[Tmrg] convergence time

[Andrea Baiocchi]

Dear Lachlan, dear all,
   I am following this mailing list with great interest, especially 
about raound tabel and TCP measurements/evaluation issues. Many 
thanks to Lachlan for his most appreciable initiative. I try to 
contribute.


At 13:00 -0700 27-10-2007, Lachlan Andrew wrote:
>How should we measure the responsiveness of a TCP algorithm?

can it be sensible to look at responsiveness from a point of view 
closer to the user, by measuring the time required to deliver a given 
amount of data Bklg as a function of the value of Bklg? This is a 
curve not a single value, but useful indication could be extracted 
from there (i.e. asymptotic growth rate).

>- The rise time of a single flow to an empty systems is not very
>interesting, because it many measures the impact of slow start.  Is it
>interesting to consider the response of one existing flow to one new
>flow?  An alternative is to consider time to settle when a flow
>*departs*, although that mainly measure the aggressiveness of the
>protocol, rather than its responsiveness.

My proposal above suffers from slow start dependence. It could be 
"generalized" (albeit also complicated) by considering the amount of 
time required to deliver one INCREMENT of Bklg, say DeltaB, after an 
amount Bklg0 has already been delivered. As an example, given Bklg0, 
time required to deliver further data DeltaB=alpha*Bklg0, with 
alpha=0.1. Parameters to choose for this measurement are in general 
Bklg0 and alpha. This last measurement could also be normalized to 
the overall time required to deliver Bklg0 amount of data.

for both measurements it would clerayl be key to precisely define the 
scenario (corss traffic, link/topology changes, whatever stresses 
"responsiveness" of TCP).


Thank you for you attention.
Best regards,

Andrea Baiocchi

-- 
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Andrea Baiocchi, PhD
INFOCOM Dept. - University of Roma "La Sapienza"
Via Eudossiana 18 - 00184 Roma (Italy)
E-mail: andrea.baiocchi at uniroma1.it
Phone  +39 0644585654     
Fax:     +39 064744481
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