Vumeter for chanel

I have an extension e.g 100003 and there is a “talking” with extension e.g. 100004 and I would like to see vumeter for it. Please notice that the two extension are useing SIP softphones.

Could anyone describe how to do it step by step?

If you have a managed switch (or an old hub) you can setup a SPAN port to replicate the RTP data and feed it into an analysis tool:

Any other idea?

How much cost this tool?