Strange intermittent audio issues on 3cx Hosted PBX + SBC

[SOS IT]

Hosting: 3CX Cloud

Version: 18.0 Update 5 Pro

SBC Version:18.1.36

SBC Type: Raspberry Pi 4 8GB RAM

Phones: Fanvil X3U Pro with latest 3CX firmware

Hello,

This particular customer has an odd audio issue. We have a Sonicwall TZ370 firewall in place and Ubiquiti Unifi switches on the network. All phones are connected PoE. SIP ALG is disabled on the firewall.

They have Comcast Business 1250MB Down, 35MB Up.

This system has 8 extensions/8 desktop phones.

The audio issue is the sound is great most of the time but the audio will drop out completely for 1-2 seconds many times during a call. It usually starts after around 30-40 seconds but sometimes later in the call. No real pattern except that after it does it once it will keep doing it many times. The audio drop out is always the same amount of time 1-2 seconds.

Understandably the client is annoyed with it. This happens for both extension to extension calls and external calls. It does not matter if the call is coming from outside or starting from inside.

I have call recording turned on and it does record the dropouts of the audio which makes me think it is something on their network. Being a very small office they have 1 server, windows desktops/laptops, printers, the fanvil phones, and a handful for wifi devices like mobile phones. Nothing out of the ordinary.

The Fanvil phones do have singal bars, like on a cell phone, to indicate voice quality. We have noticed that the signal bars do drop to 1 (from 2) around the time the audio drop outs happen in some of our tests.

I am at a loss at what could be causing this. We run many 3cx hosted PBX for many customers with similar hardware/firewall setups without this issue.

Has anyone run into this before?

I am hoping someone has found a resolution in the past. Thanks in advance for any assistance!

 

[Charles_3CX]

Regarding your question, firstly, your setup looks good at first glance. The question now is, from where do these audio dropouts originate? VoIP provider, Internal network, etc.? Identifying this would require you to run packet captures on both the SBC (from your side) and us running captures on PBX (from our side) in tandem and gathering the logging from both the PBX and SBC in verbose logging mode to check.

As a first step, though, you can run an MTR test from the SBC by logging into the Pi's terminal to check the connectivity between the PBX and SBC.

Access the Pi via SSH and login, issue sudo su, and hit enter
then run:
1. apt-get update
2. apt install mtr -y
3. clear
4. mtr -4 <Enter__PBX_IP_here> (without the chevrons)

Wait until the mtr test starts and make a call. Then at the time of the audio dropouts, take a screenshot of the output. Press CTRL+C to stop the mtr test.

Since recording calls are enabled, the audio will pass through the PBX between an internal extension and extension calls using the IP Phones. This will allow you to see if there is any packet loss between the PBX and SBC, which may indicate an issue with your connection.

It is also worth checking with you through, as you mention, the IP phones have signal bars; which Fanvil phones are these, and what is their firmware level? Check and make sure they are on the let's 3cx firmware.:https://www.3cx.com/support/phone-firmwares/ also, how are these IP phones connected? Hopefully not wifi but rather hardwired correct?

 

[SOS IT]

Hello,

The audio issues are most certainly the local network since dropouts occur even extension to extension internal calls.

I will have to go back to the customer site to get the test run from the Raspberry Pi.

For the Fanvil phones they are running the latest Firmware from 3CX for the X3U Pro which is 2.4.7.5

They are hard wired PoE to a ubiquiti unifi switch.

 

[SOS IT]

Update: Running mtr from the Pi even without a call shows some "loss", first test was 2.2% on one comcast hop out of 1000 sent, second test was was the same for 1000 packets. Though it does show all packets sent making it past the "offending" node.

Not sure if this would affect it or not. Example attached.

 

[SOS IT]

I am also opening a ticket with Fanvil support. I do not know what else to do!