[Freeswitch-users] [Freeswitch-dev] VMWare voice quality

Fri Jan 16 11:00:56 PST 2009

Yes it's hard to trust virtualized stuff because you have no idea what they
skimp on in terms of realtime access.

I won't endorse using FS on a VM as i have not done it very extensively
beyond openvz but I can
point out a few reasons why it has a fighting chance.

FS uses a timer architecture designed to amplify the work of one timer
thread into every timer open
by FS.  This single thread uses the monotonic clock on the system to try and
perfrom a 1ms accurate loop.

This single loop updates a soft value for current epoch time and microsecond
epoch time with the goal
of (again) being as close as possible to being accurate to 1 ms.

The timer loop also has a global matrix to all of the timing intervals being
subscribed to by a timer open by FS.
The loop will tick a counter in each unique timing interval (10ms, 20ms,
60ms etc) and fire a conditional broadcast to all of the timers who are
blocking for a tick.  This is not perfectly accurate but close enough to end
up plus or minus 2ms in resulting rtp traces.

So as long as the VM will expose the syscall down to the real monotonic
clock rather than doing it's own soft timing technique you have a better
chance for success.

The other issue with VM is with vmware, the bridged networking mode seems to
send 2 of every RTP
packet to the channel resulting in garbled audio from the obvious timing
issue introduced from too many packets.

Anyway evaluating FS with a VM is a good way to get acquainted but, with all
the money saved choosing FS, many can afford to buy it a nice 8 core box for
it to live on and still have money left over to support the project or
ClueCon 2009 this august ;)

On Fri, Jan 16, 2009 at 2:17 AM, Kristian Kielhofner <
kristian.kielhofner at gmail.com> wrote:

> Speaking of networking...
>
> After timing that's the next "achilles heel" of RTP handing with
> virtualization.
>
> Very, very few of these platforms were designed to handle massive
> numbers of very small RTP packets.  Everything from interrupt handling
> on the actual ethernet adapter to getting the data into userspace
> within the virtual instance is worrisome:
>
> http://www.xen.org/files/xensummit_4/NetworkIO_Santos.pdf
> http://forum.openvz.org/index.php?t=msg&goto=11619&
>
> Interestingly enough the Xen paper makes it out to be really bad yet
> the OpenVZ post praises Xen's performance.  Without any real testing,
> who knows?  I just know that scaling 50pps per RTP stream (20ms
> packetization) can be difficult enough on native hardware, let alone
> [virtualization technology du jour].
>
> On Thu, Jan 15, 2009 at 5:02 PM, Remko Kloosterman
> <R.Kloosterman at mtel.nl> wrote:
> > Lot's of experience and suggestions here. Thanks.
> >
> > I believe it should be theoretically possible to have blip-free RTP
> > streaming through the appliance. Most windows ethernet drivers allow for
> > QoS packet scheduling. If the VMware network bridge driver honors this
> > and syncs the buffers at 20ms frames (or whatever frame size applies)
> > you should be able to schale up a bit and maintain low jitter.
> >
> > Anyone knows how the VMware network bridge exactly works?
> >
> >
> > -----Oorspronkelijk bericht-----
> > Van: freeswitch-users-bounces at lists.freeswitch.org
> > [mailto:freeswitch-users-bounces at lists.freeswitch.org] Namens Gregory
> > Boehnlein
> > Verzonden: donderdag 15 januari 2009 21:37
> > Aan: freeswitch-users at lists.freeswitch.org
> > Onderwerp: Re: [Freeswitch-users] [Freeswitch-dev] VMWare voice quality
> >
> >> To the contrary, we have had quite good results in virtualized
> >> environments and you don't really need timing that is that accurate to
> >
> >> make it work.
> >
> > If you don't handle RTP, I'm sure it is amazing. However, if you have to
> > do voicemail, stream audio from the server or do any kind of actual
> > time/latency/jitter sensitive processing, I don't care how much you tune
> > your hypervisor, it's never going to scale.
> >
> >> We work quite well on amazon EC2 for example.  There are 2 issues I
> >> know about with vmware, 1 is you need to set a setting on the host to
> >> extend somewhat sane clocks being available, the second is I have seen
> >
> >> issues with the bridged network adapter actually doubling up all
> >> packets causing very strange issues, I suggest not using bridged
> >> networking if you experience this.
> >
> > I've not seen this behavior on Vmware ESX 3.5u2. Maybe an issue on
> > Vmware Server or Workstation?
> >
> >
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>
>
>
> --
> Kristian Kielhofner
> http://blog.krisk.org
> http://www.submityoursip.com
> http://www.astlinux.org
> http://www.star2star.com
>
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-- 
Anthony Minessale II

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