[e2e] Is a control theoretic approach sound?
ggumdol at comis.kaist.ac.kr
Thu Jul 31 07:31:18 PDT 2003
I think the paper "A Unifying Passivity Approach for Network Flow Control" in IEEE Infocom2003 by John Wen and Murat Arcak is one of the best papers published in this area up to now although the concepts exploited in this paper is not easy. It's only my opinion.
One drawback of this paper is that the paper does not consider time delay in their main analysis, but proves local stability through linearization about the equilibrium point. (In fact, proving global stability might be very hard in nonlinear control system.)
Although we cannot know whether these kinds of approach will be used in real networks, they provide us invaluable insights into the network in flow level.
Ph.D Candidate in Network Systems Lab., Dept. of EECS,
Korea Advanced Institute of Science and Technology
373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, Republic of Korea
E-mail: ggumdol at netsys.kaist.ac.kr
----- Original Message -----
From: "Shivkumar Kalyanaraman" <shivkuma at ecse.rpi.edu>
To: <end2end-interest at postel.org>
Cc: "John Wen" <wen at ecse.rpi.edu>; "Murat Arcak" <arcak at ecse.rpi.edu>
Sent: Thursday, July 31, 2003 9:49 AM
Subject: Re: [e2e] Is a control theoretic approach sound?
> The issue of considering delay robustness and several other
> properties directly in a non-linear dynamic control theoretic framework
> has been proposed by my control-theory colleagues John Wen and Murat Arcak
> in their INFOCOM 2003 paper -- this framework is a superset of Kelly and
> Low static optimization frameworks and linearized stability analyses.
> Since my colleagues do not read this mailing list, please cc your
> responses directly to them too.
> It is becoming clear that basic dynamics and steady state behavior of
> congestion control schemes are best understood at the "flow"
> level in optimization frameworks; and "fine-tuning" of schemes can be done
> at the "packet" level (eg: estimation robustness issues,
> increase/decrease: AIMD etc, slow start, interaction with timeout/rtt
> estimation etc). This "packet-level" dynamic behavior can be validated by
> ns-2 simulations or implementation trials.
> This is the essence of the approach of Kelly and Low frameworks and the
> other generalized frameworks...
> Shivkumar Kalyanaraman
> Associate Professor, Dept of ECSE, Rensselaer Polytechnic Institute (RPI)
> 110, 8th Street, Room JEC 6003, Troy NY 12180-3590
> Ph: 518 276 8979 Fax: 518 276 4403
> WWW: http://www.ecse.rpi.edu/Homepages/shivkuma
> A goal is a dream with a deadline -C. Knight
> On Thu, 31 Jul 2003, Panos GEVROS wrote:
> > ----- Original Message -----
> > From: "Yunhong Gu" <ygu1 at cs.uic.edu>
> > Subject: Re: [e2e] Is a control theoretic approach sound?
> > > Well, I think to decide how "aggressive" the AI will be is not that
> > > *simple* a problem :) It is not the more aggressive the better (even if
> > > the per flow throughput is the only objective), right?
> > agreed but only if you want to address the problem in its full generality
> > ... if it is restricted to those areas of the (capacity,traffic) space where
> > the packet loss is in [0...7-8%] range (and AIMD is indeed relevant) since
> > out of this range timeouts start becoming the norm) then it is
> > *fairly*straightforward* to decide on AIMD parameters which provide specific
> > outcomes (wrt individual connection perfromance -within limits obviously-
> > and wrt capacity utilisation).
> > > > ..in their case they know pretty much that the links they are using are
> > in the
> > > > gigabit range and there are not many others using these links at the
> > same time.
> > > >
> > >
> > > But what if there are loss, especially continuous loss during the bulk
> > > data transfer? No matter how large the cwnd is initially, it can decrease
> > > to 1 during the transfer, then the problem arise again.
> > drastic measures (timeout, exponential backoff etc) will always need to be
> > in place -
> > I 'm saying that (at least in the first attempt) it pays being optimistic
> > (this is the idea underlying slow start anyway..)- and in certain
> > environments indeed more optimistic than the standard prescribes since there
> > is a-priori knowledge of the network path characteristics and even traffic
> > conditions - which is the case when considering OCxx links connecting
> > particle physics laboratories.
> > this approach seems to me a lot simpler and (most likely) equally effective
> > compared to elaborate control schemes which try to do better while trying
> > hard to remain "friendly" at the same time.
> > Panos
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