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Path: utzoo!mnetor!seismo!lll-lcc!well!itivax!m-net!michael
From: michael@m-net.UUCP (Michael McClary)
Newsgroups: comp.dcom.lans
Subject: Re: Ethernet : Broadband vs Baseband
Message-ID: <1062@m-net.UUCP>
Date: Thu, 12-Mar-87 15:17:32 EST
Article-I.D.: m-net.1062
Posted: Thu Mar 12 15:17:32 1987
Date-Received: Mon, 16-Mar-87 04:29:03 EST
References: <2334@sunybcs.UUCP> <18500001@clio> <14863@amdcad.UUCP> <24@kuling.UUCP>
Organization: M-NET, Ann Arbor, MI
Lines: 63
Summary: Electronics is temperature sensitive in baseband, too.

In article <24@kuling.UUCP>, andersa@kuling.UUCP writes:
> In article <14863@amdcad.UUCP> phil@amdcad.UUCP (Phil Ngai) writes:
> >I've stayed away from broadband systems like the plague (who needs
> >modems that stop working because the temperature changed from 75
> >degrees to 70 degrees) but I believe you are wrong about broadband
> >cable usage. 
> 
> Environment dependencies like this seems like a major drawback with
> broadband systems, as compared to baseband ones. Is this particular
> kind of fault verified by experienced broadband users? Are there other
> similar pros and cons to take into consideration?

When GM did the research leading up to the MAP protocol specification,
they decided to go with broadband rather than baseband, because of
temperature problems associated with baseband active cable taps.

In auto plants, the cables must be run near the ceiling, to keep them
out of the way of forklift trucks (which will hit anything automated,
for some strange reason B-) ).  Hitting the main cable takes out the
entire system, while hitting a broadband drop cable only takes out the
drop.  (On ethernet it may also kill power to the tap, which could
adversely affect the main cable, depending on the design of the tap.)

The temperature near the ceiling in many plants is high enough to cause
ethernet's active taps to fail, and a failed tap can take out the whole
cable.  With a broadband system, on the other hand, the taps are passive,
and the few active components (repeater amplifiers) in the environmentally-
exposed parts of the distribution system were designed for outdoor service
in extreme climates.  The modems and headend channel converters, on the
other hand, end up in controlled environments.  (The headend is usually
in an airconditioned computer room, and the modems in offices or inside
the electronic cabinets of machine tools, which have their own air
conditioning.)

I find the complaint about broadband modems flaking out on minor temp
changes surprising.  At the last site where I worked with them (Ford
Ypsilanti), we were using several types of broadband modems designed
by ISI (which became a division of 3M and is now owned by Allen
Bradley).  The one I had the most experience with was the LAN 1, which
has RF electronics designed by an engineer they hired away from Motorola.
In the environments where we ran them (heavily- and lightly-air-conditioned
offices, air-conditioned equipment cabinets) I don't recall a single
failure in the RF modules.  (We did have a power supply go out, a couple
failures in the digital electronics, and a continuing battle with the
firmware, which is excessively paranoid about receiver failure, taking
the modems offline if they temporarily lose communication with the head
end, and requiring manual intervention (local power reset or remote
control by an extra-cost "network monitor" machine) to get them back up.)

A well-designed broadband modem should easily handle any environment
where a computer terminal will operate at all.  Now the complaint
above may mean there are some out there that were designed without
proper attention to RF stability, but at least one vendor has quality
hardware, and it should be possible to find others.

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