[Freeswitch-users] KVM vs. XEN virtualization

Stanislav Sinyagin ssinyagin at gmail.com
Mon Apr 6 12:40:44 MSD 2015


I'm using the smallest $5 machines at DO in Amsterdam and London, and
Xen is on my colocated physical machine in Zurich.

I'm still collecting the statistics. It's all started when I had my
call generator at DO, and I noticed regular slipping frames on the
receiving side. The calls were definitely going through TDM links,
because I know the receiving side.

I'm still testing it. Sometimes I get slipping frames from the Xen
calls, but never such regular slips as I got with DO. Sometimes on a
DO host, the calls run quite fine, but those were on a weekend in the
middle of the night. I'll continue testing during the week.

What would be good, is to have a KVM machine where the physical host
is controlled, so that we can see its overall CPU load during the
tests.



On Mon, Apr 6, 2015 at 10:15 AM, Errol Samuels <ewsamuels at gmail.com> wrote:
> 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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