[e2e] Agility of RTO Estimates, stability, vulneratibilites

[Christian Huitema]

I think we should just look at a simple question. Does the current
algorithm actually works? 

I personally did measurements 6 years ago. The measurement of
tcp-connect times to various web servers clearly showed a power law
distribution. There is in fact a history of finding power laws in
measurement of communication systems. In fact, Mandelbrot work on
fractals started with an analysis of the distribution of errors on a
modem link! Based on all that, it is quite reasonable to assume that the
distribution of RTT measurement follows a power law. 

People will immediately mention that it should be a truncated power law,
but even that is far from clear. There is at least anecdotal evidence of
packets being held up in queues and then transmitted after a very long
time, e.g. half an hour...

The current RTT estimators are based on exponential averages of
consecutive samples of delays and variations. This is an issue, as the
exponential average of a heavy tailed distribution also is a heavy
tailed distribution. If you plug that in a simulation, you will observe
that the estimates behave erratically. 

My personal feeling is that the current RTT estimators do not actually
work.

-- Christian Huitema