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Patch Cabling
- Theory & General Netwoking
Information
There are three wiring options, called T568A, T568B,
and USOC.
T568A is supposedly "preferred" (though I've heard
that T568B may be more common)
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Plug / Jack - RJ45 - 568B
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If you're looking at the contact end of a plug with
the latch down, pin 1 is on the right.
If you're looking at the wiring end of a plug with the
latch down, pin 1 is on the left.
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Plug / Jack - RJ45 - 568A
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If you're looking at the contact end of a plug with
the latch down, pin 1 is on the right.
If you're looking at the wiring end of a plug with the
latch down, pin 1 is on the left.
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Sockets / Wall Plates
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Pin layout varies from make to make
use the pin numbers or colour codes provided.
Ensure you keep to 568B or 568A
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Wiring Colors
and Signals:
The transmit data (TX) and receive
data (RX) signals on each pair of a 100BaseTX segment
are polarized, with one wire of each signal pair carrying
the positive (+) signal, and the other carrying the
negative (-) signal. Colors may vary by manufacturer.
This is just an example of what you might see.
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258B
RJ45 pins
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Color |
Signal |
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258A
RJ45 pins
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Color |
Signal |
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1
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white/orange |
TX+ |
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1
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white/green |
RX+ |
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2
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orange |
TX- |
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2
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green |
RX- |
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3
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white/green |
RX+ |
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3
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white/orange |
TX+ |
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4
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blue |
Unused |
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4
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blue |
Unused |
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5
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white/blue |
Unused |
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5
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white/blue |
Unused |
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6
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green |
RX- |
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6
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orange |
TX- |
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7
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white/brown |
Unused |
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7
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white/brown |
Unused |
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8
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brown |
Unused |
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8
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brown |
Unused |
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Cat 5 core pair colours
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blue
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white/blue
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green |
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white/green |
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orange |
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white/orange |
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brown |
/ |
white/brown |
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CAT5 signals are "balanced": the striped and
solid wires in a pair carry the same information negated,
so their magnetic fields tend to cancel.
Unlike phone wires, CAT5 wires do not cross over; the
same wires go to the same pin numbers at all connectors.
This works because hubs all have internal crossovers.
Hub-to-hub interconnects need a special crossover cable,
as does a hub-to-DSL-router connection, or a 2-node hubless
network.
See patch cables for the
details of making a crossover cable; if you make one,
mark it so clearly that you'll never confuse it.
Q: Can I install Cat 5 cable over a distance
longer than 90 meters and still certify the system as
Cat5?
A: Although some cables are advertised as being
tested beyond 90 meters, please be aware that the industry
standards state that horizontal runs should NOT
exceed the 90 meters
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Star topology
Old style Ethernet bus wiring (i.e., taking the cable
from one machine to the next, and then to the next, etc.)
is prone to cable failure and quickly consumes allowed
distances due to aesthetic wiring needs. If the wiring
connection is broken at any point, the entire network
(segment) fails - and the much greater number of connections
increases the probability of a failure or break. On the
other hand, it's pretty easy to do for a layman and may
involve less actual wiring for small segments.
Star wiring eliminates the single point of failure
of a common wire. A central hub has many connections
that radiate out to hosts, if one of these hosts connections
fails it usually doesn't affect the others. Obviously,
however, the hub becomes a central point of failure
itself, but studies show a quality hub is less likely
to fail before a heavily used strand of coax.
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Never pull / stretch CAT5 wire with more than
25 pounds of force.
Never step on or otherwise crush, kink, or crimp
the wire (don't make staples or wire ties tight).
Never put a staple through the wire (you knew that,
I'll bet).
Avoid periodic sags; if the cable must sag, vary
the intervals.
If you bundle a group of cables together with cable ties,
do not over-cinch them. It's okay to snug them together
firmly; but don't tighten them so much that you deform
the cables.
Never bend CAT5 wire tightly around a corner; make
sure it bends gradually, so that a whole circle would
be at least 2" across. Watch especially when the
wire comes out a drilled hole and turns; don't let knots
or kinks happen even temporarily.
Don't put so many wires in any conduits that it
ends up more than 40% full.
Keep cables away from devices which can introduce
noise into them. Here's a short list: copy machines, electric
heaters, speakers, printers, TV sets, fluorescent lights,
copiers, welding machines, microwave ovens, telephones,
fans, electric ovens, dryers, washing machines, and shop
equipment.
Never untwist the 2 wires in a single pair for
more than 1/3-1/2" to make a connection (the twists
are critical to cancel out interference between the wires).
Try to avoid running cables parallel to power cables
and never run the wire parallel to power wiring nearer
than 6" away.
No run (hub to device) may be over 90 meters long
Do not run UTP cable outside of a building. It
presents a very dangerous lightning hazard! |
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