<p dir="ltr">Important is to send the media through two independent carriers - then you can be sure that your clock is compared against a high quality one.</p>
<div class="gmail_quote">On Apr 4, 2015 12:46 PM, "Regis M" <<a href="mailto:regis.freeswitch.org@tornad.net">regis.freeswitch.org@tornad.net</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Hi,<div><br></div><div>It's a very interresting test and conclusion.</div><div><br></div><div>I will try to build a similar environnement on my freeswitch to check some system :)</div><div><br></div><div>thanks</div><div><br></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">2015-04-04 2:16 GMT+02:00 Stanislav Sinyagin <span dir="ltr"><<a href="mailto:ssinyagin@gmail.com" target="_blank">ssinyagin@gmail.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">hi,<br>
<br>
Here are some test results which might be interesting:<br>
<br>
I've set up a test FreeSWITCH server at digitalocean (they use KVM),<br>
and originated test calls to some ITSP accounts. Each call played a<br>
test sound file (voice samples from ITU:<br>
<a href="http://www.itu.int/net/itu-t/sigdb/genaudio/AudioForm-g.aspx?val=1000050" target="_blank">http://www.itu.int/net/itu-t/sigdb/genaudio/AudioForm-g.aspx?val=1000050</a><br>
), and on the receiving end another FreeSWITCH server was recording<br>
the received session. The receiving server was on a XEN VM. Both<br>
servers talked G711 to their corresponding ITSP accounts.<br>
<br>
Then I compared the source audio and received audio in Audacity editor.<br>
<br>
The tests showed that the received voice wave shifts 20ms from the<br>
original sound every few seconds, randomly back and forward. This<br>
skewing was always present, regardless of ITSP and time of day.<br>
<br>
Then I moved the sending server to a XEN VM, and the waves appeared<br>
almost perfectly synchronized (there was a 5ms skew in one test, and I<br>
guess it's related to transcoding buffer, as the sound was obviously<br>
transcoded).<br>
<br>
The effect was always visible with a 30-second sample, and I also made<br>
additional tests with 2-minute samples.<br>
<br>
It would also be interesting to test this from a VmWare VM. If someone<br>
wants to run such a test, feel free to contact me directly.<br>
<br>
<br>
cheers,<br>
stan<br>
<br>
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