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Path: utzoo!linus!decvax!ittvax!dcdwest!sdcsvax!sdcrdcf!hplabs!oliveb!jerry
From: jerry@oliveb.UUCP (Jerry Aguirre)
Newsgroups: net.news,net.dcom
Subject: 2400 baud modems and uucp inefficiencies
Message-ID: <184@oliveb.UUCP>
Date: Mon, 1-Oct-84 19:47:32 EDT
Article-I.D.: oliveb.184
Posted: Mon Oct  1 19:47:32 1984
Date-Received: Wed, 3-Oct-84 06:42:43 EDT
Organization: Olivetti ATC, Cupertino, Ca
Lines: 40

There have been some articles posted lately about the advantages of
using 2400 baud modems for the distribution of news.  Before someone
spends money to upgrade their modems consider that the same effect
could be had by improving the software involved.

I will ignore for the moment the news software and the relative
efficiencies of batching, compression, and "I have/send me"
distribution.  Instead I want to examine the efficiencies of uucp
itself.

Uucp uses a fairly efficient protocol.  It places the line in RAW mode
so that data can be sent without escapes.  It buffers multiple packets
so that turn-around delays are eliminated.  If I examine the uucp log
entries I see entries like 109 bytes per second of transmission.  If a
1200 baud modem gives 120 bytes per second then the efficiency should
be 109/120=90%.  This sounds pretty good.

But, it is still only using half the bandwidth available!  Remember
that this is a full duplex modem.  It really allows 1200 baud in EACH
direction so the real bandwidth is 1200 baud x 2 directions = 2400
baud!  Bet you didn't know you already had 2400 baud modems.

However uucp does not make use of the full duplex capability.  It
insists on sending files in one direction at a time.  The only data
coming back are the packet acknowledgements which consume about 12%
of the available bandwidth.  Just watch the send/receive lights on your
modem.  The send light comes on solid but the receive light flickers on
and off (mostly off).

Presumably two backbone sites would have roughly equal amounts of news
to send to each other.  If the sending and receiving could be
overlapped then the time consumed could be cut by almost half.

As uucp does protocol negotiation perhaps a new "full duplex" protocol
could be added as a preferred option.  The advantage is that the
improvement could be made available to all sites instead of just those
that can afford expensive modems.

					    Jerry Aguirre
{hplabs|fortune|idi|ihnp4|ios|tolerant|allegra|tymix}!oliveb!jerry