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The Physical Layer

This chapter explores the theoretical basis of data communication, including Fourier analysis, bandwidth-limited signals, and guided transmission data using twisted pair, coaxial cable, and fiber optics.

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The Physical Layer

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  1. The Physical Layer Chapter 2

  2. The Theoretical Basis for Data Communication • Fourier Analysis • Bandwidth-Limited Signals • Maximum Data Rate of a Channel

  3. Bandwidth-Limited Signals A binary signal and its root-mean-square Fourier amplitudes. (b) – (c) Successive approximations to the original signal.

  4. Bandwidth-Limited Signals (2) (d) – (e) Successive approximations to the original signal.

  5. Bandwidth-Limited Signals (3) Relation between data rate and harmonics.

  6. Guided Transmission Data • Magnetic Media • Twisted Pair • Coaxial Cable • Fiber Optics

  7. Twisted Pair (a) Category 3 UTP. (b) Category 5 UTP. Twisting done to stop cross-talk

  8. Coaxial Cable A coaxial cable.

  9. Fiber Optics (a) Three examples of a light ray from inside a silica fiber impinging on the air/silica boundary at different angles. (b) Light trapped by total internal reflection.

  10. Transmission of Light through Fiber Attenuation of light through fiber in the infrared region. Attenuation in decidels = 10 log_10 (transmitted power/received power)

  11. Fiber Cables (a) Side view of a single fiber. (b) End view of a sheath with three fibers. • Terminate in connector 15-20% LOSS • Spliced mechanically 10% loss • 3. Fused to form solid connection

  12. Fiber Cables (2) A comparison of semiconductor diodes and LEDs as light sources.

  13. Fiber Optic Networks A fiber optic ring with active repeaters.

  14. Fiber Optic Networks (2) A passive star connection in a fiber optics network.

  15. Advantages • Low attenuation, long lines – 50 km • Power surges, electromagnetic interference, power failure • Lightweight • Do not leak light, quite difficult to tap • Less familiar technology

  16. Class till here

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