Subject: [Diffserv] On RED in a Diffserv MIB

From: Kathleen Nichols <[email-masked]>
Date: Thu, 06 Apr 2000 12:05:40 -0700

This note is most definitely with my WG co-chair hat OFF and Brian will
probably ding me for rambling on about a non-DS topic. I do have 
concerns that a detailed discussion of RED is NOT a DS topic. However,
the MIB discussion keeps pulling it in and I have been asked to post
my individual thinking on the topic. I still believe that much of
this is not relevant to the Diffserv MIB, but with many reservations,
I will weigh in (and without consulting my collaborators).

My context is that I've been working with Van Jacobson and Kedar Poduri
on "rethinking" RED since late 1997. (More recently, Li Fan has been
involved in the RED work.) We did some internal Bay reports on early
work and Van used some of this in an early 98 email exchange with Sean
Doran on parameter-setting for the 93RED. I believe that Van's
suggestions
worked out, but you'd have to talk to Sean. We had started to develop
a different control law for RED as well as several other changes
and work on why we did this. Van gave a talk at the June 98 Nanog
(which I assume is still available in their archives) on the development
of a new control law and why and how to think of RED as a controller
which is somewhat key to understanding where we're coming from. 

We have a draft paper that's been pretty much in the same form since
January of 99 (embarassingly enough) that quite a number of people
have seen and is semi-public, but I won't post the URL until Van
is ready. Although the development and much of the "how to" is
rather different from the 93 RED work, I believe the same set of
parameters could be used, though they would be set to different
values and used a bit differently. Namely, a "filter gain" or
"queue weight", a "min_thresh" or just "threshold" for the
control region, and a "max_thresh" or range of the control region.
This seems to cover most of the known flavors of RED and seems
reasonable for a MIB. I don't think it makes sense to specify
the algorithm via a MIB since I don't think a box will let you
choose. It may make sense to *report* what algorithm that box
uses, but having been at two companies that make boxes, I can
say that there are many flavors of flavors when engineers get
down to implementing, so I don't know how useful or accurate
that can be. (This paragraph is the one that is relevant to
the MIB discussion.)

The work that Kwok referenced from Firiou and Borden appears
to borrow from our work in some of its early sections,
specifically Van's control law discussions and my math on
the step response (Victor and Marty had seen our draft,
of course, as colleague and boss of Kedar), but as that
paper uses one of those "mythical Internet" simulations
of a few long-lived TCPs of the same known RTTs, they
reached erroneous conclusions about useful parameters. This
is what Van meant when he said in the DS WG that if you
used those parameters, you'd be in trouble. (You know how
everyone says to add "multicast" to some problem to make
it a lot harder? When it comes to analyzing how something
works with network traffic, I say add HTTP and varied
RTTs to make it a lot harder. But then it would take too
long for the people who want to turn out papers.) We felt,
as active researchers in this area, some duty to say "don't
do it!" when Kwok recommended that paper and those settings
of the traditional parameters.

For full disclosure, I should say that our draft paper was
rejected by Sigcomm 99. A major complaint was that it was
too long and unfinished (that's Van's fault!) and that we
didn't understand the 93 RED paper (so I guess we share that).
Thus, you can take my thoughts on this subject with a grain
of salt if you are so inclined.

On the other hand, our "RED in a different light" (or RED-light) 
work has been presented/discussed with folks at Torrent, Bay 
(pre-NortelNetworks), Argon, and Cisco. I don't know what, if
anything, the former three have done with it. A variety of things
are going on at Cisco. One of these is that Fred Baker did an
implementation of it in something like Fall of 98 and I believe
he's gotten good results with it, but I won't speak for Fred. At
Cisco, we've done work on RED-light for high bandwidth links,
multiple queues, and a couple of other things that perhaps should
not be said publically yet. It seems promising. All it needs
for setting is the three parameters (in fact, we could probably
have them all derived from one parameter, but then that would
exclude other RED implementations). I also want to note that
we simulate with a much wider range of traffic conditions than
I've seen discussed anywhere.

	Kathie

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From: Brian E Carpenter <[email-masked]>
Date: Thu, 06 Apr 2000 16:09:52 -0500

Wow! A chance to keep my co-chair in check!

While the details of RED control laws are rather out of scope, there
is an important point for the diffserv MIB here: it's obvious that as 
long as there is theoretical debate about the form of the law,
carving a RED control law in stone in the MIB would be a mistake. 
So, Andrew, please consider that in revising the MIB . (I'm hoping 
the PIB will avoid that level of detail, but if it can't, obviously
the same applies.)

I guess the RED details are better discussed on e2e-interest or
somwhere like that.

   Brian

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From: Fred Baker <[email-masked]>
Date: Thu, 06 Apr 2000 18:31:14 -0400

At 12:05 PM 4/6/00 -0700, Kathleen Nichols wrote:
>One of these is that Fred Baker did an
>he's gotten good results with it, but I won't speak for Fred.

Yes, much better results than I got with RED-93

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From: "Victor Firoiu" <[email-masked]>
Date: Fri, 07 Apr 2000 11:27:47 -0400

Dear diffserv-ers,

we apologize for abusing this list with an out-of-scope message, but
we feel obligated to respond to a recent message that has a work of
ours as a direct target.

First, we strongly reject all allegations of borrowing of any kind.
Our paper: 

"A study of active queue management for congestion control"
by Victor Firoiu and Marty Borden, published in Infocom 2000, 
http://www.ieee-infocom.org/2000/papers/405.pdf

is based only on the widely accepted model for TCP throughput:

"Modeling TCP throughput: a simple model and its empirical validation"
by J.Padhye,V.Firoiu,D.Towsley, J.Kurose, published in Sigcomm 1998.
http://www.acm.org/sigcomm/sigcomm98/tp/abs_25.html

and on our extensive experiments both simulated and implemented.

Our results relevant to the DS MIB discussion have been reinforced and
confirmed by many other contributions including:

Floyd, S., Recommendation on using the "gentle_" variant of RED
http://www.aciri.org/floyd/red/gentle.html

V. Rosolen, Bonaventure, O., and G. Leduc, A RED discard strategy for
ATM networks and its performance evaluation with TCP/IP traffic, ACM
Computer Communication Review, July 1999,
http://www.info.fundp.ac.be/~obo/biblio.html
Impact of cell discard strategies on TCP/IP in ATM UBR networks,
Proc. of the 6th Workshop on Performance Modelling and Evaluation of
ATM Networks (IFIP ATM'98) Ilkley, UK, July 98.
http://www-run.montefiore.ulg.ac.be/publications/papers/abstract-PP98-02.html

Analytic Evaluation of RED Performance Martin May (INRIA), Thomas
Bonald (INRIA), Jean Bolot(ENSIM)
http://www.ieee-infocom.org/2000/papers/369.ps

Regarding the technical merits of different studies and architectures
for queue management, we are open for discussions.  Probably a good
place is the end2end-interest mail list, where we have submitted and
discussed our above works.

Sincerely yours
--
Victor Firoiu and Marty Borden