[Freeswitch-users] KVM vs. XEN virtualization

Sun Apr 5 14:47:58 MSD 2015

Yrs, jitter buffer was enabled. Here I'm pretty sure that we deal with the
clock skew.
On Apr 5, 2015 12:07 PM, "Brian West" <brian at freeswitch.org> wrote:

> Correct me if I'm wrong but is sounds like you've described jitter.  Did
> you test with the jitter buffer enabled?
>
> On Sunday, April 5, 2015, Regis M <regis.freeswitch.org at tornad.net> wrote:
>
>> nice work !!!  Thanks for sharing.
>>
>>
>>
>> 2015-04-05 2:37 GMT+02:00 Stanislav Sinyagin <ssinyagin at gmail.com>:
>>
>>> here we go:
>>>
>>> https://txlab.wordpress.com/2015/04/05/testing-rtp-clock-precision-on-a-virtual-machine/
>>>
>>>
>>>
>>> On Sat, Apr 4, 2015 at 4:26 PM, Stanislav Sinyagin <ssinyagin at gmail.com>
>>> wrote:
>>> > On Sat, Apr 4, 2015 at 1:03 PM, Regis M <
>>> regis.freeswitch.org at tornad.net> wrote:
>>> >> How do you check wavs together in audacity ?
>>> >
>>> > you just open two WAV files, align their starting position, and
>>> > visually check the waves. If there's a problem, you would see that
>>> > after few seconds, the waves are not aligned any more.
>>> >
>>> >> Can you send me 2 samples wav (send... and recorded) so I could see
>>> the 20ms
>>> >> diff that you exposed...
>>> >>
>>> >> Is there a way to automate the result checking, so it could help to
>>> monitor
>>> >> itsp quality
>>> >
>>> > Here
>>> > https://github.com/openpreserve/scape-xcorrsound/issues/17
>>> > this is a link to a tool which compares two sound files at the wave
>>> > level. You can also see the sound samples in the ticket.
>>> > The problem is, that currently this tool does not detect such slipping
>>> frames.
>>> >
>>> > I will also write a detailed article with examples, during the weekend.
>>> >
>>> >
>>> >
>>> >
>>> >
>>> >>
>>> >>
>>> >> 2015-04-04 12:53 GMT+02:00 Stanislav Sinyagin <ssinyagin at gmail.com>:
>>> >>>
>>> >>> 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.
>>> >>>
>>> >>> On Apr 4, 2015 12:46 PM, "Regis M" <regis.freeswitch.org at tornad.net>
>>> >>> wrote:
>>> >>>>
>>> >>>> Hi,
>>> >>>>
>>> >>>> It's a very interresting test and conclusion.
>>> >>>>
>>> >>>> I will try to build a similar environnement on my freeswitch to
>>> check
>>> >>>> some system :)
>>> >>>>
>>> >>>> thanks
>>> >>>>
>>> >>>>
>>> >>>>
>>> >>>> 2015-04-04 2:16 GMT+02:00 Stanislav Sinyagin <ssinyagin at gmail.com>:
>>> >>>>>
>>> >>>>> 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
>>> >>>>>
>>> >>>>>
>>> >>>>>
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>>> >>>>
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>>> >>
>>> >>
>>> >>
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>>
>>
>
> --
>
> *Brian West*
> brian at freeswitch.org
>
>
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