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From: bzs@bu-cs.BU.EDU (Barry Shein)
Newsgroups: net.periphs,net.dcom
Subject: 9600 baud modems
Message-ID: <1885@bu-cs.bu-cs.BU.EDU>
Date: Tue, 14-Oct-86 19:10:56 EDT
Article-I.D.: bu-cs.1885
Posted: Tue Oct 14 19:10:56 1986
Date-Received: Mon, 20-Oct-86 14:49:22 EDT
Organization: Boston U. Comp. Sci.
Lines: 52
Xref: watmath net.periphs:1240 net.dcom:2166


I have been using a Microcom (AX/9642?) 9600b modem at home now for
about three months over a normal telephone line.

My experience has been that when it is good, it is very very good and
when it is bad it is awful.

Most of the time it just works, good throughput (more or less 9600b to
my Z19, never measured it but subjectively speaking it's MUCH faster
than 1200 or 2400.)

Then it goes into these lapses where it won't hold a line. It uses
a 'reliable' mode above 2400 (also, optionally, at lower speeds.)
When it has lost synch it does something called "retraining" where
the TST light comes on and it tries to re-establish contact. If this
light comes on for more than about 5 seconds I know I am about to
lose the line.

When it goes into these lapses I sometimes can't hold a line through
a UNIX login. I am not at all sure what causes this but my suspicions
are:

	1. Some of the chips run too hot. I seem to have improved
	things a lot by simply removing the cover.

	2. I notice that I have more trouble if the sun is bright,
	this is weird but night time and cloudy days I seem to have
	little trouble (who knows, it's just an observation.) I don't
	think this is caused by the associated room temperature as
	that has varied a lot (the sun doesn't shine on the modem either,
	could it be causing some sort of noise in the (all above ground)
	telephone lines?)

	3. Sometimes perhaps the line is just noisy, of course.

I tried kermit from my 7300 with it when I first got it. Throughput
was terrible but I suspect the implementation of kermit (I would
re-tune it for fast output before making a judgement.) It did work
however, for what that's worth. I'd rather spend my time developing a
poor-man's SL/IP for it.

The easy redial helps a lot when it is being uncooperative. I must say
it's nice that they have 10e6 tuning variables some of which make little
sense to me (like PBX1 and PBX0 which they seem to recommend trying if
you are having troubles even if there is no PBX is involved.)

The bottom line is I like it a lot better than a 1200b modem I've been
using. I can always drop back to 1200 or 2400 when things get hopeless
and that's maybe 10-20% of the time at most (sometimes I just go read
a book.)

	-Barry Shein, Boston University