[e2e] Agility of RTO Estimates, stability, vulneratibilites

[Craig Partridge]

In message <42E35AA7.60301 at web.de>, Detlef Bosau writes:

>Craig wrote:
>
>>> I believe the immediate issue is not the "RTO model" but rather the
>>> question of what RTO estimator you use.  In the late 1980s there was
>>> a crisis of confidence in RTO estimators -- a problem we dealt with by
>
>What´s the meaning of confidence here?

I wrote in the non-mathematical sense -- if you read Lixia Zhang's "Why
TCP Timers Don't Work" or Raj Jain's paper on the failings of all
known methods of RTT estimation at the time, you'll see there was
a view that said, perhaps, it wasn't possible to measure RTT correctly.

>So, at least _one_ assumption for a network is inevitable in order to 
>use sender initiated, timeout based retransmission: Convergent 
>estimators for the timeout must exist.
>
>Unfortunaly, a priori we do not know about possible limitaions of RTT, 
>particularly there is no general upper limit. So it is somewhat 
>cumbersome to derive an 1-alpha confidence interval directly from the 
>sample here. In fact, it is a common approach in statistics, to derive 
>confidence intervals from estimates for expectation and variation of a 
>stochastic variable. Often there is some implicit assumption about the 
>districution function of this varible, e.g. gaussian.

Right -- we do not know the distribution function for the RTT.  The
key issue (and the one that Zhang and Jain raised) is that periodically
the path changes such that the RTT changes wildly.

More in following note.

Craig