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Re: VoIP QOS best practices
From: "Stephen Sprunk" <stephen () sprunk org>
Date: Mon, 10 Feb 2003 16:20:39 -0600


Reordering per se doesn't affect VoIP at all since RTP has an inherent
resync mechanism.

Reordering is also unlikely, since each packet is sent 20ms or more apart;
I'm not aware of any network devices that reorder on that scale.

S

----- Original Message -----
From: "Leo Bicknell" <bicknell () ufp org>
Sent: Monday, 10 February, 2003 12:43
Subject: Re: VoIP QOS best practices


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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 networks
with pacekt reordering as they affect h.261/h.263 traffic.=20

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?

- --=20
       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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