What is Network Cabling?
Cable is the medium
through which information usually moves from one network device to another.
There are several types of cable which are commonly used with LANs. In some
cases, a network will utilize only one type of cable, other networks will use a
variety of cable types. The type of cable chosen for a network is related to
the network's topology, protocol, and size. Understanding the characteristics
of different types of cable and how they relate to other aspects of a network
is necessary for the development of a successful network.
Type
of cables-
·
Twisted Pair
·
Coaxial Cable
·
Fiber Optic Cable
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). The following sections discuss UTP and STP cable in more detail.
Unshielded Twisted-Pair Cable-
The quality of UTP may vary from telephone-grade
wire to extremely high-speed cable. The cable has four pairs of wires inside
the jacket. Each pair is twisted with a different number of twists per inch to
help eliminate interference from adjacent pairs and other electrical devices.
The tighter the twisting, the higher the supported transmission rate and the
greater the cost per foot. The EIA/TIA (Electronic Industry
Association/Telecommunication Industry Association) has established standards
of UTP and rated six categories of wire (additional categories are emerging).
Shielded Twisted-Pair Cable-
Shielded twisted-pair (STP) cable combines the techniques of shielding, cancellation, and wire
twisting. Each pair of wires is wrapped in a metallic foil .The four pairs of
wires then are wrapped in an overall metallic braid or foil, usually 150-ohm
cable. As specified for use in Ethernet network installations, STP reduces
electrical noise both within the cable (pair-to-pair coupling, or crosstalk)
and from outside the cable (EMI and RFI). STP usually is installed with STP
data connector, which is created especially for the STP cable. However, STP
cabling also can use the same RJ connectors that UTP uses. Although STP
prevents interference better than UTP, it is more expensive and difficult to
install. In addition, the metallic shielding must be grounded at both ends. If
it is improperly grounded, the shield acts like an antenna and picks up
unwanted signals. Because of its cost and difficulty with termination, STP is
rarely used in Ethernet networks. STP is primarily used in Europe.
Coaxial Cable-
Coaxial cabling has a single copper conductor at its center. A
plastic layer provides insulation between the center conductor and a braided
metal shield (See fig. 3). The metal shield helps to block any outside
interference from fluorescent lights, motors, and other computers.
Although coaxial cabling is difficult to install, it is highly
resistant to signal interference. In addition, it can support greater cable
lengths between network devices than twisted pair cable. The two types of
coaxial cabling are thick coaxial and thin coaxial.
Thin coaxial cable is also referred to as thinnet. 10Base2 refers
to the specifications for thin coaxial cable carrying Ethernet signals. The 2
refers to the approximate maximum segment length being 200 meters. In actual
fact the maximum segment length is 185 meters. Thin coaxial cable has been
popular in school networks, especially linear bus networks.
Thick coaxial cable is also referred to as thicknet. 10Base5
refers to the specifications for thick coaxial cable carrying Ethernet signals.
The 5 refers to the maximum segment length being 500 meters. Thick coaxial
cable has an extra protective plastic cover that helps keep moisture away from
the center conductor. This makes thick coaxial a great choice when running
longer lengths in a linear bus network. One disadvantage of thick coaxial is
that it does not bend easily and is difficult to install.
Fiber Optic Cable-
Fiber optic cabling consists of a center glass core surrounded by
several layers of protective materials It transmits light rather than
electronic signals eliminating the problem of electrical interference. This
makes it ideal for certain environments that contain a large amount of
electrical interference. It has also made it the standard for connecting
networks between buildings, due to its immunity to the effects of moisture and
lighting.
Fiber optic cable has the ability to transmit signals over much
longer distances than coaxial and twisted pair. It also has the capability to
carry information at vastly greater speeds. This capacity broadens
communication possibilities to include services such as video conferencing and
interactive services. The cost of fiber optic cabling is comparable to copper
cabling; however, it is more difficult to install and modify. 10BaseF refers to
the specifications for fiber optic cable carrying Ethernet signals.
The center core of fiber cables is made from glass or plastic
fibers. A plastic coating then cushions the fiber center, and kevlar fibers
help to strengthen the cables and prevent breakage. The outer insulating jacket
made of Teflon or PVC.