Page 110 - DMGT505_MANAGEMENT_INFORMATION_SYSTEM

Unit 6: Business Networks and Telecommunications

to around 2.0 dB loss per connection point, depending on how well the connection has been Notes
made. If your connectors or fiber splices are poorly made, or if there is finger oil or dust on the
connector ends, then you can have higher optical loss on the segment.
The older FOIRL segment typically used the same type of fiber optic cable, connectors, and had
the same optical loss budget. The 10BASE-FL specifications were designed to allow backward
compatibility with existing FOIRL segments. The major difference is that the 10BASE-FL segment
may be up to 2,000 meters in length if only 10BASE-FL equipment is used on the segment.

Network media is the actual path over which an electrical signal travels as it moves from one
component to another. This unit describes the common types of network media, including
twisted-pair cable, coaxial cable, fiber-optic cable, and wireless.

6.4.1 Twisted-pair Cable

Twisted-pair cable is a type of cabling that is used for telephone communications and most
modern Ethernet networks. A pair of wires forms a circuit that can transmit data. The pairs are
twisted to provide protection against crosstalk, the noise generated by adjacent pairs. When
electrical current flows through a wire, it creates a small, circular magnetic field around the
wire. When two wires in an electrical circuit are placed close together, their magnetic fields are
the exact opposite of each other. Thus, the two magnetic fields cancel each other out. They also
cancel out any outside magnetic fields. Twisting the wires can enhance this cancellation effect.
Using cancellation together with twisting the wires, cable designers can effectively provide self-
shielding for wire pairs within the network media.
Two basic types of twisted-pair cable exist: Unshielded twisted pair (UTP) and Shielded twisted
pair (STP).

Unshielded Twisted Pair (UTP) Cable

UTP cable is a medium that is composed of pairs of wires (see Figure 6.7). UTP cable is used in a
variety of networks. Each of the eight individual copper wires in UTP cable is covered by an
insulating material. In addition, the wires in each pair are twisted around each other.

Figure 6.7: Unshielded Twisted-Pair Cable

UTP cable relies solely on the cancellation effect produced by the twisted wire pairs to limit
signal degradation caused by electromagnetic interference (EMI) and radio frequency interference
(RFI). To further reduce crosstalk between the pairs in UTP cable, the number of twists in the
wire pairs varies. UTP cable must follow precise specifications governing how many twists or
braids are permitted per meter (3.28 feet) of cable.
UTP cable often is installed using a Registered Jack 45 (RJ-45) connector (see Figure 6.8). The RJ-
45 is an eight-wire connector used commonly to connect computers onto a local-area network
(LAN), especially Ethernets.

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