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Re: [8023-CMTF] 802.3ar/D0.9 is available



We've had this discussion in the past and it gets ignored or over ridden at the next meeting, but I'll put it forward one last time.  What we've proposed for #1 below is either too little to be useful and would violate #3 if it were modified to actually perform a useful funciton.

The current proposal performs static rate limiting at layer 2 by throttling the IPG to reduce all traffic being transmitted from the MAC based on an undefined congestion signaling mechanism.

A computer connects to a network, which means it communicates with more than one device up stream. If the WAN device throttles my 1GB Ethernet MAC back to 500K I'd be rather disappointed with performance on connections to my printer, and media center. Unfortunately, as simple and benign as this proposal seems, in reality, static rate limiting is only useful if it is done on a, per connection or per session basis. Any given layer 2 connection has many of these. In fact the problem is that the number is un-bounded.

Since Layer 3 is where connections, and sessions are established, the only logical place for a static rate limiting mechanism to exist is above layer 3, NOT IN THE MAC! Unless of course you want to violate objective #3 below.  Need I remind us all that the ATM guys tried this and lost to Ethernet when it came to cost, complexity and scalability.

The problem is that there are folks with diverse needs who want to have a congestion management funciton over Ethernet. One, all encompasing  layer 2 solution won't fit all of their needs. What we could be doing, is defining some primitive MAC layer functions that would facilitate a variety of fabric management solutions that could be implemented on top of Ethernet. If we bother to look at the needs of those who've come to meetings in the past, it would be obvious that they need session/connection level rate limiting and we simply can't do this at layer 2 in Ethernet without it becoming something more like ATM, PCI-Express, etc..

I'd propose that we discuss how the MAC can help with the following:

1. Supporting in band congestion signaling ( pushing congestion messages to the head of queue)
2. Link utilization threshold alarms

There's complexity in what I've just proposed above as well.  The MAC layer at best, can only expect to communicate primitive status to a higher layer management agent. We need to keep any mechanism we propose simple, such that it doesn't add to cost, complexity or latency. This can be done, but not without involving (or God forbid even embracing) other standards out of the purview of the IEEE, and there in lies our problem.

If we want to blissfully believe that throtting all traffic from a MAC layer solves our problem,  we can claim success and move forward, in spite of the fact that we have no idea what the actual mechanism is that will be controling this feature. On the other hand are we truly putting the necessary rigor into this standard by doing so?


-m.hathaway

Kevin Daines wrote:
David,
 
Not sure what you mean by "primary objective". Perhaps you didn't intend to use the "reserved word" objective. The following are the (4) TF objectives:
 
1) Specify a mechanism to limit the rate of transmitted data on an Ethernet link
2)
Specify a mechanism to support the communication of congestion information
3) Preserve the MAC/PLS service interfaces
4) Minimize throughput reduction in non-congested flows
 
The CMTF adopted a proposal to satisfy CMTF objective #1.
 
Recently, proposals related to (backward) congestion notification have been made in 802.1 (related to #2).
 
 
 
Kevin Daines
Chair, P802.3ar TF


From: David V James [mailto:dvj@alum.mit.edu]
Sent: Tuesday, October 25, 2005 11:04 PM
To: Kevin Daines; STDS-802-3-CM@listserv.ieee.org
Subject: RE: [8023-CMTF] 802.3ar/D0.9 is available

Kevin,
 
I would claim that the TF has still not provided any promising
solutions for avoiding dropped frames in a short-distance
(computer room) environment.
 
Thus, since it doesn't currently meet its primary objective,
I would smile (rather than frown) at radical new ideas that
have a chance of meeting the primary objective.
 
DVJ

 
-----Original Message-----
From: Kevin Daines [mailto:Kevin.Daines@WWP.COM]
Sent: Tuesday, October 25, 2005 5:20 PM
To: STDS-802-3-CM@listserv.ieee.org
Subject: Re: [8023-CMTF] 802.3ar/D0.9 is available

Asif,
 
As with any TF meeting pre-D1.0, presentations in support of or related to the TF objectives are welcome and encouraged. Post-D1.0, the TF naturally shifts its focus to perfecting the draft. During that phase, radically new ideas are generally frowned upon.
 
That said, the plans for the meeting are
 
1) Review D0.9 and prepare D1.0. Since we have adopted one proposal in support of one of our objectives, it is the first order of business.
2) Entertain presentations, if any, in support of or related to the TF objectives.  I'll send my customary "Call for presentations" e-mail shortly.
 
Kevin Daines
Chair, P802.3ar TF


From: Asif Hazarika [mailto:ahazarik@FMA.FUJITSU.COM]
Sent: Tuesday, October 25, 2005 5:10 PM
To: STDS-802-3-CM@listserv.ieee.org
Subject: Re: [8023-CMTF] 802.3ar/D0.9 is available

Kevin,
 
Hello. Time to discuss about the plans for the  plenary meeting.
What are the plans? We would like to meet and discuss the draft and get updates.
 
regards
asif
 
-----Original Message-----
From: Kevin Daines [mailto:Kevin.Daines@WWP.COM]
Sent: Tuesday, October 25, 2005 3:51 PM
To: STDS-802-3-CM@listserv.ieee.org
Subject: [8023-CMTF] 802.3ar/D0.9 is available

Congestion Management TF members,
 
At the July 2005 IEEE 802 Plenary meeting in San Francisco, we (the P802.3ar CMTF) passed the following motion:
 
"Adopt changes to Clause 4, Annex 4A & Clause 30 described in barrass_1_0505.pdf as a baseline proposal for 802.3ar/D1.0. The changes to Clause 4 will be made after the
changes to Annex 4A have been solidified in 802.3ar TF review."
 
In order to jumpstart our progress on D1.0, Hugh Barrass and I have prepared P802.3ar/D0.9 for CMTF preview. It may be found here:
 
 
Please note this draft has no official status. It is being made available for TF preview, prior to the November meeting, in order to more efficiently prepare P802.3ar/D1.0 and commence TF ballot after we meet in November. Hope to see you in Vancouver.
 
 
Kevin Daines
Chair, P802.3ar CMTF
 
 

-- 
Michael Hathaway
Pico Innovations
Voice: 512-327-9563
Fax: 877-408-0059
Email: mhathaway@picoinnovations.com