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From: rpw3@redwood.UUCP (Rob Warnock)
Newsgroups: net.news,net.dcom
Subject: Re: 2400 baud modems and uucp inefficiencies
Message-ID: <54@redwood.UUCP>
Date: Tue, 2-Oct-84 18:25:40 EDT
Article-I.D.: redwood.54
Posted: Tue Oct  2 18:25:40 1984
Date-Received: Wed, 3-Oct-84 07:14:17 EDT
References: <184@oliveb.UUCP>
Organization: Rob Warnock, Redwood City, CA
Lines: 31

Jerry Aguirre makes a good point of how, by making uucp be full-duplex
(files moving in both directions at once), we could double the traffic
between backbone sites. But he uses this point to suggest we not rush
out to buy 2400-baud modems. Sorry, that's a non-sequitor.

If full-duplex makes it better, then full-duplex at 2400 baud makes
it even BETTER!

However, another possibility one might consider is to note (as Jerry did)
that uucp is essentially half-duplex, make it REALLY be so, and start
using the dial-up 9600-baud half-duplex modems that are now available
for about 1.5-2 times the 2400-baud prices. Do the arithmetic yourself.

(There are buffering/acknowledgement strategies that can make the modem
turn-around delay cause a negligible loss of throughput.  Hint: batching
becomes even more important.)

Note: Some implementations of UNIX have difficulty receiving input
at 9600 baud, but other have shown that that can be fixed by careful
design of the tty drivers and careful attention to interrupt-off
times and latencies. (Unfortunately, it is often other non-tty
drivers, such as disks, which have long hunks of interrupt-off
code in them. It sometimes requires a logic analyzer to find the
actual offenders when you are losing input interrupts.)

Rob Warnock

UUCP:	{ihnp4,ucbvax!amd}!fortune!redwood!rpw3
DDD:	(415)369-7437
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