[e2e] Estimating MS windows RTO equation

Detlef Bosau detlef.bosau at web.de
Thu Feb 2 12:53:09 PST 2006

francesco at net.infocom.uniroma1.it wrote:
> Our results cannot be considered as general but refer to the monitored UMTS/GPRS
> network. It would be interesting to see other results from different
> networks...

This would be interesting in fact. However, as I already wrote to Thomas
Ziegler as a PM, I would hardly expect similar results there.

It would be particularly interesting to change the wireless/mobility
conditions with those experiments. I think, the applications
will not really matter. The interesting question is: Will a change in
the wireless condition result in "delay spikes" or abrupt delay 
changes that can cause spurious timeouts? I don´t really expect this.
When I want to produce SRTO in simulations, I must
introduce extremely hard and abrupt latency changes into the path. And
even if the BER of a wireless channel (refer to
suffers from abrupt changes, causing abrubt changes in the BLER, one
single TCP or UDP packet usually consists of serveral
"radio blocks", thus the transport latency for a whole UDP or TCP packet
is the sum from a number of, roughly spoken, geometrically distributed
random numbers. In consequence, even an abrupt change in the wireless
condition does not result in an abrubt change in the transport latencies
but only the expectian and variation of this latency changes. The
latencies themselves are still "sufficiently smooth" so that 
a sender´s rxmittimer can "follow" them or, in case of large variation,
is sufficiently large.

That´s what I conclude from my "home made" model - and your observations
confirm this.

Basically, the "big picture" of this is an old question of mine: 
"Adverse interactions between L4 and L2, are they myth or reality?"

I know there is quite a lot of work around concerning this topic. But I
must admit: I´m absolutely not convinced of this.
As I have written to Thomas Ziegler, I´m still not convinced that there
at least _exist_ any particular interactions between
mobile wireless networks and TCP which require structural changes to

If you asked me for this a year ago, I would have given a completely
different answer. But as you wrote in your paper,
it is at least questionable that TCP must be changed in order to be used
with wireless networks.


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

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