For making LANs various types of cables are used. The type of cable depends on size of network and distance between computers. It also depends on the data rate requirement of the network. Normally the networks use either twisted pair cables or coaxial cables. The fiber optic networks used fiber optic cables. The wireless LANs do not use cables rather they depend on satellite communications or wireless frequencies. Thus the cables used for networking may be categorized as twisted pair cables, coaxial cables and optical fiber cables.
Twisted Pair Cables: - in this type of cable pair of wires are twisted together. They are insulated from each other. One is used for signal and other for ground reference. Some times multiple twisted pairs are enclosed within the same cable. It reduces the crosstalk. They are suitable for bit rates of the order of 1 Mbps over short distances i.e. less than 100m. With lower bit rates they can be used for larger distances reliably. If driver and receiver circuits used are more sophisticated then they can be used for higher bit rates and larger distances.
Two types of twisted pair cable are unshielded twisted pair (UTP) and shielded twisted pair (STP). UTP are used in telephone networks and in other data communication equipments. UTP are the most widely used cables in local area network. They are available in various categories and marked as CAT1, CAT2 etc. STP is used with protective screen or shield to reduce effect of interference of signal. The major drawback of these types of cables is skin effect and their limited capacity.
Coaxial Cable: - In a coaxial cable there is a central conductor covered with insulating material. Over this insulator the second braided conductor is present which is covered with other insulator cover. The major problems of high attenuation and signal power loss at high frequencies of twisted pair cables were minimized by using coaxial cables. In this the signal and ground reference wire minimized by using coaxial cables in circular conductor. The space between two conductors is filled with dielectric insulation material with a honey comb. The skin effect and power losses were minimized by these cables. They can be used with number of different signal types.
Fiber optic Cables: - The fiber optical differ from metallic cables i.e. coaxial cables and twisted pair cables in the sense that it carries the transmitted information in form of fluctuating beam of light in a glass fiber instead of an electrical signal on a wire. They can achieve transmission rates of hundreds of megabits per second because of the wider bandwidth of light waves. Light waves are immune to electromagnetic interference and crosstalk. These cables are extremely useful for the transmission or power bit rate signals in electrically noisy environments. They can not be tapped physically so they are used at places where security is required. It consists of a single glass fiver for each signal to be transmitted. These fibers are places in a protective coating which shields the fiver from external light source. An optical transmitter and optical receiver are used at ends. The transmitter uses light-emitting diode (LED) or laser diode (LD) to perform conversion operation.
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