Path: utzoo!mnetor!uunet!unisoft!mtxinu!ed
From: ed@mtxinu.UUCP (Ed Gould)
Newsgroups: comp.dcom.lans
Subject: Re: Thinwire ethernet: Question about drop cables
Message-ID: <575@mtxinu.UUCP>
Date: 22 Mar 88 07:09:22 GMT
References: <4491@june.cs.washington.edu> <13328@uflorida.cis.ufl.EDU>
Reply-To: ed@mtxinu.UUCP (Ed Gould)
Organization: mt Xinu, Berkeley
Lines: 27

>>I have a question about thinwire ethernet. Is it possible
>>to insert a drop cable between the t-tap on the ethernet and the
>>transceiver tap on a controller's on-board trasceiver? If so,
>>what are the length limitations on this drop cable?

>Yea, you can do that. I couldn't find the exact specification in the Digital/
>Intel/Xerox v2.0 Ethernet Specifications Manual - all it talks about is the
>thick Etherhose. But from expirenece we have made drop cables up to about
>8 feet long and they seem to be working okay . . .

It is a violation of the Ethernet specs to do so, although it may work
in some circumstances.  The spec is that the distance from the center
conductor to the transciever (embedded in the controller in the case of
T-tapped thinwire) must be less than some very small number (about 2cm
if I remember correctly).

The Ethernet spec is loaded with tradeoffs:  The system is reasonably
well guaranteed to work if the spec is followed carefully even when
pushed to the limit.  However, it's not often obvious what spec trades
off against which other.  Violating some specs might work; violating
the wrong combination won't.

-- 
Ed Gould                    mt Xinu, 2560 Ninth St., Berkeley, CA  94710  USA
{ucbvax,uunet}!mtxinu!ed    +1 415 644 0146

"`She's smart, for a woman, wonder how she got that way'..."