As long as the resulting traffic is
compliant with it's bandwidth reservation, i.e. it doesn't send more packets
per shaping period than reserved, it shouldn't produce any additional latency.
Having said that: If CBR traffic hicks
up and then tries to catch-up with the streaming rate, it would violate
its bandwidth allocation and indeed would produce additional latency. Is
this what you mean by hick up? I assume in my calculation that this does
"James, David V"
11/03/2005 03:02 PM
Maksim Azarov/SMSC@SMSC, <STDS-802-3-RE@listserv.ieee.org>
RE: [RE] Comparing graphical analysis
From a worst-case perspective,
CBR traffic with a hickup at the wrong time
(traffic stops momentarily) gives much worse latency numbers.
Have you thought about how this
could be included in your model?
Its at first counter-intuitive:
transients that reduce the loading actually
can make the worst case latencies
If this effect could be included
in your model, then I would feel more
confident that we are addressing
the true "worst case" bandwidths.
From: Max Azarov [mailto:Max.Azarov@SMSC.COM]
Sent: Thursday, November 03, 2005 10:15 AM
Subject: [RE] Comparing graphical analysis and analytical
I've looked through the David's charts and figures in the effort to synchronize
our results on the worst-case latency figures. Few observations:
1) Graphical analysis is considering both input-queue and output-queue
routers. My work exclusively deals with the output-queue routers.
2) In graphical analysis of traffic patterns I couldn't find an explicit
value for bandwidth shaping period under consideration. This definitely
has an effect on the outcome. For the 3 port output queue analysis it seemed
that 125 mks shaping period was used.
3) For the output-port router graphical analysis for 3 ports, figures are
actually in a very good agreement with the analytical formula for the shaping
period of 125 mks and 75% link utilization. In fact when I graphed latency
values from the David's paper they where almost linear and also fit tightly
with the graphs produced analytically. On the attached graph, analytical
curve is black, while curve from the values in the Dave's paper (http://grouper.ieee.org/groups/802/3/re_study/public/200509/dvjBurstAndBunch2005Sep26.pdf,
table F.3 on the page 10) is blue.
All this leads me to believe that there no drastic disagreement in results