3CX cloud, Yealink T42S stop every time and stop with connection

[CommunicationsNL]

Hi,
I'n new here and I hope that someone can help me.
I'm from the Netherlands and have a XS4all internet provider with a Fritz!box 7581 version. With that we are using 4 Yealink T42S phones (1 is on a other IP and 3 are on one and the same IP address) and we are using 3CX in the cloud (pbx).

Everything is going perfect. I install the phones, no problem, we have connection, we can call and other people can call us and it is all working. But now the problem is coming, 1 phone (the one who is NOT on the XS4all account) is working perfect, no problem and he is online for one week and it is great!!

The other 4 (who are on the IP with XS4all and the Fritz!box 7581) I have restart the Yealink already for 4 times and have connect them again with 3CX (pbx). Every time the connection will stop (after a couple of hours (7 or 10 or 24) and I see only RED dots on the Extensions page. I there someone who can tell me what is the problem and what do I have to do to let them online too.

Someone tell me that it is the Fritz!box and other tell me that it is the 3CX. But is there someone who can help me?

Thank you!

 

[CommunicationsNL]

Nobody who can help me?

 

[YiannisH_3CX]

Hello @CommunicationsNL

I am guessing you used STUN to provision the phones to the PBX from your description. If that is the case please make sure that under each extension you have assigned unique SIP and RTP ports to each phone. You will then need to port forward these ports on the fritzbox to the local IP of each phone. Re-provision the phones so that the new ports apply.
https://www.3cx.com/3cxacademy/videos/intermediate/configuring-remote-extensions/
Also make sure that SIP ALG is turned off on the Fritzbox as it could cause issues with connectivity and audio. If you still face the issue you might want to use an SBC at the remote site as it simplifies network configuration.
https://www.3cx.com/3cxacademy/videos/intermediate/configuring-remote-extensions/