3CX Self-Hosted / Snom-Phones / Remote Extension via LTE WAN / Error: Stunserver is not answering

[LH74]

Hello,

we are using 3CX hosted on Azure since many month without any Problems. Provisioning mode of All Extensions is Direct SIP (Stun remote). Never had any Problems. Now one Office has only LTE-Internet (4G) instead of DSL. The Situation is as follows:

* Factory-Default Snom Phone requests for Login credentials
* Provisioning seems to be successful as the Extensions Name is displayed correct
* Registration Fails, the Snom Error log Shows: Stunserver is not answering
* BUT: Phone calls can be made (with bi-directional Audio), it does only takes a few seconds until the call is made. Even the PBX's Phonebook is available
* Receiving of phone calls is not possible, as (even after sucessful outgoing call) there phone does not register to the pbx.

What we have done already (all unsucessful):

• Test with different LTE-Routers
• Test with different snom-phones
• Checked, the Extensions Settings in Management Console: no restriction outside LAN
• Put the Phone's IP in DMZ of the LTE-Router
• Port Forwarding (LTE-Router) WAN to phones IP: 443, 5000, 5060, 5061, 5065, 5090, 6060, 7060

The only sucessful Workaround is to manually remove the stunserver in the Snom Phone. After that:

• Everything seems to be fine: Phone can be re-registered manually
• Phone calls can be made/received immediatly (without waiting some seconds)
• After outgoing Call the phone is immedialy unregistered, waiting app. 1 Minute, phone is registered again
• After Incoming Call the phone keeps registered.
• After there is any "Action" on the BLF's the phone is unregistered.
• After phone reboot we would have to manually remove stunserver in the phones Settings again

Any ideas, how to solve this strange Problem?

Best regards from Germany,

Lucas

 

[Saqqara]

Does the 4G have a fixed IP address, without this stun is not going to work - it is down to how the mobile companies handle their network , you can not do port forwarding

You will probably be better off , installing a SBC

 

[JohnS_3CX]

Hi Lucas,

In LTE scenarios the infrastructure is different VS SL scenarios.

Often you will find carrier grade NAT, which means the modem is not directly exposed to the internet and hence DMZ or port forwards will have no effect.

The only thing I can suggest in this case that might improve the situation, is to install a 3CX SBC at the site with the LTE modem and make some tests.

I can provide you with help if you wish to install an SBC.

 

[LH74]

Dear Saqqara,
dear John,

thank you so much, for this immediate Reply!

Now I understand, that there are differencies between LTE and SL. If there is only one Phone and no computer at this site, does it makes sense to install a SBC? I've heard there are ways to run a SBC without a Windows Computer, just a piece of Hardware, is that Right?

Regards,

Lucas

 

[Saqqara]

You can install SBC on a raspberry PI 3 model B+ https://www.3cx.com/docs/installing-pbx-raspberry-pi/

The version for PI4, is in technical review and should not be used in a live environment , but this is down to you if you want to install for one phone.

Instructions for Pi4, post#31 https://www.3cx.com/community/threa...ow-with-v16-update-6.75633/page-2#post-342847

 

[JohnS_3CX]

The Pi 3B+ would make a perfect solution for bypassing the NAT via 3CX SBC.

You can install it on a local Windows/Debian machine first at the LTE site to make sure the SBC can work in your scenario, and if you are happy then get a small Pi 3B+ and use it as separate hardware dedicated for this purpose.

 

[AWS2P]

In which country are you based , because in France we can subscribe to 4G Business offer from SFR for example , with Static public IP directly provided with Huawei Router and price is not so expensive.

Of course full PI ready to work can be bought for 70/80 €