1.5.2 Network Components

Cabling

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
Shielded Twisted Pair (STP) Cable
Coaxial Cable
Fiber Optic Cable
Wireless LANs

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).

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

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.

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).

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 interferenc 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 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

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.

Do you recognize the cable connector if you have ever fiddled with TV arials or the cable internet point in your home.

Fibre Optic Cable

Fibre optic cabling consists of a central glass core surrounded by several layers of protective materials.

It transmits light rather than electronic signals - eliminating the problem of electrical interference.

Therefore, it is ideal for environments that have 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.

Fibre 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.
- Which enables use of 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.

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 fibre centre.
- Center (core) is made of glass or plastic fibres.

Fiber Optic Connector

There are a wide variety of connectors for fibrew optic cable.

The most common connector used with fiber optic cable is an ST connectere or.

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

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.

Advantages of Wireless LANs

Great for allowing laptop computers or remote computers to connect to the Wireless LAN.
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,
They are susceptible to interference from lights and electronic devices.
They are also slower than LANs using cabling.

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