Audio break up on Polycom VVX 500

[joeyd]

Hi,

Does anyone have any insight as to why the audio from a number of Polycom VVX 500 handsets would be breaking up randomly? Small installation with 8 handsets working through SBC, and 3CX hosted on AWS.

Firmware of the Polycoms are 5.6.0.17325 as recommended on the 3cx guide. Also, each handset has a computer plugged into the PC port.

Sonicwall TZ 470 firewall (sip transformations off, consistent NAT off, no port forwarding to sbc), Comcast xfinity internet 200M.

Thanks!

 

[JohnS_3CX]

Hi @joeyd

Please start by providing all the relevant info as per here:
https://www.3cx.com/community/threads/information-to-provide-when-requesting-help.67558/

Then, check whether the issue occurs for external calls only, or if it also happens when 2 internal extensions talk to each other.

 

[joeyd]

Thanks @JohnS_3CX, here is the info from the link.

Standard Annual 16.0.8.9
Debian I assume (AWS Lightsail)
AWS
PolyCom VVX 500
SBC
Bandwidth
Firewall checker: yes
Custom templates: no

The issue seems to only be with external calls. I've currrently enabled consistent nat, and increased the UDP timeout from 30 to 300 seconds on the Sonicwall. Hoping that helps. Any other ideas?

 

[JohnS_3CX]

Ok, so unless we have evidence that internal calls are affected, then the problem might be purely on the trunk.

In this case I would not suspect the Polycom being involved in the issue, and I would try to see if the problem is with the provider. If this is true, we would expect the following:

- Internal calls always working fine
- External calls would be breaking up on desk-phones, and soft-clients too
- Recordings of calls would also have the external audio breaking up (indicating that the phone is unrelated)
- Voicemails left by external callers might also have audio breaking up (further proof that it's a trunk issue)
- The Sonicwall should not make any difference (if the problem appears to be on the trunk side)

In this case you might want to check the following:

- The Lightsail machine has enough CPU/RAM resources (just as a precaution)
- Then contact your provider and inform them about the issue
- Take a capture from the PBX for a bad call if you can, and you can use this as evidence

 

[leejor]

Do the sets use a different Codec internally, than that supported by your provider? In other words, is 3CX doing transcoding?

 

[joeyd]

@JohnS_3CX Looks like a lot of packet loss between the SBC and 3CX, no? Or is this a normal amount of packet loss for 6 days uptime?

 

[joeyd]

Do the sets use a different Codec internally, than that supported by your provider? In other words, is 3CX doing transcoding?

Doesn't appear so, phone is showing PCMU as first, and the provider shows

• G711ulaw (PCMU), G729a, ILBC (will default to ptime 30)
• G711ulaw (PCMU), G729a (will default to ptime 20)

 

[JohnS_3CX]

Hi

You appear to have packet loss, and that would be sufficient to justify broken audio.

If you have any recordings I believe you will be able to confirm it:

- The remote caller audio will not be broken
- The audio coming from your users will be broken

The loss can be due to network issues, or it can also be related to the type of machine you are using.
What CPU and OS is the SBC on?

 

[joeyd]

Hi

You appear to have packet loss, and that would be sufficient to justify broken audio.

If you have any recordings I believe you will be able to confirm it:

- The remote caller audio will not be broken
- The audio coming from your users will be broken

The loss can be due to network issues, or it can also be related to the type of machine you are using.
What CPU and OS is the SBC on?

It's a raspberry pi 4 - 4GB, (standard raspbian install via their noobs download) connected to a dell N2024 switch. Internet - sonicwall TZ 470 using Comcast.

 

[JohnS_3CX]

OK, so just to eliminate any 3rd factors that the noobs install may have introduced, I would recommend to first prepare the Raspberry Pi using the 3CX supported method and disk image.
https://www.3cx.com/docs/installing-pbx-raspberry-pi/

Please read the entire guide and reinstall your SBC, noting that step 2 is where we link the supported SD card image, and at Step 5 you just select SBC instead of PBX.

Let me know if you have any questions and I will be glad to assist.