[Freeswitch-users] KVM vs. XEN virtualization

Mon Apr 6 12:15:19 MSD 2015

Good job and Thanks for sharing!

KVM at digitalocean.com, Debian 7 64bit, FreeSWITCH 1.4.15: bad precision

As someone who has been using KVM for a few years and has just migrated
about 20 VMs across to Digital Ocean about 6 weeks ago I admit I am a
little concerned about this finding.

Just out of curiosity can you tell me the specs of the VM that you tested
with and which DO Datacenter?  I am using NYC3 so perhaps and I will do
some tests as soon as I have some time.

With regards to Xen was this at Linode or inhouse?

Thanks

Errol

On Sun, Apr 5, 2015 at 1:37 AM, Stanislav Sinyagin <ssinyagin at gmail.com>
wrote:

> 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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> >>
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>
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