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

Vishal Misra misra at cs.columbia.edu
Sat Feb 19 05:17:59 PST 2005

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.  :]

"fluid" modeling doesn't imply an application of Hydraulics or 
Bernoulloi's laws for protocol analysis. The "fluid" simply 
implies that the quantity that is being analyzed is continuous, 
and not discrete. Fluid models of TCP themselves come in two flavors
	- one that analyze some mean value, and hence are intrinsically 
continuous in nature (e.g., the Sigcomm 2000 paper mentioned 
earlier in the thread), and,
	- the other kind where the "fluid limit" or continuous property 
is obtained from a scaling of some parameters to infinity, e.g., 
the number of flows (the Performance 2002 paper mentioned in the 
same posting).

The differential equations that are obtained are non-linear, 
simply being "fluid" does not constrain them to linearity. 
Additionally, stochastic differential equation based "fluid" 
models of TCP allow jump discontinuities.


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