hi, Here are some test results which might be interesting: I've set up a test FreeSWITCH server at digitalocean (they use KVM), and originated test calls to some ITSP accounts. Each call played a test sound file (voice samples from ITU: http://www.itu.int/net/itu-t/sigdb/genaudio/AudioForm-g.aspx?val=1000050 ), and on the receiving end another FreeSWITCH server was recording the received session. The receiving server was on a XEN VM. Both servers talked G711 to their corresponding ITSP accounts. Then I compared the source audio and received audio in Audacity editor. The tests showed that the received voice wave shifts 20ms from the original sound every few seconds, randomly back and forward. This skewing was always present, regardless of ITSP and time of day. Then I moved the sending server to a XEN VM, and the waves appeared almost perfectly synchronized (there was a 5ms skew in one test, and I guess it's related to transcoding buffer, as the sound was obviously transcoded). The effect was always visible with a 30-second sample, and I also made additional tests with 2-minute samples. It would also be interesting to test this from a VmWare VM. If someone wants to run such a test, feel free to contact me directly. cheers, stan