[e2e] Agility of RTO Estimates

[Detlef Bosau]

Hi!

Please excuse me for bothering you with this question, but I´m 
interested whether there exists material on this question.

I´m interesting in the "agility" of TCP´s retransmission timeout (RTO).

To my understanding, the RTO defines a confidence interval for a packets
RTT and therefore maintains a simple yet effective model of the path.
This model is continuously adapted by evaluation of actual ACK packets,
and immediately yields a confidence test for the zero hypothesis "packet
is successfuly delivered" with a certain, if implicit, level of
significance..  Therefore, Spurious Timeouts (refer to Ludwig, Gurtov et
al.), mathematically spoken, are errors of the first kind and thus may
occur on _any_ network, not only in wireless ones. Thus, if ST are
observed "unduly often", this may indicate that the level of confidence
has risen - in other words: RTO has not yet adapted to a larger value.

My question is, with repect to mobile wireless networks as UMTS or GPRS:
How "quickly" does RTO adapt? I expect, this is restricted by the ES-ES
latency, the packet rate (i.e. "samplin rate"), the burstiness of
traffic etc.
Can this "RTO model" follow e.g. the latency variations met on the
mobile network in "real time"?
Or are there basic limiations. (At least, I expect so.)


Many thanks!

Detlef Bosau
-- 
Detlef Bosau
Galileistrasse 30
70565 Stuttgart
Mail: detlef.bosau at web.de
Web: http://www.detlef-bosau.de
Mobile: +49 172 681 9937