LAN Cabling

Types of Cabling:

The network cables are used to transmit the data signals from one computer to another. There are three types of cables used in PC networks.

• Co-axial cable
• Twisted – pair cable
• Fiber optic cable

a) Co-axial cable:

A coaxial cable consists of many small cables in a protective cover. The cover shields the cable from physical dangers as well as from electromagnetic interference. Within the cover, the various cables are shielded from interference with one another. Coaxial cables are used in communication networks that require many simultaneous communication links. Each coaxial cable can provide more than 5000 links.

There are two types of coaxial cables: baseband and broadband. A baseband coaxial cable transmits a single signal at a time at very high speed. A broadband coaxial cable can transmit many simultaneous signals using different frequencies. A baseband cable is mainly used for LANs. A broadband coaxial cable can carry only an analog signal. So it must be used with a modem.

Features:

•  It provides better immunity than twisted pair.
•  This cable is able to transmit data at higher rates.

Limitations:

•  High installation cost
•  High maintenance cost.

b) Twisted-Pair cable:

Twisted-pair cable is made up of pairs of copper wires twisted together in precisely calculated fashions. The wires carry more information when twisted. Two varieties of twisted-pair cable are,

• shielded twisted-pair cable
• Unshielded twisted-pair cable

1)Shielded twisted-pair cable:

Shielded twisted-pair cabling is more thoroughly insulated or shielded. This cabling is more reliable and expensive. It is easy to install. The twisted pair varies in quality and capacity. Quality and capacity depend upon the number of twists per inch and how much insulation it has. By twisting the wires around one another electromagnetic interference from external sources is reduced. By adding shielding, twisted pair is capable of transmitting data at higher rates.

2)Unshielded twisted pair cable:

In unshielded twisted pair cabling, the twisted pair cable is not shielded. Some organizations use existing telephone wiring for their LANs. This telephone wiring is usually unshielded twisted pair cable.

The main disadvantage associated with this is low noise immunity. During a telephone conversation, noise and interference from other electronic equipment takes the form of static and is rarely loud enough to disrupt the call.

But that same line can scramble a data transmission and require the sending device to retransmit. An excessive number of such retransmissions will reduce network efficiency.

Features of twisted-pair cables:

• Inexpensive
• Easy to install
• Easy to tap
• Can accommodate up to 1000 devices.

Limitations:

The network coverage area is between 300 feet and 1000 feet only.

c)  Fiber- optic cable:

A fiber-optic cable consists of strands of glass-like thread. Through the use of a laser, data are transmitted from one end of a cable to the other. Fiber optic cables will increase the capacity of like-sized coaxial cables by at least a factor of 10. This makes them valuable for use in a variety of applications mainly in communication network

Features:

• Huge bandwidth.
• Optical fiber systems are not affected by external noise.
• The error rate for the data transmitted across fiber optic cable is very low.

Limitations:

• Cost is high.
• Fibers fragility makes it more difficult to handle.