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RE: VoIP QOS best practices
From: "chaim fried" <cfried () wireone com>
Date: Mon, 10 Feb 2003 14:14:00 -0700

Good point. Later version from the larger video-conferencing Gateway
manufacturers, seem to do a better job (better- not perfect) handling
reordering. So clearly there seems to have been issues with the
applications buffering itself. Out of order packets are considered lost,
so whatever you would put your tolerance threshold for loss will
determine your tolerance for ou of sequence? I would measure in terms of
.0x% for my customers, who expect "toll-quality" video.  

Based on the traces we've examined, most of the time it's not that the
latency is too much to be rectified with proper buffering. However,
again we don't want anybody reordering our packets.

-----Original Message-----
From: Leo Bicknell [mailto:bicknell () ufp org] 
Sent: Monday, February 10, 2003 11:44 AM
To: nanog () nanog org
Subject: Re: VoIP QOS best practices

In a message written on Mon, Feb 10, 2003 at 01:19:08PM 
-0500, chaim fried wrote:
happens). There is no reason to implement QOS on the Core. 
Having said 
that, there still seems to be too many issues on the tier 1 
with pacekt reordering as they affect h.261/h.263 traffic.

I've got a question about this issue.  Many networks reorder 
packets for a number of reasons.  At least once before I've 
attempted to measure the effects of this reordering on a 
number of forms of traffic, but I have never understood the 
particular effects on VOIP traffic.

Indeed, the two times I was asked to investigate this for 
video people it turns out the video receivers /had no ability 
to handle out of order frames/.  That's right, get one packet 
out of order and the video stream goes away until it 
resynchronizes.  Now, I realize reordering should not happen 
to a large percentage of the packets out there, but it also 
seems to me any IP application has to handle reordering or 
it's not really doing IP.

So what's the real problem here?  Are the VOIP boxes unable 
to handle out of order packets?  Do the out of order packets 
simply arrive far enough delayed to blow the delay budget?  
What percentage of reordered packets starts to cause issues?

       Leo Bicknell - bicknell () ufp org - CCIE 3440
        PGP keys at http://www.ufp.org/~bicknell/
Read TMBG List - tmbg-list-request () tmbg org, www.tmbg.org

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