[e2e] Is a control theoretic approach sound?

[Saverio Mascolo]

Hi,

why do you think that TCP is a nonlinear system?

By quoting V. Jacobson cornerstone paper :

"Network is, to a a very good approximation, a linear system. That is, it is
composed of elements that behave like linear operator-integrators, delays,
gain stages, etc"
- Van Jacobson, "Congestion Avoidance and Control," in Proceedings of ACM
Sigcomm'88.

I think that modeling the TCP as a nonlinear system not only introduces not
useful complexity but it is  wrong!

Saverio Mascolo



----- 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 2:49 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...
>
> -Shiv
> ===
> 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
> >
> >
> >
> >
> >
> >
> >
>