You can use PRTG Network Monitor. It has the built-in ability to monitor VoIP between end points.
Feel free to contact me in case you want to discuss more on that.
The so called free NMS is not free in case you want support. All organizations where critical businesses processes have dependency on reliable IT Network and therefore, reliable monitoring, have to go for an NMS tool which is preferred by organisations whose business…
From my experience, I would suggest PRTG Network Monitor over both instead of getting into details as to which one of NETSCOUT and Solarwinds is better. Both Solarwinds and NETSCOUT are expensive. NETSCOUNT is into loggerheads with Gartner report. Gartner rate Solarwinds…