which kind of explained why the phone was losing service. ( not sure why it would get blacklisted in the first place)

Action taken so far: I added the client's IP to our whitelist in 3CX management console, factory reset the phone, reprovisioned it, and upgraded the firmware. However, after a few hours, it still goes to "No Service" again, and it needs to be reprovisioned manually by logging onto the phone interface and rebooting it from there. I can confirm that the phone remains connected to Wi-Fi when it goes to "No Service."

Do you have any idea what could be causing this issue and how I can fix it?

 

[SteveITS]

Avoid STUN, it isn't supported in v20. The T4U models can be router phones. Or, install the SBC software on a PC at the location.

Are the ports forwarded in the phone's router? SIP ALG disabled?

We had a client with a router phone, where ultimately they got the ISP to replace their router, since the phone worked elsewhere.

 

[JohnS_3CX]

Too many factors can act against the reliability of STUN phones to be worth the effort maintaining them.

If they are all at the same remote site, your best bet is to install a 3CX SBC
https://www.3cx.com/docs/3cx-tunnel-session-border-controller/

Once its up, factory reset the phones and add them anew to their respective extensions via the SBC this time and the problem should be resolved.