[NCLUG] 100 Mbit cabling

[John L. Bass]

Sean Reifschneider <jafo-nclug at tummy.com> writes:
> 100baseT uses pins 1, 2, 3, and 6 in the RJ-45 connector, or two pairs.
> I have had fine luck with running two 100mbps connections or one 100mbps
> and two phone connections on a single 4-pair cat5 cable.  I pulled a
> bunch of cable shortly after we moved into our house, and it's been
> performing quite nicely.

The connect pinouts were actually choosen to allow pins 4 & 5, the center
two, as an RJ11 voice pair. Thus allowing the jack to be used interchangably as
data or voice. Crosstalk for runs under 40' is pretty minimal at 100mbps,
and slightly worse at 10mbps ... small squeal in the voice circuit from
the ethernet packets, almost no affect on the data quality.

Few places actually use voice pairs for RJ11's in RJ45 data jacks anymore,
but it does work pretty well to terminate two runs of CatV into two RJ45's
at the wall plate for combined data/voice in the same RJ45 jack.

The big gotcha, is to make sure you do not unwind more than a 1/2" of the
twist on the data pairs when terminating it at the wall plate jack. The
cross talk at the jack is already a problem, and sharply goes up when you
have an 1" or more of non-twist.

Speeds much above 100mbps on copper have serious limitations, so in the
long run fibre is almost certain to become much more common.

Fibre cable is pretty cheap on Ebay, but expensive to terminate right now.
One strategy if you plan to stay a while is to pull the fibre with the CAT-V
and terminate it in the future when you find a friend with the fibre termination
kit. Gigabit fibrechannel stuff is dead cheap on ebay right now, and IP over
FC is very fast ... fileservers become as fast as local disks, allowing one
to pool storage of all pc/desktop/servers in a location, or build out shared
monster raid arrays. QLogic QLA2200's and Emulex LP8000's both support IP over
FC, and can frequently be found under $100 on ebay - and 6/8 port FC switches
are not much more at times.

John