Network Cables : UTP, STP, Fiber Cable and Co-axial Cable

Cable is the medium of transferring information form one network devices to another network device There are different types of cable which are commonly used in local area network (LAN). The choice of cable depends on the topology, protocols and size of the network. Let us understand the characteristics of the different type of cables and where they are used.

The types of cables used in networks are:

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

Unshielded Twisted Pair (UTP)

The quality of UTP may vary according to the category of cable pair used. 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 cable categories according to their speed.

Categories of UTP

Category	Speed	Uses
1	1 Mbps	Voice Only (used in telephone wire)
2	4 Mbps	Telephone wire
3	16 Mbps	10 Base-T Ethernet
4	20 Mbps	Token Ring
5	100 Mbps	100 Base-T Ethernet
5e	1 Gbps	GB Ethernet

Unshielded Twisted Pair (UTP) Connector:

The standard connector for UTP is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector as shown in figure below. A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard defined in the telephone industry. These standards also define the how each pin should connect inside the connector.

Fig.1: RJ-45 Connector

Shielded Twisted Pair (STP) Connector:

Although UTP cable is the least expensive cable, it is susceptible to radio and electrical frequency interference caused due to other electrics equipment present near the cable. If you must place cable in environments with lots of potential interference, or 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:

1. Each pair of wires is individually shielded with foil.

2. There is a foil or braid shield inside the jacket covering all wires (as a group).

3. There is a shield around each individual pair, as well as around the entire group of wires (referred to as double shield twisted pair).

The twisted-pair cable was primarily developed for computer networks. This cable is also known as Ethernet cable. Almost all modern LAN computer networks use this cable.

Coaxial Cable:

Coaxial cabling has a single copper conductor at its centre. A plastic layer provides insulation between the centre conductor and a braided metal shield as shown in the figure below. The metal shield helps to block any outside interference caused from fluorescent lights, motors, and other computers.

Fig.2: Co-axial 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 thin-net. 10 Base-2 refers to the specifications for thin coaxial cable carrying Ethernet signals. Here, 2 refers to the approximate maximum segment length being 200 meters. In actual, the maximum segment length is around 185 meters. Thin coaxial cable types are very popular in school networks, especially when the topology is of linear bus networks type.

Thick coaxial cable is also referred to as thick-net. 10 Base-5 refers to the specifications for thick coaxial cable carrying Ethernet signals. Here, 5 refers to the maximum segment length being around 500 meters. Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the centre 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 it is difficult to install.

Fig.3: Categorize of co-axial cable based on Applications.

Coaxial Cable Connector:

The most common type of connector used with coaxial cables is the Bayone-Neill-Concelman (BNC) connector. There are different types of adapters are available for BNC connectors which includes a T-connector, barrel connector, and terminator. Connectors on the cable are the weakest points in any network. BNC connector of crimp type rather than screw type is used to avoid network connection problem.

Fig.4: BNC Connector with wire.

Fibre Optical Cable:

Fiber optic cable consists of a centre 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.

Fig.5: Fiber Optical Cable

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. 10 Base-F refers to the specifications for fiber optic cable carrying Ethernet signals.

The centre core of fiber cables is made from glass or plastic fibres (see figure below). A plastic coating then cushions the fiber centre, and kevlar fibre help to strengthen the cables and prevent breakage. The outer insulating jacket made of Teflon or PVC.

Fig.6: Fiber optic cable

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.

Specification	Cable Type
10 Base-T	Unshielded Twisted Pair
10 Base-2	Thin Coaxial
10 Base-5	Thick Coaxial
100 Base-T	Unshielded Twisted Pair
100 Base-FX	Fiber Optic
100 Base-BX	Single mode Fiber
100 Base-SX	Multimode Fiber
1000 Base-T	Unshielded Twisted Pair
1000 Base-FX	Fiber Optic
1000 Base-BX	Single mode Fiber
1000 Base-SX	Multimode Fiber