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

Jon Crowcroft Jon.Crowcroft at cl.cam.ac.uk
Fri Feb 18 00:02:35 PST 2005

so the idea of packet conservation and ack clocking was completely there in Van's original
88 paper. the continuous control theoretic model  was also pretty much there - and is partly 
from the early DEC work but i would guess that if you look at Davies work and some of the early french
packet switched net work, there was some analogy with fluids already in the back of peoples minds.

I guess the interesting thing is how much work is based on something which for a long time was pretty poor approx
(the percentage of flows that make it into a steady state being so low for ages, that the notion that each new
packet is only sent in because an ack came out was kind of fantasy land) - when Van did this mid to late 80s, the
net was full of long usenet and ftp transfers - by early 90s, it was full of tiny intsy web transfers - nowadays, i
guess we may be nearly back in the regime where  there's a reasonable percentage of longish (p2p) tcp transfers
although the ratio of access link speed to core is so huge, that from the core perspective, most tcp flows are
pretty tiny things - its only really at the inter-pop traffic that the aggregate flow might look like something
fluid approximations work for...but then it aint a TCP AIMD process, its an aggregate of a set of flows starting
and stopping which is quite a different thing...

as steven hand just said to me - 
reasoning by analogy is like trying to fix a car 
with a leaky screwdriver

In missive <20050217192035.GA77148 at pun.isi.edu>, Ted Faber typed:

 >>Content-Type: text/plain; charset=us-ascii
 >>Content-Disposition: inline
 >>On Thu, Feb 17, 2005 at 01:31:08AM +0000, Damon Wischik wrote:
 >>> Roy Xu wrote:
 >>> >I'm looking for a pointer to literatures that link the
 >>> >TCP's (discrete) AIMD to Kelly's (continuous) control formulation.
 >>> Kelly's continuous-time formulation uses a differential equation model 
 >>> (also called a fluid model) for TCP. You should look at the literature 
 >>> which describes this fluid model, starting with
 >>> "A Fluid-based Analysis of a Network of AQM Routers Supporting TCP Flows 
 >>> with an Application to RED", V. Misra, W. Gong, D. Towsley, SIGCOMM 2000.
 >>Fluid flow congestion control analysis goes beck to these guys at least:
 >>%A D. Mitra
 >>%A T. Seery
 >>%T Dynamic Adaptive Windows for High Speed Data Networks: Theory and
 >>%J Proc. SIGCOMM Symposium on Communications Architectures and Protocols
 >>%P 30-29
 >>%C Philadelphia, PA
 >>%D Sept 24-27, 1990
 >>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 
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