[UUG/MLUG] Various networking questions:

["McNutt, Justin M." <EMAIL:PROTECTED>]

There have been various networking/cabling questions on here lately.  Here
are some of the answers, answered ad nauseum <grin>:

1)  There are several kinds of Ethernet over CAT5.  One is 10BASE-T, which
uses pairs 1-2, and 3-6.  Another is 100BASE-TX which is 100Mb and uses the
same four wires as 10BASE-T.  Another is 100BASE-T4 which uses all four
pairs in CAT5, and the last is 100BASE-T2, which uses the same four wires as
10BASE-T, but can be used with CAT3 cabling (lower quality).

Only 10BASE-T, 100BASE-TX, and 100BASE-T4 can use autonegotiation.
100BASE-T2 has no standard for that yet.  10BASE-T and 100BASE-TX are the
most common and use only four of the eight wires available in standard CAT5.

2)  If you are going to wire your house, use plenum cable (has to do with
the coating - not the shielding - and fire regulations), and keep it well
away from power lines.  The three feet mentioned before for unshielded
cabling sounds about right.

3)  You can use any single pair of CAT5 for a phone line, for up to three
lines in a jack (RJ11 jacks have only six leads).  This is a good idea since
the twisting in CAT5 gives you better signal quality for your local loop
(the wiring in your house).

4)  You can *try* running 10BASE-T or 100BASE-TX over four of the wires in a
CAT5 cable, and running phones over one or both of the other pairs.  As long
as the jacks are a bit apart, I can't see that there would be much of a
problem, since they use such vastly different frequencies.  Remember that
even a 28.8kbps modem is actually running at 2400 *baud*, but uses phase
modulation to transmit many bits per baud.  So you have the modem at 2400Hz
and the network at 125MHz (100Mb Ethernet).  The signal filters in each set
of devices should keep out the noise (if any) from the other.

Of course, that's theory.  It *should* work, but you'll have to try it.

5)  All you have to do to hook two Ethernet computers together is make (or
buy) a crossover cable.  They can be purchased commercially, you just have
to ask for them sometimes.

Here's the instructions for making your own Ethernet crossover cable (this
is long):

You need a CAT5 patch cord, a crimper with an RJ45 die, and the appropriate
RJ45 tips.  Pay attention to the type of cable you have because there are
different tips for solid cable and stranded cable (is the copper wire a
single solid wire or a lot of little wires?).  Make sure you have the right
die for the tips you're using.  For computer-to-computer, stranded cable is
recommended.

Those parts are available from catalogs, and probably from Insight.com if
you poke around a bit.

For 10BASE-T or 100BASE-TX, look at one end of the cable.  Write down the
colors of the wires *in order* as you see them.  Here's an example:

Pin 1:  Orange
PIn 2:  White-Orange
Pin 3:  Blue
Pin 4:  White-Green
Pin 5:  Green
Pin 6:  White-Blue
Pin 7:  Brown
Pin 8:  White-Brown

Note that 3 and 6 are a pair and 4 and 5 are a pair.  They don't just go
1-2, 3-4, 5-6...

Anyway, chop off the connector at the other end.  Then, using the example
colors above (you'll have to modify these instructions for your cables), you
would insert the wires at the other end into one of the RJ45 tips in this
order:

Pin 1:  Blue
Pin 2:  White-Blue
Pin 3:  Orange
Pin 4:  White-Green
Pin 5:  Green
Pin 6:  White Orange
Pin 7:  Brown
Pin 8:  White-Brown

Note that *pair* 1-2 gets swapped with *pair* 3-6.  Now the transmit pair on
one side goes to the receive pair on the other side, and vice versa.  This
is because usually you have a concentrator (or switch) do this for you, but
since you're going to plug directly into the interface at the other side,
you have to swap the wires yourself.

Anyway, make sure you untwist the wires as little as possible getting them
into the RJ45 tip, and crimp it with the crimper.  Then try it out!

To make a Token Ring crossover, it's pretty much the same thing, but you
have to crossover pairs 3-6 and 4-5 instead.  I don't know about 100BASE-T4,
and I don't think you *can* crossover 1000BASE-T (Gb).  100BASE-2 should be
the same as 100BASE-TX.  I have the specs on all of those somewhere if
somebody's really interested.  <grin>.

Clear as mud?  Hope some of that helps!

--J