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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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