Re: [8023-CMSG] PAR proposal
I just want to highlight the "fairness" aspect mentioned by David in his
message below.
A major benefit of doing congestion management is to allow the network
some degree of control over the sources.
To illustrate, consider a simplified situation.
Source A is trying to send 10Gbps of traffic whereas another source B of
the same priority is trying to get its 1Mbps data through the same
network. In the absence of any good congestion management mechanism,
both these sources will get drops and source B will get very little data
through.
A good set of congestion management mechanisms, on the other hand, will
try to throttle source A (as it is the congesting source), allowing
source B to get its data through. So source A will be throttled and may
see higher delays, but source B will see much lower delays and better
performance.
Taking this to an extreme, the absence of any congestion control
mechanism can cause "congestion collapse", where data is sent to the
network only to be dropped. TCP's set of congestion control mechanisms
were developed to avoid such a situation. However non-responsive flows
can still cause congestion collapse.
In summary, a good set of congestion control mechanisms do increase
latencies seen by some sources (rogue sources), but also decrease the
latencies seen by other sources (innocent sources).
Regards,
Tanmay Gupta
-----Original Message-----
From: owner-stds-802-3-cm@listserv.ieee.org
[mailto:owner-stds-802-3-cm@listserv.ieee.org] On Behalf Of David V
James
Sent: Thursday, September 23, 2004 7:07 PM
To: STDS-802-3-CM@listserv.ieee.org
Subject: Re: [8023-CMSG] PAR proposal
Brad,
I'm on your side, so please don't get upset.
I'll critique this proposal, as I suspect others will.
I'm being a devil's advocate, not the opposition.
That being said, please have patience and an open mind.
>> Ethernet is becoming the transport of choice for a broader range of
>> applications.
What new applications?
It its toasters or light switches, I doubt this is needed.
If its consumer music, then talke with the RE group.
I suspect its just server backplanes, but one can't admit
that because (some think) its not big enough to matter.
>> These applications have increased the market for improved
>> frame delivery
What does "improved frame delivery" mean? That seems rather vague.
Does it mean fewer losses?
Does it mean autonomous routing?
Does it mean no virus attacks?
Does it mean secure delivery (no eavesdropping)?
>> and latency performance.
Typical latency? Maximum latency? And how is this measured?
In general, any form of congestion management actually increases the
average latency, not decreases it.
While it may look otherwise, that just because the latency is
applied by your shapers before the frame is sent, rather than
by the queues after your frames are sent.
This is like the *****'s breakfast delay guarantee:
15 minutes or your breakfast is free. But, the timer starts after you
are seated, and does not include the time spent waiting to be
assigned a table. Sounds good in concept, but your time-till-served
probably increases, since customers are not seated until
sufficient waitress resources are available.
In general, any form of fairness or congestion management
increases (not decreases) latencies, if measured from the
application-ready time. Anytime you manage unpredictable
traffic, you stop someone from sending when they could have.
Its hard to make that up.
Not that there aren't reasons for CM. However, its more related
to low frame loss, which indirectly improves throughput by
eliminating loss-related retransmissions, thus improving
the effective bandwidths provided to the application.
>> Addition of these capabilities in an IEEE 802.3 standard will
accelerate
>> Ethernet deployment and will improve interoperability of equipment in
>> these new markets.
A little too mother and apple pie, marketing not engineering flavor.
Also, its not clear how CM improves interoperability.
Its not clear what the the new markets.
I won't be in Ottawa to complain, and I wouldn't complain if I was
there,
because I think there are some good thing to be done within the realm
of:
Classes of service
(other than being done by RE)
Only best-effort losses
However, I don't think these ideas have been well captured, and
(if not well captured) could result in rejections by others.
IMHO,
DVJ
David V. James
3180 South Ct
Palo Alto, CA 94306
Home: +1.650.494.0926
+1.650.856.9801
Cell: +1.650.954.6906
Fax: +1.360.242.5508
Base: dvj@alum.mit.edu
>> -----Original Message-----
>> From: owner-stds-802-3-cm@listserv.ieee.org
>> [mailto:owner-stds-802-3-cm@listserv.ieee.org]On Behalf Of Booth,
>> Bradley
>> Sent: Thursday, September 23, 2004 7:58 AM
>> To: STDS-802-3-CM@listserv.ieee.org
>> Subject: Re: [8023-CMSG] PAR proposal
>>
>>
>> Ben,
>>
>> I like the changes in the last slide, but I think I'd re-word the two
>> points in that slide as follows:
>> Ethernet is becoming the transport of choice for a broader range of
>> applications. These applications have increased the market for
improved
>> frame delivery and latency performance.
>> Addition of these capabilities in an IEEE 802.3 standard will
accelerate
>> Ethernet deployment and will improve interoperability of equipment in
>> these new markets.
>>
>> Thoughts?
>>
>> Thanks,
>> Brad
>>
>> -----Original Message-----
>> From: owner-stds-802-3-cm@listserv.ieee.org
>> [mailto:owner-stds-802-3-cm@listserv.ieee.org] On Behalf Of Benjamin
>> Brown
>> Sent: Thursday, September 23, 2004 7:36 AM
>> To: STDS-802-3-CM@listserv.ieee.org
>> Subject: Re: [8023-CMSG] PAR proposal
>>
>>
>> Brad, Gadi, Matt, Asif,
>>
>> Thanks for your review. I've captured Brad's suggested changes
>> in the first 4 slides of the new attached proposal. I then added a
>> 5th slide which is a markup of the 4th with my changes in response
>> to some of Matt's comments. If everyone could take another look
>> at this and let me know what they think of the new document, the
>> proposed changes or anything else they can think of, I'd very much
>> appreciate it.
>>
>> Regards,
>> Ben
>>
>> Booth, Bradley wrote:
>>
>> >Ben and all,
>> >
>> >Some feedback on this.
>> >
>> >Cheers,
>> >Brad
>> >
>> >-----Original Message-----
>> >From: owner-stds-802-3-cm@listserv.ieee.org
>> >[mailto:owner-stds-802-3-cm@listserv.ieee.org] On Behalf Of Benjamin
>> >Brown
>> >Sent: Wednesday, September 22, 2004 4:03 AM
>> >To: STDS-802-3-CM@listserv.ieee.org
>> >Subject: [8023-CMSG] PAR proposal
>> >
>> >
>> >All,
>> >
>> >This is not a full cut at the PAR but covers the more interesting
>> >pieces - Title, Scope, and Purpose. Please review and comment.
>> >Again, this, or something similar, needs to be approved in Ottawa
>> >next week in order to pre-circulate for approval at the WG level
>> >in San Antonio in November. Please give this serious attention
>> >and comment with actual suggested changes.
>> >
>> >Thanks,
>> >Ben
>> >
>> >--
>> >-----------------------------------------
>> >Benjamin Brown
>> >178 Bear Hill Road
>> >Chichester, NH 03258
>> >603-491-0296 - Cell
>> >603-798-4115 - Office
>> >benjamin-dot-brown-at-ieee-dot-org
>> >(Will this cut down on my spam???)
>> >-----------------------------------------
>> >
>> >
>> >
>>
>> --
>> -----------------------------------------
>> Benjamin Brown
>> 178 Bear Hill Road
>> Chichester, NH 03258
>> 603-491-0296 - Cell
>> 603-798-4115 - Office
>> benjamin-dot-brown-at-ieee-dot-org
>> (Will this cut down on my spam???)
>> -----------------------------------------
>>