Slide mạng máy tính nâng cao chapter2 the physical layer
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Chapter 2
The Physical Layer
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The Theoretical Basis for Data
Communication
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Fourier Analysis
Bandwidth-Limited Signals
Maximum Data Rate of a Channel
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Bandwidth-Limited Signals
A binary signal and its root-mean-square Fourier amplitudes.
(b) – (c) Successive approximations to the original signal.
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Bandwidth-Limited Signals (2)
(d) – (e) Successive approximations to the original signal.
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Bandwidth-Limited Signals (3)
Relation between data rate and harmonics.
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Guided Transmission Data
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Magnetic Media
Twisted Pair
Coaxial Cable
Fiber Optics
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Twisted Pair
(a) Category 3 UTP.
(b) Category 5 UTP.
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Coaxial Cable
A coaxial cable.
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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.
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Transmission of Light through Fiber
Attenuation of light through fiber in the infrared region.
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Fiber Cables
(a) Side view of a single fiber.
(b) End view of a sheath with three fibers.
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Fiber Cables (2)
A comparison of semiconductor diodes and LEDs as light sources.
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Fiber Optic Networks
A fiber optic ring with active repeaters.
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Fiber Optic Networks (2)
A passive star connection in a fiber optics network.
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Wireless Transmission
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The Electromagnetic Spectrum
Radio Transmission
Microwave Transmission
Infrared and Millimeter Waves
Lightwave Transmission
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The Electromagnetic Spectrum
The electromagnetic spectrum and its uses for communication.
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Radio Transmission
(a) In the VLF, LF, and MF bands, radio waves follow the
curvature of the earth.
(b) In the HF band, they bounce off the ionosphere.
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Politics of the Electromagnetic Spectrum
The ISM bands in the United States.
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Lightwave Transmission
Convection currents can interfere with laser communication systems.
A bidirectional system with two lasers is pictured here. 19
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Communication Satellites
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Geostationary Satellites
Medium-Earth Orbit Satellites
Low-Earth Orbit Satellites
Satellites versus Fiber
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Communication Satellites
Communication satellites and some of their properties,
including altitude above the earth, round-trip delay time
and number of satellites needed for global coverage. 21
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Communication Satellites (2)
The principal satellite bands.
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Communication Satellites (3)
VSATs using a hub.
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Low-Earth Orbit Satellites
Iridium
(a) The Iridium satellites from six necklaces around the earth.
(b) 1628 moving cells cover the earth.
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Globalstar
(a) Relaying in space.
(b) Relaying on the ground.
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