[lug] VoIP quality issues and MTU

Daniel Webb lists at danielwebb.us
Sat Sep 24 00:04:27 MDT 2005


On Fri, Sep 23, 2005 at 08:55:38PM -0600, Lee Woodworth wrote:

> Hugh Brown wrote:
> >I don't know about MTU, but in a previous life they did voip over a vpn
> >and 80ms latency was the target the vendor said we needed to hit to
> >maintain average call quality.

> Hmmm. I see ping RTT of
>   82-88ms   qwest/DSL at EldoradoSprings <--> Qwest/ATM at Boulder(Earthnet)
>   85-90ms   qwset/DSL at EldoradoSprings <--> Mesanetworks at Longmont
>   35-36ms   Mesanetworks at Longmont     <--> Qwest/ATM at Boulder(Earthnet)
>   52-62ms   Mesanetworks at Longmont     <--> www.google.com
> Looks like home based VOIP might have quality issues if the
> qwest/DSL RTTs are the norm.

They might have been talking about jitter (max latency minus min latency) and
not latency, but I'm not sure.  I do have enough latency with my VoIP setup
that I sometimes notice it (it's typically 120-140 ms ping), but that's
probably because I'm using a provider in Michigan (Nufone.net) on a fairly
slow DSL modem with bad copper heading out of my neighborhood.  I think
audible jitter is a much worse problem than latency unless the total latency
gets too bad (0.4 seconds or so).  If you haven't heard it, it sounds sort of
like a cell phone call that's just about to go out, except the dropouts are
more rapid with shorter duration.  You can still make out what the other
person is saying most of the time, but it's extremely unpleasant to listen to.
I suppose it can sound many different ways depending on the pattern of the
jitter, that's just what I've heard on my line.




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