Information Technology Reference
In-Depth Information
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The reliability of the cable.
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The maximum length between nodes.
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The possibility of electrical hazards and tolerance to harsh conditions.
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Power loss in the cables.
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Expense and general availability of the cable.
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Ease of connection, maintenance and ease of running cables.
The main types of cables used in networks are twisted-pair, coaxial and fibre optic; these are
illustrated in Figure 25.12. Twisted-pair and coaxial cables transmit electrical signals,
whereas fibre optic cables transmit light pulses.
Insulating outer cond uctor
Inner
conductor
M etal sheath
Coaxial
cable
O uter cladding
(PVC )
Inner cladding
(glass)
Inner fib re
(glass)
Fibre
optic
cable
Tw isted-pair
cable
Figure 25.12
Typical network cable types
The basic specification for the cable types are:
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Twisted-pair cables - unshielded twisted-pair (UTP) cables are not shielded and thus
interfere with nearby cables, whereas, shielded twisted-pair (STP) cables have a less ef-
fect on nearby cables. Public telephone lines generally use UTP cables. In LANs, they
are generally used up to bit rates of 100 Mbps and with maximum lengths of 100 m.
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Coaxial cables - these have a grounded metal sheath around the signal conductor. This
limits the amount of interference between cables and thus allows higher data rates. Typi-
cally, they are used at bit rates of 100 Mbps for maximum lengths of 1 km.
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Fibre optic cables - having the highest specifications of the three types, they allow ex-
tremely high bit rates over long distances. Fibre optic cables do not interfere with nearby
cables and give greater security, give more protection from electrical damage from by
external equipment, are more resistance to harsh environments and are safer in hazard-
ous environments. A typical bit rate for a LAN using fibre optic cables is 100 Mbps, in
other applications this can reach several gigabits/per second. The maximum length of the
fibre optic cable depends on the transmitter and receiver electronics, but a single length
of 20 km is possible.
