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Last Mile QoS WAS: RE: QOS or more bandwidth
From: Nathan Stratton <nathan () robotics net>
Date: Tue, 29 May 2001 15:39:40 -0400 (EDT)


On Tue, 29 May 2001, Pete Kruckenberg wrote:

A 1536-byte frame has a fairly significant impact (~8ms) at
1.5Mb/s. QoS appears to have diminishing return as you move
beyond 45Mbps, at least as far as multi-service networks go.
Maybe QoS isn't necessary or useful in the core if you have
line-speed switching and no congestion on an OC-X/DWDM
network.

It has even a larger impact on a 128K frac T1 (~93ms). QoS is a big help,
but at slower speeds you also need to deal with fragmentation and the
layer 2 transport. I am surprised that there has been so little movement
as far as QoS and efficiency in regards to VoIP. Take a standard voice call
using G.726 at 32 kbps, you get 40 bytes of voice every 10 ms. Now add on
your 20 byte IP header, 8 bytes UDP, and 12 byte RTP header. So now we are
at 80 bytes and most of the time we are shoving this on ATM so our 32K
voice stream now sucks 84.8 kbps.

If you are interested in more info on QoS and Voice/Data over last mine
networks check out my website:

http://www.robotics.net/papers/integratedvoice.html


<>
Nathan Stratton                         CTO, Exario Networks, Inc.
nathan () robotics net                     nathan () exario net
http://www.robotics.net                 http://www.exario.net


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