SBC instability

[stuartpgs1]

I am new to the world of forums so apologies if my question is ignorant or badly formed. We are currently self hosting 3CX sites.

3CX SBC Stability – Desk Phone vs Dedicated Device

Looking for some real-world feedback from others running multi-site 3CX setups.

We’re seeing frequent SBC tunnel drops (Event 4102) across a few sites — in one case averaging 30+ Up/Down events per day. Symptoms include intermittent one-way audio and occasional call instability, despite moderate call volumes and passing firewall checks.

One common factor is that the SBC is currently hosted on Yealink desk phones ( normally T43 U) rather than a dedicated device.The sites are small, less than 10 users

For those with similar environments:

• Have you seen instability when using phones as the SBC?
• Did moving to a dedicated SBC materially improve reliability?
• How stable should a healthy SBC tunnel be in practice?

Leaning toward standardising on dedicated SBC hardware, but keen to hear others’ operational experience before making the change.

 

[NikosT_3CX]

@stuartpgs1 Are the phones on the correct and tested firmware ?
Check here :

https://www.3cx.com/docs/phone-firmwares/

Also, if for example you reboot these phones, are they stable for X ammount of time and then they start again ?
How many normal phones and BLFs do you have behing them ?

 

[bitn2]

How many BLF keys are configured on the phones? The T43U is not the strongest hardware to handle this.

 

[JohnS_3CX]

• The T43U should be on LAN not WiFi
• You should not overload it by hosting too many phones behind it (keep it to 2-3 phones)
• The amount of BLFs matter: 10 BLFs each is not the same as 100 total for example
• Network conditions matter: if the phone experiences a network storm, it will start dropping packets
• Internet connection matters: solid connections over fiber/DSL/cable are more reliable than LTE links or other wireless tech.

Using a phone as a router is fine when it serves itself and a few more low traffic phones.

But a dedicated SBC is practically always a better solution if you have more than a handful of phones.

 

[stuartpgs1]

Firmware is as per the recommended list. We update them prior to installation. The networks are very simple in their architecture, and on the particular problem network I have at the moment there are a total of three phones, also what I notice is the SBC changing between the two desk phones on site. There are 4 BLFs configured on each phone.

We have changed the ISP, The router, but the problems still exist.

 

[Alphabetic]

I would check the phone has a static IP address and its not something like short DHCP lease times.

 

[JohnS_3CX]

also what I notice is the SBC changing between the two desk phones on site

what does that mean?

 

[stuartpgs1]

The SBC is up and down across multiple extensions, here you can see 1001, 1002

 

[stuartpgs1]

I think thus more than one Phone on a site is acting as the SBC

 

[bitn2]

This looks like you have more than one sbc installed.

 

[SteveITS]

> How stable should a healthy SBC tunnel be in practice?

Normally, up 24x7 unless there's a connection drop at either end.

Especially if it's multiple router phones I expect you have sporadic packet loss at either this location or the 3CX server if multiple/all locations drop at the same time. Try a "ping -n 1000" to various IPs...3CX server if it answers: local router LAN IP, 8.8.4.4, ISP WAN gateway, etc.

 

[Kevin Attard Compagno]

How about some simple numbers to better explain your scenario? You have 2 router phones (192.168.0.2 and 192.168.0.5) apparently trying to keep their connections live to your PBX. Are there others? Also, how many phones are passing their connections through these router phones?

 

[Ronaldvdv]

View attachment 50856
The SBC is up and down across multiple extensions, here you can see 1001, 1002

So from the screenshot you have two router phones on that specific location. Both go offline at the same time. For me it looks like a network or power issue.

 

[stuartpgs1]

what does that mean?

Hello John

I have check and all phones on this site are set up as SBC. Do you think that this could be the route of the issue.

How about some simple numbers to better explain your scenario? You have 2 router phones (192.168.0.2 and 192.168.0.5) apparently trying to keep their connections live to your PBX. Are there others? Also, how many phones are passing their connections through these router phones?

Hello Kevin

The site is very simple. There is an Omada Wifi Gateway connected to BT Sogea 80/20. There are 2 x wired Yealink T43U and 2 x AX83 Wifi phones, there are two access points.

All four phones are set up as SBCs. Everything is brand new.

Issues include one way audio, poor call quality, poor call volume and dropped calls.

 

[JoshWS]

Hello John

I have check and all phones on this site are set up as SBC. Do you think that this could be the route of the issue.

Hello Kevin

The site is very simple. There is an Omada Wifi Gateway connected to BT Sogea 80/20. There are 2 x wired Yealink T43U and 2 x AX83 Wifi phones, there are two access points.

All four phones are set up as SBCs. Everything is brand new.

Issues include one way audio, poor call quality, poor call volume and dropped calls.

Hi Stuart,

We have had a few issues with the AX83H wifi phones being a router phone. We find that if we put them behind another hardwired router device or SBC we have much greater stability and quality

 

[Kevin Attard Compagno]

So it's just 4 devices. And the SBC up/down messages are about the "cabled" phones.

EITHER you have a VERY high level of traffic trying to to traverse the LAN-to-WAN edge device - in which case you need to consider increasing bandwidth (or if really desperate, DSCP traffic tagging, a whole other type of complexity)

OR you have networking issues at a relatively low level - think cables, router stability, general internet connectivity.

This is NOT a 3CX-centric issue.

 

[stuartpgs1]

There is definitely not a high volume of traffic. New ISP, New Router.

Old cables...

 

[Alphabetic]

Does the phone have a static IP? If not, does the problem go away when it does.

 

[stuartpgs1]

Phones have a static IP

 

[SteveITS]

Issues include one way audio, poor call quality, poor call volume and dropped calls

I don’t think you said above but does the 3CX firewall checker pass? Note it will drop active calls.

Did you test for packet loss as I suggested?