Newsgroups: news.admin
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: to PEP or not to PEP?
Message-ID: <1989Aug10.175458.20369@utzoo.uucp>
Organization: U of Toronto Zoology
Date: Thu, 10 Aug 89 17:54:58 GMT

I recently sent the following to our Trailblazer-equipped neighbors, and
dialup congestion is now noticeably less common here.  It occurred to me
that others might be interested as well:

---------
[Original addressees] get news from us, and have Trailblazer links for it.
Utzoo's uucp throughput at 2400 baud these days is unfortunately not very
good; it's not much faster than 1200, probably because of Sun's scummy
ALM-1 multiplexor getting in the way.  Now, consider the following two
scenarios, which start simultaneously:

Site A tries to call utzoo with its Trailblazer.  Call fails, say because
	zoo's fast lines are busy.  So site A falls back to 2400 and calls
	zoo again.  This time the call succeeds, either because zoo does
	have a slow line free or (worse) because the fast line got
	freed up and A is now coming in at 2400 baud on a Trailblazer line.
	Effective transfer rate is now about 130 cps, so A stays on the
	line for a long time transferring news.

Site B tries to call utzoo with its Trailblazer.  Call fails, say because
	zoo's fast lines are busy.  Site B does not try to fall back; it's
	PEP or nothing for them.  They try again an hour later, and get
	through.  Effective transfer rate is maybe 1000 cps.  (I don't
	have actual numbers for this one on hand, but that's probably not
	far wrong.)

How long does it take before site B has transferred more data than site A,
despite A's one-hour head start?

About nine minutes.

Waving a magic wand and making zoo's 2400-baud connections run at ~200 cps,
the way they used to when zoo was a pdp11 [!], increases that number only
slightly.  Discounting the PEP throughput a bit, ditto.

I would suggest that unless there are factors I'm not aware of, it is in
everyone's best interests, including yours, if you do *not* fall back to
slow speeds when you can't get through to utzoo at high speed.  Trying
the high-speed call more frequently works much better.  Some of you may
already have implemented such a policy, but I know some of you haven't.
I haven't made a systematic survey, but I see some of your sites on the
slow lines with some frequency.  Worse, I see some of them on the fast
lines at low speed with some frequency, and that's hurting other sites by
tying up the Trailblazers unnecessarily.  I kill such connections when I
notice them, but they really shouldn't be initiated at all.
---------
-- 
V7 /bin/mail source: 554 lines.|     Henry Spencer at U of Toronto Zoology
1989 X.400 specs: 2200+ pages. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu