guided media

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  • 1. Guided MediaGuided media, which are those that provide aconduit from one device to another, includetwisted-pair cable, coaxial cable, and fiber-opticcable.

2. Guided media 3. Twisted-Pair CableA twisted pair consists of two conductors (normally copper), each withits own plastic insulation, twisted together.One of the wires is used to carry signals to the receiver, and the otheris used only as a ground reference. The receiver uses the differencebetween the two.In addition to the signal sent by the sender on one of the wires,interference (noise) and crosstalk may affect both wires and createunwanted signals. 4. Figure 7.3 Twisted-pair cable 5. UTP and STP cables 6. Applications Twisted-pair cables are used in telephone lines toprovide voice and data channels. The local loop-the line that connects subscribers to thecentral telephone office ---commonly consists ofunshielded twisted-pair cables. The DSL lines that are used by the telephone companiesto provide high-data-rate connections also use thehigh-bandwidth capability of unshielded twisted-paircables. 7. Coaxial CableCoaxial cable carries signals of higher frequency ranges thanthose in twisted pair cable, in part because the two media areconstructed quite differently. Instead of having two wires, coaxhas a central core conductor of solid or stranded wire.The outer metallic wrapping serves both as a shield againstnoise and as the second conductor, which completes the circuit. 8. Coaxial cable 9. Coaxial Cable ConnectorsTo connect coaxial cable to devices, we need coaxialconnectors.The most common type of connector used today is the Bayone-Neill-Concelman (BNe), connector. Figure shows three populartypes of these connectors: the BNC connector, the BNC Tconnector, and the BNC terminator. 10. BNC connectors 11. Fiber-Optic CableA fiber-optic cable is made of glass or plastic and transmitssignals in the form of light.To understand optical fiber, we first need to explore severalaspects of the nature of light.Light travels in a straight line as long as it is movingthrough a single uniform substance.If a ray of light traveling through one substance suddenlyenters another substance the ray changes direction. 12. Fiber optics: Bending of light ray 13. Propagation ModesTwo modes (multimode and single mode)for propagating light along optical channels,each requiring fiber with different physicalcharacteristics. Multimode can beimplemented in two forms: step-index orgraded-index 14. Optical fiber 15. Fiber construction 16. Advantages Higher bandwidth Immunity to electromagnetic interference Resistance to corrosive materials Lightweight Less signal attenuation. 17. Disadvantages Installation and maintenance Unidirectional light propagation Cost

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