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RE: [RPRWG] Merits of Open Loop



Siamack,
 
Some of what you mentioned in the slides are quite inaccurate, may be implementation specific.
 
The fact is, CA applies to all priorities of traffic. 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 can
achieve sub-millisecond jiiter for circuit emulation traffic.
 
Please revisit my simulation presentations again, you might have missed some detail. The last
thing we want to do for the working group is getting bogged down on a non-quantitative
performance speculation. 
 
 
 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