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.
