Twisted Pair
Cabling
Twisted-pair
(sometimes known as 10BaseT) is ideal for small, medium, or large
networks that need flexibility and the capacity to expand as the
number of network users grows.
In a twisted-pair
network, computers are arranged in a star pattern. Each PC has a
twisted-pair cable that runs to a centralized hub. Twisted-pair is
generally more reliable than thin coax networks because the hub is
capable of correcting data errors and improving the network's
overall transmission speed and reliability. Also known as uplinking,
hubs can be chained together for even greater expansion.
There are
different grades, or categories, of twisted-pair cabling. Category 5
is the most reliable and widely compatible, and is highly
recommended. It runs easily with 10Mbps networks, and is required
for Fast Ethernet. You can buy Category 5 cabling that is pre-made,
or you can cut & crimp your own.
Category 5 cables
can be purchased or crimped as either straight-through or crossed. A
Category 5 cable has 8 thin, color-coded wires inside that run from
one end of the cable to the other. Only wires 1, 2, 3, and 6 are
used by Ethernet networks for communication. Although only four
wires are used, if the cable has 8 wires, all the wires have to be
connected in both jacks.
Straight-through
cables are used for connecting computers to a hub. Crossed cables
are used for connecting a hub to another hub (there is an exception:
some hubs have a built-in uplink port that is crossed internally,
which allows you to uplink hubs together with a straight cable
instead) or computer to computer without a hub.
In a
straight-through cable, wires 1, 2, 3, and 6 at one end of the cable
are also wires 1, 2, 3, and 6 at the other end. In a crossed cable,
the order of the wires change from one end to the other: wire 1
becomes 3, and 2 becomes 6.
To figure out
which wire is wire number 1, hold the cable so that the end of the
plastic RJ-45 tip (the part that goes into a wall jack first) is
facing away from you. Flip the clip so that the copper side faces up
(the springy clip will now be parallel to the floor). When looking
down on the coppers, wire 1 will be on the far left.
cannot exceed 325 feet in length. Because the cables from all of the
PCs converge at a common point, a 10BaseT network forms a star
configuration, or geometric design, when viewed from above. In the
figure below, three computers are connected together with 10BaseT
cabling and a hub. 
