Re: [RPRWG] Merits of Open Loop
Adisak,
Please see my reply below.
Regards, Siamack
Adisak Mekkittikul wrote:
> Siamack,Some of what you mentioned in the slides are quite
> inaccurate, may be implementation specific.
> > Adisak, it would help if you were more specific. Please point
> out the inaccuracies so that we can all see and move on.
>
> The fact is, CA applies to all priorities of traffic.
> > Interesting reversal of position since last time we talked you
> mentioned that high priority traffic is only a small portion of the
> ring traffic and the CA does not apply to it. I guess that's why we
> are having these discussions so that a common understanding would
> emerge. Perhaps you should revise your Portland presentation and
> clearly show that ring bandwidth is partitioned dynamically and that
> high priority access does wait for low priority transit to get
> through.
>
>
> However, one can choose to implement their transit path, line card
> differently. For example, we decide to one implement for our line card
> so that we canachieve sub-millisecond jiiter for circuit emulation
> traffic.
> > Wonderful, however so far we only have your word for it. Where
> was this documented and how does it impact the 802.17 discussion we
> are having.
> Please revisit my simulation presentations again, you might have
> missed some detail. The lastthing we want to do for the working group
> is getting bogged down on a non-quantitative performance speculation.
>
> > Adisak, 802.17 is an open forum. I welcome your specific
> technical comments on the presentation's content.
> Adisak
>
> -----Original Message-----
> From: Siamack Ayandeh [mailto:sayandeh@xxxxxxxxxx]
> Sent: Tuesday, August 07, 2001 10:58 AM
> To: Harmen van As
> Cc: stds-802-17@xxxxxxxx
> Subject: Re: [RPRWG] Merits of Open Loop
>
> Harmen,
>
> Please see my comments below. Thanks for the interest.
>
> Regards, Siamack
>
> Harmen van As wrote:
>
> > Dear SiamackIt would be necessary to back off your
> > statements on the merits andperformance of Open Loop with
> > simulations.
> >
> > > My statements are based on the protocol flow charts &
> > simulation of congestion avoidance algorithms conducted so
> > far. Please see slide #5 for the list of references.
> >
> > The goal of MAC protocolsis also to achieve fairness among
> > iinterfering nodes, not merely congestioncontrol.
> >
> > > It would be helpful to have a concise description of
> > this goal, what is fairness in this context, and what
> > interference you have in mind. I have shown that CA
> > algorithms covered can introduce HOL blocking which is a
> > form of interference. Open loop congestion controls do not
> > do this.
>
> >
> > The first two statements on CA mechanisms is certainly
> > not true at all.
> >
> > > Again the references in slide #5, & existing simulations
> > show that the weighted fairness algorithms are only
> > targetting the low priority class i.e. C' portion of the
> > ring bandwidth (C'= C-a ). This is what I call static
> > partitioning.
> >
> > >The delay bound that I have in mind is due to the high
> > priority traffic class only. i.e. the ring access delay of
> > the high priority traffic is only due to high priority
> > traffic on the ring. In some CA schemes and under certain
> > conditions described in the slides, the low priority
> > traffic is interfering with this bound. i.e. low priority
> > ring traffic is scheduled ahead of high priority acess.
> >
> > >Of course if one is patient enough even best effort
> > traffic would eventullay make it through. So we have to
> > be careful that we are on the same page with respect to
> > delay bounds.
> > We will show that by two protocols having different
> > degrees of sophistication.Seems to become an interesting
> > and lively September meeting in San Jose.
> >
> > > Looking forward to it.
>
> > Best
> > regardsHarmen------------------------------------------------------------------
> >
> > Prof.Dr. Harmen R. van As Institute of Communication
> > Networks
> > Head of Institute Vienna University
> > of Technology
> > Tel +43-1-58801-38800 Favoritenstrasse 9/388
> > Fax +43-1-58801-38898 A-1040 Vienna, Austria
> > http://www.ikn.tuwien.ac.at email:
> > Harmen.R.van-As@xxxxxxxxxxxx
> >
> > -----------------------------------------------------------------ORIGINAL
> > MESSAGETo: stds-802-17@xxxxxxxx
> > Subject: [RPRWG] Merits of Open Loop
> > From: Siamack Ayandeh <sayandeh@xxxxxxxxxx>
> > Date: Mon, 06 Aug 2001 11:01:39 -0400
> > CC: sayandeh@xxxxxxxxxx
> > Sender: owner-stds-802-17@xxxxxxxxxxxxxxxxxx
> > Folks, As some people are busy doing simulations and
> > writing proposals for the
> > San Jose meeting, I am posting this presentation early on
> > the
> > reflector. It describes the merits of open loop
> > congestion controls and
> > may impact some of the simulation scenarios that would be
> > presented.
> > The main conclusions of the document are that: -
> > Congestion avoidance algorithms may lead to static
> > partitioning of the
> > ring bandwidth between high and low priority traffic
> > - With CA it may not be possible to bound the ring access
> > delay of high
> > priority traffic
> > - Open loop does not suffer from HOL blocking
> > - Open loop has relatively low configuration and
> > operational complexity
> > - Open loop is not prone to tuning issues, or link
> > aggregation, etc... Regards, Siamack
>
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