Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!apple!netcom!jbreeden
From: jbreeden@netcom.COM (John Breeden)
Newsgroups: comp.dcom.lans
Subject: Re: 10BaseT installation
Message-ID: <1991Apr5.162511.2145@netcom.COM>
Date: 5 Apr 91 16:25:11 GMT
References: <5438@durin.sparta.COM> <14069@darkstar.ucsc.edu> <821@hwsw.gedas.de>
Organization: Netcom - Somewhere in the S.F. Bay Area
Lines: 48

In article <821@hwsw.gedas.de> rainer@hwsw.gedas.de (Rainer Raupach) writes:
>(stuff deleted)
>
>|>      As to why 10BASE-T uses an RJ-45, I know of a couple of reasons, but I
>|>      don't know that any of them are "official."  First and most important,
>|>      it's to keep people from plugging their phones into  data  jacks,  and
>|>      vice  versa. Secondly, it's to allow for people in the future plugging
>|>      their phones into data jacks, but making it work.   You'll  find  that
>|>      ISDN normally uses pins 4, 5, 7, and 8.
>|>                               
>|>                              -Bill Woodcock
>|>                               BMUG NetAdmin
>
>Additional to these reasons, there are some more:
>AT&T uses some more pins to include some other features, like
>SQE-testing and link integrity testing. I really don't know, if 
>those features are part of the 10 Base T - standard.
>

RJ45s are used because the original concept of 10baseT was to use the exist-
ing TELEPHONE wiring - and there's been a TELEPHONE wiring standard in use
for years now .... AT&T's PDS (Premise Distribution System).

PDS states that pins 4,5,7 & 8 are for voice and 1,2,3 & 6 are for data (pin
1 is on the extreme left when viewing a RJ45 head on with the little clippy
thing pointing down).

How prevelent is the use of this standard? Look at any install over the past
10 years of an AT&T, Northern Telecom or Rolm PBX and the wiring is PDS
standard (I think these three should represent about 90% of the big PBX
installs).

The PDS wiring standard was also picked up as the wiring to the desk for 
ISDN (B channel).

It also includes a "standard" for transporting both async and sync terminal
traffic over the same 4 pair UTP.

AT&T recently introduced a UTP "super wire" that they claim will transport
16 mb token ring for 300 feet using the same 2 data pairs.

-- 
 John Robert Breeden, 
    jbreeden@netcom.com, apple!netcom!jbreeden, ATTMAIL:!jbreeden
 -------------------------------------------------------------------
 "The nice thing about standards is that you have so many to choose 
  from. If you don't like any of them, you just wait for next year's 
  model."