Network Cabling 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.
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 EIA/TIA (Electronic Industry Association/Telecommunication
Industry Association) has established standards of UTP and rated five categories of wire.
One difference between the different categories of UTP is the tightness of the twisting
of the copper pairs. The tighter the twisting, the higher the supported transmission rate
and the greater the cost per foot. Buy the best cable you can afford; most schools
purchase Category 3 or Category 5e. Category 5e cable is highly recommended.
If you are designing a 10 Mbps Ethernet network and are considering the cost savings of
buying Category 3 wire instead of Category 5e, remember that the Category 5e cable will
provide more "room to grow" as transmission technologies increase. Both category
3 and category 5e UTP have a maximum segment length of 100 meters. 10BaseT refers to the specifications for unshielded
twisted pair cable (category 3, 5e, or 6) carrying Ethernet signals.
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
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 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.
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 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:
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.
Not all networks are connected with cabling; some networks are wireless. Wireless LANs
use high frequency radio signals or infrared light beams to communicate between the
workstations and the file server. 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 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.
Wireless LANs also have some disadvantages. They are very expensive, provide poor
security, and are susceptible to electrical interference from lights and radios. They are
also slower than LANs using cabling.
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.
