[c-nsp] VoIP without QoS

[Frank Bulk]

Another point worth adding: increasing the size of the jitter buffer can
significantly reduce the audio artifacts due jitter.  If you can use
Wireshark to capture a days worth of calls and then examine the distribution
of latencies it may be possible to set a jitter buffer on the end devices
that masks the jitter problem.

Frank

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Robert Blayzor
Sent: Wednesday, May 23, 2007 4:38 AM
To: Nassess, George
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] VoIP without QoS

Nassess, George wrote:
> I am in the process of extending our distributed VoIP call center to a
> partner company, and their networking staff are extremely adamant that
> they do not wish to implement QoS on their remote LAN, the DS3 link that
> the voice traffic will traverse, or the core LAN in our shared
> datacenter. I am fairly well aware of the arguments on both sides of the
> debate of Mr. QoS (me) versus Mr. Excess bandwidth (them) but I wanted
> to know if there is anyone on the list who has actually deployed an
> enterprise VoIP solution without QoS, and whether the deployment was
> successful as an ongoing solution or if QoS had to be added at a later
> date. 


Excess bandwidth does not always guarantee good voice quality.  If you
just want something that "works", then sure, excess bandwidth may
prevent your calls from clipping or dropping.  Howoever it depends if
your target is carrier grade voice calls or "it just works".

Carrier grade voice calls insure that packetloss is none or nil and that
jitter is in an acceptable range where it does not cause audible
problems.  That means that per hop latency does not exceed 10ms per and
that one way is no more than ~100-150ms.

You can have all the excess bandwidth in the world, but bursty traffic
over a shared link without priority/LLQ will cause jitter and audible
noise in a VoIP call.  It all depends on how much the end users can
tolerate.

As for Vonage, that's a service that "just works".  Nobody uses Vonage
because the voice quality is "super", it's just acceptable.  I'm sure
compared to a cell call, it sounds great! ;-)

-- 
Robert Blayzor, BOFH
INOC, LLC
rblayzor\@(inoc.net|gmail.com)
PGP: 0x66F90BFC @ http://pgp.mit.edu
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I do not fear computers.  I fear the lack of them.  - Isaac Asimov
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