Page 79 - DLIS408_INFORMATION_TECHNOLOGY-APPLICATIONSL SCIENCES

Information Technology and Application

Notes There are two types of Twisted-pair cables—Unshielded and Shielded.
(i) Unshielded Twisted-pair (UTP) Cable. It consists of a set of twisted pairs with a simple
plastic encasement. It is the most popular communication medium and is commonly used
in telephone systems.
Advantages of UTP cable—A UTP cable offers the following benefits:
The cost of UTP is extremely low compared to other communications media.
The UTP installation equipment is inexpensive and widely available.
The UTP cables can be adequately installed with very little training.
Drawbacks of UTP cable—A UTP cable has the following drawbacks:
Though UTP cable is suitable to transmit data at 1-2 Mbps (Megabits per second) over
a distance of 1 Km or more, but as speed increases, the maximum transmission
distance reduces. So, a large number of repeaters (equipment’s for boosting the
signals) are needed to send data over a long distances and hence the cost of installa-
tion and maintenance of UTP cables (especially for long distance) becomes high.
Although the twists in UTP cable greatly reduce cross talk (an electromagnetic inter-
ference between two copper wires conducting electrical signals in close proximity),
a certain amount of interference exists between pairs of wires.
(ii) Shielded Twisted-pair (STP) Cable. A shielded Twisted-pair cable is an insulated cable,
which includes bundled pairs wrapped in a foil shielding. Although UTP cable is com-
monly used, STP cable (introduced by IBM in the early 1980s) is used in Some IBMJ instal-
lations. The differences between UTP and STP cables are described in Table 6.1

Table 6.1 Difference between UTP and STP cable.
Table 6.1: Difference between UTP and STP cable.
Unshielded Twisted-pair Cable Shielded Twisted-pair Cable
1. UTP cable consists of a set of 1. STP cable consists of bundled pairs
twisted Pairs with a simple plastic wrapped in a foil shielding.
encasement.
2. UTP cable is easier to install. 2. STP cable is more difficult to install
thanUTP Cable.
3. It is cheaper than STP cable. 3. It is costlier than UTP cable.
4. UTP cable transmits data at lesser 4. STP cable transmits data at greater
Speed(1-2 Mbps). speed(16 Mbps).
5. Cross talk is more in UTP cable. 5. Cross talk is less in STP cables due to foil.

Uses of Twisted-paid Cable. Twisted-pair cable is widely used in the telephone networks. Most
PCs were connected to Internet over telephone wires and modems (equipment that convert digital
signals to analog and vice-versa). Modem connections that use standard telephone wire provide
band widths (transmission capacities of communication channels) ranging from 9600 bps to about
56 Kbps, sufficient for ordinary data communications.

6.5.3 Coaxial Cable
Coaxial cable or coax is an another common transmission medium. It has better shielding than
twisted-pair cable, so it can provide higher speed over longer distance. A coaxial cable as shown in
Figure 6.5 consists of the following four parts:
(i) Core. The innermost part of a coaxial cable is the core made up of a stiff copper wire.
(ii) Insulator. The core is surrounded by a sheath of insulation. Insulation allows co-axial cable
to carry more information than Twisted-pair cable.
(iii) Conductor. The sheath is surrounded by a cylindrical conductor often as a closely woven
braided mesh. The conductor conducts and shields against interference.
(iv) Protective Sheath. The conductor is covered in a protective plastic sheath.
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