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From: woody@ucscb.UCSC.EDU (Bill Woodcock)
Newsgroups: comp.dcom.lans,comp.protocols.tcp-ip
Subject: Re: 10BaseT installation
Message-ID: <14069@darkstar.ucsc.edu>
Date: 3 Apr 91 08:11:08 GMT
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Organization: University of California, Santa Cruz
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         > 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 twisted 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.
     
     10BASE-T does indeed use four conductors.  On an RJ-45  modular  jack,
     pin  1  is Rx+, pin 2 is Rx-, pin 3 is Tx+, and pin 6 is Tx-. When you
     go to your wiring closet, they are normally punched down in that order
     as  well, pin 1 to row 1, pin 2 to row 2, pin 3 to row 3, and pin 6 to
     row 4.
     
     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

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