Rick Clark wrote:
>
> I understand completely. We have the same setup in our buildings.
> It [Cat5 cable] is nothing more than hardware that is rated and
> tested for 10baseT.

True, it is just cable, but it has no relation to 10BaseT directly.
The EIA/TIA Category classifications are based on impedence (100 ohm),
crosstalk (overall plus near-end [NEXT]), and other engineering
specifications that must be met for specific frequency spectra.  In
short, the ratings are:

   Category 3: 16Mhz, suited for 10Mb ethernet/4Mb token ring
   Category 4: 20Mhz, includes 16Mb token ring
   Category 5: 100Mhz, includes 100Mb ethernet

The key difference between 'Category' cable and telephone wire/serial
cables is that 'Category' cables are twisted pairs, to eliminate
crosstalk and enhance signal propagation.  'Category' cable can carry
anything telephone wire or serial cable did just as well, it is just
a matter of getting a 3-wire transmit/receive/ground, or a 2-pair
10BaseT transmit/receive, etc., from point A to point B.

RJ45 plugs are "just a plug".  If you know the wiring scheme and which
pins go where, you can translate one to another, just as the age-old
DB25 RS-232 has been implemented in the more recent DB9, or the round
Macintosh connector, or yes, an RJ45 or RJ11.  The important part is
that the affected parties agree on a wiring standard from end-to-end.

Most building wiring now done with Cat5 is stringently regulated by
the EIA/TIA-568A specification (or 568B).  Search the web :-)  And
as how the various circuits are terminated/separated in the wiring
closet, EIA/TIA-569.

I saw further down in this thread the RJ11 vs RJ45 discussion.  RJ11
does provide enough wiring for a basic serial connection, but you run
a very real danger of having a clueless user plugging a serial data
cable into a telephone jack.  The 48-volt ringer signal can wreck an
unsuspecting terminal :-(  This is where your choice of pairs to use
for specific applications becomes very important.

Jeff Kell <[log in to unmask]>