CBSE Class XIIth Computer Science Transmission Media -Shruti Mehra
Types of Transmission Media For any networking to be effective, raw stream of data is to be transported from one device to other over some medium. Various transmission media can be used for transfer of data. These transmission media may be of two types Guided In guided media, transmitted data travels through cabling system that has a fixed path. For example, copper wires, fibre opt c wires, etc. Unguided - In unguided media, transmitted data travels through free space in form of electromagne waves, lasers, etc. * tic signal. For example, radio Each transmission media has its own advantages and disadvantages in terms of bandwidth, speed, delay, cost per bit, ease of installation and maintenance, etc.
Twisted Pair Cable Copper wires are the most common wires used for transmitting signals because of good performance at lovw costs. They are most commonly used in telephone lines. However, if two or more wires are lying together, they can interfere with each other's signals. To reduce this electromagnetic interference, pair of copper wires are twisted together in helical shape like a DNA molecule. Such twisted copper wires are called twisted pair. To reduce interference between nearby twisted pairs, the twist rates are different for each pair. *
Advantages of twisted pair cable *Trained personnel easily availa learning curve * Can be used for both analog and digital transmissions * Least expensive for short distances * Entire network does not go down if a part of network is damaged Disadvantages of twisted pair cable * Signal cannot travel long distances without repeaters * High error rate for distances greater than 100m * Very thin and hence breaks easily Not suitable for broadband connections
Coaxial cables Coaxial cables are copper cables with better shielding than twisted pair cables, so that transmitted signals may travel longer distances at higher speeds. A coaxial cable consists of these layers, starting from the innermost * Stiff copper wire as core * Insulating material surrounding the core * Closely woven braided mesh of conducting material surrounding the insulator Protective plastic sheath encasing the wire Coaxial cables are widely used for cable TV connections and * LANs.
Advantages of Coaxial Cables Excellent noise immunity * Signals can travel longer distances at higher speeds, e.g. 1 to 2 Gbps for 1 Km cable * Can be used for both analog and digital signals * Inexpensive as compared to fibre optic cables * Easy to install and maintain Disadvantages of Coaxial Cables * Expensive as compared to twisted pair cables * Not compatible with twisted pair cables
Optical Fiber * Thin glass or plastic threads used to transmit data using light waves are called optical fibre. Light Emitting Diodes (LEDs) or Laser Diodes (LDs) emit light waves at the source, which is read by a detector at the other end. Optical fibre cable has a bundle of such threads or fibers bundled together in a protective covering. Each fibre is made up of these three layers, starting with the innermost layer * Core made of high quality silica glass or plastic *Cladding made of high quality silica glass or plastic, with a lower refractive index than the core Protective outer covering called buffer * * Note that both core and cladding are made of similar material. However, as refractive index of the cladding is lower, any stray light wave trying to escape the core is reflected back due to total internal reflection.
Advantages of Optical Fibre Optical fibre is fast replacing copper wires because of these advantages that it offers- * High bandwidth Immune to electromagnetic interference * Suitable for industrial and noisy areas * Signals carrying data can travel long distances without weakening Disadvantages of Optical Fibre * Optical fibre cables are expensive Sophisticated technology required for manufacturing, installing and maintaining optical fibre cables Light waves are unidirectional, so two frequencies are required for full duplex transmission
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