Intermittent audio issues with T23G phones on V20 Update 7

[tech3x]

I’m running V20 Update 7 with an SBC on-prem and the PBX hosted in a private cloud. The environment includes a mix of older phones: T19s, T23Gs, T29Gs, T46s, etc.
This setup has been stable and working well for over 5 years with no issues.

Issue description​

Recently, we started experiencing intermittent audio problems involving T23G phones:

• When calling T23G → T23G (sometimes even on the same PBX), callers:
  • Can’t hear each other at all, or
  • Hear extremely garbled audio that’s unintelligible
• Sometimes the call starts garbled, other times it starts fine and degrades
• The same issue occurs when a T23G makes or receives external calls
• The problem is inconsistent and I haven’t been able to reliably reproduce it

Scope of the problem​

• Every instance of poor audio involves at least one T23G
• I do not see this issue when using T29s calling other non-T23G phones

Additional observation (possibly related)​

I’ve noticed unusual reprovisioning behavior on some T23Gs:

• Most phones reprovision about 32 times per month
• Several T23Gs are reprovisioning 300+ times per month
• One T23G was reprovisioning ~2,700 times per month
• When I removed that phone, another T23G (previously reprovisioning ~32 times/month) jumped to ~2,700 reprovisions/month
• Most T23Gs remain in the 32–60 reprovisions/month range

I’m not sure if the reprovisioning behavior is related to the audio issues, but the correlation seems suspicious.

Has anyone seen similar behavior with T23Gs, V20 U7, or excessive reprovisioning causing RTP/audio issues? Any ideas on where to look next would be appreciated.

 

[KyriacosS_3CX]

Hi,

How many entries does your phonebook have?

Phonebook size can be a problem with older Yealinks.

 

[ivank]

Hi tech3x, do you have verbose logs for that period when you witnessed 2700 reprovisions?
If not, please enable them, keep for a few days and share the logs with me. This amount is very suspicious, we need to find what triggers this in the first place.

 

[ivank]

Still you need to check the phonebook size first as Kyriacos already advised.
2700/months = 90 reprovisions/day and if it is consistent, it means some periodic process triggers this.
If the phonebook is too large, it is downloaded for some time, fails and repeats again and again.

 

[tech3x]

Hi,

How many entries does your phonebook have?

Phonebook size can be a problem with older Yealinks.

Screen shot attached, I think I have zero.

 

[KyriacosS_3CX]

Screen shot attached, I think I have zero.

And on the PBX?

 

[tech3x]

And on the PBX?

Screen shots attached, it's either 1 or zero unless I am looking at it wrong.

 

[KyriacosS_3CX]

Hi, we can probably safely say it's not due to the contactbook, so please review ivank's recommendations for further troubleshooting.

 

[Kevin Attard Compagno]

Are there custom phone templates involved at all?

 

[tech3x]

Are there custom phone templates involved at all?

Yes, but they are not being applied to the phones in question.

 

[Kevin Attard Compagno]

In the case of Yealink phones, the templates deploy 2 files; make sure that you are not deploying the same "y-file" filename with different content from the different templates

Ref: https://www.3cx.com/docs/custom-ip-phone-templates/

 

[tech3x]

Hi tech3x, do you have verbose logs for that period when you witnessed 2700 reprovisions?
If not, please enable them, keep for a few days and share the logs with me. This amount is very suspicious, we need to find what triggers this in the first place.

DM Sent