[e2e] Spurious Timeouts in mobile wireless networks, was: Re: Retransmission Timouts revisited

Wesley Eddy weddy at grc.nasa.gov
Thu Sep 1 07:30:37 PDT 2005

On Thu, Sep 01, 2005 at 03:58:06PM +0200, Francesco Vacirca wrote:
> Spurious timeouts are a second (marginal) problem that in my opinion 
> (and in my research) are not frequent events in a well engineered 
> GPRS/UMTS network.

Just curious ... Does this definition of "well-designed" include those
networks run by major service providers?  I've witnessed a few timeouts
due not to loss in the data path, but delay of either data or acks (TCP
Timestamp or DSACK options make it clear that loss is not the problem),
over one provider's North American CDMA 2000 network.  I presume that
those delay spikes were contributed to by exactly the ARQ persistence
you advocate, among other factors.  In my (subjective) real world
experience, data loss on this particular network is pretty rare, and
timeouts are common enough that you see 3 or 4 of them doing normal
things like web-surfing, fetchmail, and ssh over the course of an hour.
I use such a link frequently and have several traces and other
measurements (circa Spring 2004) that support this.


Wesley M. Eddy
Verizon FNS / NASA GRC
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