[c-nsp] VoIP without QoS

[jp]

There's more to wireless than 802.11 stuff.

Alvarion claims 40k pps with their VL and Breezenet-B gear. I haven't 
tested their claims, but they definitely do a lot better than normal 
802.11b gear.

On Sat, May 26, 2007 at 04:46:44PM -0500, Dan wrote:
> Well I really have no choice but to use the wireless system that we 
> have.  We don't have any fiber systems out here that we can use.   You 
> say after about the 7th conversation is added, but about how many pps do 
> you think is the limit?  I don't have a lot of experience with this, but 
> knowing the limit might be helpful for the future.
> 
> Thanks,
> Dan.
> 
> John Osmon wrote:
> > It's certainly not as rigorous as one might hope, but it does explain
> > why common VOIP applications running over 802.11b start to fail when
> > around the time the 7th conversation is added to the mix.  Which is
> > quite consistant with empirical evidence I've collected, and anecdotal I've
> > had from others.
> >
> > My main point is that if the transport is prone to congestion with a
> > (relatively) small number of pps, it isn't good candidate for VOIP
> > communications.  The commonly found wireless schemes in use today fall
> > into this category of transport.  We'll see things get better as time
> > goes on, but the current crop of wi-fi gear simply isn't suited for VOIP
> > except in very spcific situations.
> >
> > I almost feel sorry for the WISPs that have built out neworks with 
> > 802.11b backahul links.  I've *seen* some of them staring at MRTG
> > graphs saying "but there's less than 1 Mbps on that link!  We can't
> > be the cause of your VOIP problems..."  As we all know -- the pps 
> > numbers are more imporportant than the bandwidth nubmers in most 
> > situations.
> >
> > This has drifted too far from the 'c' in 'cnsp' -- I'm going to go back
> > to lurking...
> >
> >
> >
> > On Sat, May 26, 2007 at 11:51:42AM -0500, Frank Bulk wrote:
> >   
> >> In the paper: "To generate a 64 Kbps flow, 64 bytes packets were sent every
> >> 8 milliseconds."
> >>
> >> This is not how the G.711 codec works...it's normally a 20 msec
> >> packetization rate resulting in ~220 byte frames (sans 802.11 headers, I
> >> believe).  I've seen too much undergraduate start with faulty assumptions
> >> such that the results are bogus.  The only thing these guys have proven is
> >> that lots of small packets cause latency and jitter when the link becomes
> >> saturated.  No surprise there.
> >>
> >> Regards,
> >>
> >> Frank
> >>
> >> -----Original Message-----
> >> From: cisco-nsp-bounces at puck.nether.net
> >> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of John Osmon
> >> Sent: Tuesday, May 22, 2007 11:21 PM
> >> To: cisco-nsp at puck.nether.net
> >> Subject: Re: [c-nsp] VoIP without QoS
> >>
> >> On Tue, May 22, 2007 at 01:47:15PM -0500, Dan wrote:
> >>     
> >>> We have a voip system we have been running in our department now for
> >>> about a year.  Only 12 phones, connected through various wireless links
> >>> with throughput of up to 40mbit.  Speed is definitely not an issue for
> >>> us, but we notice glitches with the quality on an ongoing basis.  We are
> >>> currently implementing qos and are wondering what is the best way?
> >>>       
> >> Most common wireless solutions don't really like a lot of small packets.
> >> They tend to have too much overhead in the protocols, and you if you're
> >> pushing small packets, you hit a pps limit long before anything comes 
> >> close to using up the bandwidth you think is available.
> >>
> >> While trying to research why VOIP over wireless networks, I ran into
> >> this paper:
> >>    http://www.it.uc3m.es/~acuevasr/publicaciones/LCS06.pdf
> >>
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> >>
> >>     
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> >   
> 
> 
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