[e2e] Is a control theoretic approach sound?

Panos GEVROS panos.gevros at cl.cam.ac.uk
Wed Jul 30 16:14:35 PDT 2003

----- 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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