Solved 3cx sends INVITE to IP phones with same From and To header

[George Ts]

Hello,
I have noticed that 3cx sends INVITE requests to my IP phones, having the phone's number in the From and To headers.
Also, there is a Content-Disposition header which includes a "signal; handling required" value.
The Message Body is xml, as seen in the attachment.
Just mentioning this in case it helps.
It looks like the 3cx is "polling" the IP phones, some kind of keep-alive, but not sure if this is by default or configurable.
Some IP Phones reply with 200OK, soe others with 488 Not Acceptable Here (apparently the latter don't like .xml in the Message Body).

Any ideas what this is?

 

[StefanW]

this is uaCSTA to contact the phone to build a channel with the phone to drive it in CTI mode...
if a device can not speak uaCSTA then it has to decline the request with 488. All phones we can drive answr with 200 OK...

 

[George Ts]

All phones involved, either replying 200 or 488, are Yealink.
Apparently the model/FW version changes, this is why some of them do not support it.
Thank you very much for your prompt response.

By the way, is this configurable somewhere in the 3cx server?

 

[NickD_3CX]

3CX will always try to send a uaCSTA to supported IP Phones, that is why it is important to keep them on the latest supported firmware.