[e2e] link between Kelly's control and TCP's AIMD

Sireen Habib Malik s.malik at tuhh.de
Tue Feb 22 02:28:22 PST 2005


I just want to continue on the comment that "(tcp) performance modelling 
have had some interesting errors". I take this as a very good chance to
understand a few things here.

Following is the most basic model (I am starting with the abc... which 
is a very nice place to start).

Area under the curve assuming periodic "packet loss" (AIMD control)

a. total_packets = (w*w)/ 4+ (w*w)/8 = 3*w*w/8
b. loss probability (p) = (1 lost packet) /(total_packets)   = 8/(3*w*w)

Therefore, w= sqrt (8/(3*p).

Since average_window = (3*w)/4, therefore,

average_window = sqrt (1.5/p).

Risking the nausea of many people here, i have included all the trivial 
steps. This very straight forward approach does lead to a non-linear 

What are the errors in this approach?

I am sure that knowing the problem with this one  will lead to a deeper 
understanding of the "Troubled" Control Protocol (excuse my twist but 
the preceding discussions do give the impression!)

Thank you for the response.

Sireen Malik
Hamburg, Gemany

Cannara wrote:

>Ooooh Ted, right through the heart!  Other papers I have read on similar TCP
>C later admitted to, but
>I promise to take some time to check the ones you suggest.
>Ted Faber wrote:
>>On Sat, Feb 19, 2005 at 12:00:23AM -0800, Cannara wrote:
>>>I don't know "ignored" -- some friends (NetPredict) have a patent on just such
>>>statistical analyses applied to TCP performance products.  It's the
>>>nonlinearity that makes any linear differential modelling grossly approximate.
>>>We have to remember some fundamentals -- at least that fluids are variously
>>>compressible & reorderable, unlike packets, and loss of molecules is not an
>>>option.  :]
>>I was going to ask if you'd even read the papers.  Thanks for answering
>>that question.
>>Ted Faber
>>http://www.isi.edu/~faber           PGP: http://www.isi.edu/~faber/pubkeys.asc
>>Unexpected attachment on this mail? See http://www.isi.edu/~faber/FAQ.html#SIG
>>  ------------------------------------------------------------------------------
>>   Part 1.2Type: application/pgp-signature


Sireen Malik, M.Sc.
PhD. Candidate,

Communication Networks
Hamburg University of  Technology,
FSP 4-06 (room 3008)
Denickestr. 17
21073 Hamburg, Deutschland

Tel: +49 (40) 42-878-3387
Fax: +49 (40) 42-878-2941
E-Mail: s.malik at tuhh.de

--Everything should be as simple as possible, but no simpler (Albert Einstein)

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