[e2e] Analytic Model of Download Time as a Function of TCP Connect Time

I am thinking of an approach to analytically determine the download time as a function of RTT given a few initial real world samples. Say, I measured a web page from 4 locations around the globe. Knowing this sample, what can I infer anything about the population of download times as a function of RTT.

If I assume that Download time (dt)can be expressed as follows:

dt = n* RTT + c

where n is the number of round trips (RTT ping pongs, includes one burst of data which can be multiple packets) with c being the server stall time between sending the data or server processing time plus some random noise all factored into once constant.

The above equation is of the form y=mx +c and I can equate the slope with that of number of round trips (makes sense as the lesser the number of round trips the lower the response time) while x is RTT.

So if I take enough sampls, say 10, and perform a regression analysis on those to generate the equation wouldnt that classify the population. If I have such an equation then I would plug in various RTT(s) and asuming the R-squared value is high wouldnt that be representative of real performance. A few initial measurements showed encouraging results but a few measurements didnt converge and a few had negative valus,etc.

Before I go further and present this to an internal audience I want to poll this group for any feedback/remarks/comments on using this method and its pitfalls.

-Paddy Ganti Received on Thu Jul 26 18:22:04 2007

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