Subject: [ledbat] pointer to Lars' work on packet preemption issues in backgrounding

From: Joe Touch <[email-masked]>
Date: Thu, 20 Nov 2008 12:21:53 -0800

Hi, all,

FYI, here's a pointer to the issue I was raising at the mic, that
routers don't preempt packets as they're going out the door (nor do
hosts; Bob Briscoe noted that there were modems that do this, though).

Idletime Scheduling with Preemption Intervals. Lars Eggert and Joe
Touch. Proc. 20th ACM Symposium on Operating Systems Principles (SOSP
2005), Brighton, United Kingdom, October 23-26, 2005, pp. 249-262.
http://people.nokia.net/~lars/papers/f109-eggert.pdf

Disclaimer: This was Lars' thesis work, and I was his advisor. It's of
'academic' interest IMO that it represents the floor of the best you can
expect to reduce the impact of background traffic on foreground without
'extraordinary means' like either his thesis technique or true preemption.

Joe
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From: Carsten Bormann <[email-masked]>
Date: Thu, 20 Nov 2008 14:49:55 -0600

On Nov 20, 2008, at 14:21 , Joe Touch wrote:

> routers don't preempt packets

RFC 2686

http://www.cisco.com/en/US/docs/ios/12_2t/12_2t13/feature/guide/ftmmlppp.html

Of course, this is irrelevant in the home.
(Just wanted to fix the overgeneralization.)

Gruesse, Carsten

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From: Joe Touch <[email-masked]>
Date: Thu, 20 Nov 2008 12:53:12 -0800

> (Just wanted to fix the overgeneralization.)

Thanks - Dave pointed that out to me as well. I was not aware of it;
it's certainly still reasonable that "most routers" don't support
preemption.

Ditto for hosts.

Joe