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3.1 | |
Copper Media | |
| 3.1.9 | |
UTP cable |
Unshielded twisted-pair cable (UTP)
 is a
four-pair wire medium used in a variety of networks. Each of the 8
individual copper wires in the UTP cable is covered by insulating
material. In addition, each pair of wires is twisted around each
other. This type of cable relies solely on the cancellation effect
produced by the twisted wire pairs, to limit signal degradation caused
by EMI and RFI. To further reduce crosstalk between the pairs in UTP
cable, the number of twists in the wire pairs varies. Like STP cable,
UTP cable must follow precise specifications as to how many twists or
braids are permitted per foot of cable.
TIA/EIA-568-A contains specifications governing cable performance. It calls for running two cables, one for voice and one for data, to each outlet. Of the two cables, the one for voice must be four-pair UTP. CAT 5 is the one most frequently recommended and implemented in installations today. Unshielded twisted-pair cable has many
advantages. It is easy to install and is less expensive than other
types of networking media. In fact, UTP costs less per meter than any
other type of LAN cabling.
UTP was once considered slower at transmitting data than other types of cable. This is no longer true. In fact, today, UTP is considered the fastest copper-based media. When communication occurs, the signal that is transmitted by the source needs to be understood by the destination. This is true from both a software and physical perspective. The transmitted signal needs to be properly received by the circuit connection designed to receive signals. The transmit pin of the source needs to ultimately connect to the receiving pin of the destination. The following are the types of cable connections used between internetwork devices. In Figure
In Figure
In Figure
The cables are defined by the type of
connections, or pinouts, from one end to the other end of the cable.
See images two, four, and six. A technician can compare both ends of
the same cable by placing them next to each other, provided the cable
has not yet been placed in a wall. The technician observes the colors
of the two RJ-45 connections by placing both ends with the clip placed
into the hand and the top of both ends of the cable pointing away from
the technician. A straight through cable should have both ends with
identical color patterns. While comparing the ends of a cross-over
cable, the color of pins #1 and #2 will appear on the other end at pins #3
and #6, and
vice-versa. This occurs because the transmit and receive pins are in
different locations. On a rollover cable, the color combination from
left to right on one end should be exactly opposite to the color
combination on the other end.
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However,
the real advantage is the size. Since it has such a small external
diameter, UTP does not fill up wiring ducts as rapidly as other types
of cable. This can be an extremely important factor to consider,
particularly when installing a network in an older building. In
addition, when UTP cable is installed using an RJ-45 connector,
potential sources of network noise are greatly reduced and a good
solid connection is practically guaranteed. There are disadvantages in
using twisted-pair cabling. UTP cable is more prone to electrical
noise and interference than other types of networking media, and the
distance between signal boosts is shorter for UTP than it is for
coaxial and fiber optic cables. 
, a
LAN switch is connected to a computer. The cable that connects
from the switch port to the computer NIC port is called a
straight-through cable.
, two
switches are connected together. The cable that connects
from one switch port to another switch port is called a crossover cable.
, the cable
that connects the RJ-45 adapter on the com port of the computer to the console port of the router or switch is called a
rollover cable. 
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