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

[Kristian Kielhofner]

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