[e2e] Is a control theoretic approach sound?
shivkuma at ecse.rpi.edu
Wed Jul 30 17:49:55 PDT 2003
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...
Associate Professor, Dept of ECSE, Rensselaer Polytechnic Institute (RPI)
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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.
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