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.
The following sections discuss the types of cables used
in networks and other related topics.
Unshielded Twisted Pair (UTP) Cable
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
(See fig. 1).
Fig.1. 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 five
categories of wire.
Categories of Unshielded Twisted Pair
| Type |
Use |
| Category 1 |
Voice Only (Telephone Wire) |
| Category 2 |
Data to 4 Mbps (LocalTalk) |
| Category 3 |
Data to 10 Mbps (Ethernet) |
| Category 4 |
Data to 20 Mbps (16 Mbps Token Ring) |
| Category 5 |
Data to 100 Mbps (Fast Ethernet) |
|
Buy the best cable you can afford; most schools purchase
Category 3 or Category 5. If you are designing a 10 Mbps
Ethernet network and are considering the cost savings of
buying Category 3 wire instead of Category 5, remember that
the Category 5 cable will provide more "room to grow" as
transmission technologies increase. Both Category 3 and
Category 5 UTP have a maximum segment length of 100 meters.
In Florida, Category 5 cable is required for retrofit
grants. 10BaseT refers to the specifications for unshielded
twisted pair cable (Category 3, 4, or 5) carrying Ethernet
signals. Category 6 is relatively new and is used for
gigabit connections.
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 (See fig.
2). 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.
Fig. 2. RJ-45 connector
Shielded Twisted Pair (STP) Cable
A disadvantage of UTP is that it may be susceptible to
radio and electrical frequency interference. Shielded
twisted pair (STP) is suitable for environments with
electrical interference; however, the extra shielding can
make the cables quite bulky. Shielded twisted pair is often
used on networks using Token Ring topology.
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.
Fig. 3. Coaxial cable
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 is
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.
Coaxial Cable Connectors
The most common type of connector used with coaxial
cables is the Bayone-Neill-Concelman (BNC) connector (See
fig. 4). Different types of adapters are available for BNC
connectors, including a T-connector, barrel connector, and
terminator. Connectors on the cable are the weakest points
in any network. To help avoid problems with your network,
always use the BNC connectors that crimp, rather than screw,
onto the cable.
Fig. 4. BNC
connector
Fiber Optic Cable
Fiber optic cabling consists of a center glass core
surrounded by several layers of protective materials (See
fig. 5). 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.
Fig.5. Fiber optic
cable
Facts about fiber optic cables:
- Outer insulating jacket is made of Teflon or PVC.
- Kevlar fiber helps to strengthen the cable and prevent
breakage.
- A plastic coating is used to cushion the fiber center.
- Center (core) is made of glass or plastic fibers.
Fiber Optic Connector
The most common connector used with fiber optic cable is
an ST connector. It is barrel shaped, similar to a BNC
connector. A newer connector, the SC, is becoming more
popular. It has a squared face and is easier to connect in a
confined space.
Ethernet Cable Summary
| Specification |
Cable Type |
Maximum length |
| 10BaseT |
Unshielded Twisted Pair |
100 meters |
| 10Base2 |
Thin Coaxial |
185 meters |
| 10Base5 |
Thick Coaxial |
500 meters |
| 10BaseF |
Fiber Optic |
2000 meters |
| 100BaseT |
Unshielded Twisted Pair |
100 meters |
| 100BaseTX |
Unshielded Twisted Pair |
220 meters |
|
Wireless LANs
Not all networks are connected with cabling; some
networks are wireless. Wireless LANs use high frequency
radio signals, infrared light beams, or lasers to
communicate between the workstations and the file server or
hubs. Each workstation and file server on a wireless network
has some sort of transceiver/antenna to send and receive the
data. Information is relayed between transceivers as if they
were physically connected. For longer distance, wireless
communications can also take place through cellular
telephone technology, microwave transmission, or by
satellite.
Wireless networks are great for allowing laptop computers
or remote computers to connect to the LAN. Wireless networks
are also beneficial in older buildings where it may be
difficult or impossible to install cables.
The two most common types of infrared communications used
in schools are line-of-sight and scattered broadcast.
Line-of-sight communication means that there must be an
unblocked direct line between the workstation and the
transceiver. If a person walks within the line-of-sight
while there is a transmission, the information would need to
be sent again. This kind of obstruction can slow down the
wireless network.
Scattered infrared communication is a broadcast of
infrared transmissions sent out in multiple directions that
bounces off walls and ceilings until it eventually hits the
receiver. Networking communications with laser are virtually
the same as line-of-sight infrared networks.
Wireless LANs have several disadvantages. They provide
poor security, and are susceptible to interference from
lights and electronic devices. They are also slower than
LANs using cabling.
Installing Cable - Some Guidelines
When running cable, it is best to follow a few simple
rules:
- Always use more cable than you need. Leave plenty of
slack.
- Test every part of a network as you install it. Even
if it is brand new, it may have problems that will be
difficult to isolate later.
- Stay at least 3 feet away from fluorescent light boxes
and other sources of electrical interference.
- If it is necessary to run cable across the floor,
cover the cable with cable protectors.
- Label both ends of each cable.
- Use cable ties (not tape) to keep cables in the same
location together.
I.T.
Education Guide
