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From: andrew@jhereg.osa.com (Andrew C. Esh)
Newsgroups: comp.dcom.lans,comp.protocols.tcp-ip
Subject: Re: 10BaseT installation
Message-ID: <1991Apr3.153750.19033@jhereg.osa.com>
Date: 3 Apr 91 15:37:50 GMT
References: <5438@durin.sparta.COM>
Organization: Open Systems Architects, Inc., Mpls, MN
Lines: 38

In article <5438@durin.sparta.COM> frankh@durin.laguna.sparta.com (Frank Halsema) writes:
>I have read a lot about 10BaseT and I am considering using it in a new
>facility. Everything I see has the twisted pair connector as a RJ45 but
>inplications are that twited pair uses two pair or four wires. My
>question is how many pair do I need and if it is two pair why does
>10BaseT use an RJ45 connector. 
>
>
>Frank Halsema                           UUCP: durin!frankh             
>SPARTA, Inc.                   		Internet: frankh@laguna.sparta.com
>23041 de la Carlota, Suite 400
>Laguna Hills Ca, 92653     (714) 768-8161 EXT 339  (714)583-9114 FAX

10baseT tends to be used in the same "wiring closets" (IDF's) as telephone
equipment, as well as the same wall plates, so I would guess the use of
RJ45 is an attempt to make use of existing telephone wiring, without
getting it confused with RJ11.

RJ11 won't work with 10baseT jacks or transceivers, since the pairs are
1-2, and 3-6, with the lines as T+, T-, R+, and R-, respectively. Six wire
RJ45 doesn't work, since you need pin 1 on the 8 wire RJ45. Pin 1 on the
six conductor version connects to pin 2 of the 8 wire outlet. You have to
use an 8 conductor RJ45 to plug into the 10baseT outlets and transceivers.
Which plugs, punchdowns, wires, and connections you use in between the ends
is your business, as long as the connections are fairly secure from EMI
ingress, and the wire has at least 3 twists per foot, preferably more. You
must maintain the pairs, and the polarity, obviously. Some transceivers
will detect backward polarity, and reverse themselves to compensate.
Regular "silver ribbon" telephone wire that they use to make desk-to-wall
cords will cause collisions on a 10baseT connection.

If anyone is interested, I can write a longer posting on the ins and outs
of 10baseT, and the experiences I and my co-workers have had with it.
-- 
Andrew C. Esh			andrew@osa.com
Open Systems Architects, Inc.	
Minneapolis, MN 55416-1528	So much System,
(612) 525-0000			so little CPU time...