Twisted pair cabling comes in
two varieties: shielded and unshielded. Unshielded twisted pair (UTP) is the
most popular and is generally the best option for school networks.
Unshielded Twisted Pair
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).
Categories of Unshielded
Twisted Pair
Unshielded Twisted Pair
Connector
The standard connector for
unshielded twisted pair cabling is an RJ-45 connector. This is a plastic
connector that looks like a large telephone-style connector. A slot allows the
RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that
the connector follows a standard borrowed from the telephone industry. This
standard designates which wire goes with each pin inside the connector.
Shielded Twisted Pair (STP)
Cable
Although UTP cable is the least
expensive cable, it may be susceptible to radio and electrical frequency
interference (it should not be too close to electric motors, fluorescent
lights, etc.). If you must place cable in environments with lots of potential
interference, or if you must place cable in extremely sensitive environments
that may be susceptible to the electrical current in the UTP, shielded twisted
pair may be the solution. Shielded cables can also help to extend the maximum
distance of the cables.
Shielded twisted pair cable is
available in three different configurations:
Each pair of wires is
individually shielded with foil.
There is a foil or braid shield
inside the jacket covering all wires (as a group).
There is a shield around each
individual pair, as well as around the entire group of wires (referred to as
double shield twisted pair).
Coaxial Cable
Coaxial cable is an early
version of the way computers were connected to a network and it worked well. It
is the cable in cable TV. This cabling has a single copper conductor at its
center. It allows higher data transmission rates over long distances.
A plastic layer provides
insulation between the center conductor and a braided metal shield. The outer
shield is used as an electrical ground that simultaneously protects the inner
core from the interference.
Coaxial cable can transmit up
to 10Mbps for a distance of up to 500 meters. The main drawback of this type of
cable is its inflexibility and low security, but it requires little maintenance
and its simple to install. It also provides better resistance to electrical
noise over long distance, and its electronic support components are affordable.
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.
There are two common types of
fiber cables -- single mode and multimode. Multimode cable has a larger
diameter; however, both cables provide high bandwidth at high speeds. Single
mode can provide more distance, but it is more expensive.
