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Data and Computer Communications Chapter 4
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Data and Computer Communications Chapter 4
Transmission Media
- Design Factors
- bandwidth
- transmission impairments
- interference
- number of receivers in guided media
- Electromagnetic Spectrum
- Transmission Characteristics of Guided Media
- Twisted pair
- Twisted pairs
- analog
- digital
- limited distance
- limited bandwidth
- susceptible to interference and noise
- limited data rate
- Coaxial cable
- Coaxial Cable - Transmission Characteristics
- superior frequency
- analog signals
- digital signals
- performance limited by attenuation & noise
- Coaxial Cable - Transmission Characteristics
- Optical fiber
- Optical Fiber - Benefits
- greater capacity
- smaller size & weight
- lower attenuation
- electromagnetic isolation
- greater repeater spacing
- Optical Fiber - Transmission Characteristics
- uses total internal reflection to transmit light
- can use several different light sources
- relation of wavelength, type & data rate
- can use several different light sources
- uses total internal reflection to transmit light
- Optical Fiber - Benefits
- Unshielded vs Shielded TP
- unshielded Twisted Pair (UTP)
- shielded Twisted Pair (STP)
- Near End Crosstalk
- coupling of signal from one pair to another
- occurs when transmit signal entering the link
- near transmitted signal is picked up by near receiving pair
- Wireless Transmission Frequencies
- 2GHz to 40GHz
- 30MHz to 1GHz
- 3 x 10^11 to 2 x 10^14
- Antennas
- electrical conductor used to radiate or collect electromagnetic energy
- transmission antenna
- reception antenna
- same antenna is often used for both purposes
- Antenna Gain
- measure of directionality of antenna
- power output in particular direction verses that produced by an isotropic antenna
- measured in decibels (dB )
- results in loss in power in another direction
- effective area relates to size and shape
- Radiation Pattern
- power radiated in all directions
- not same performance in all directions
- an isotropic antenna is a (theoretical) point in space
- Terrestrial Microwave
- used for long haul telecommunications
- requires fewer repeaters but line of sight
- use a parabolic dish to focus a narrow beam onto a receiver antenna
- 1-40GHz frequencies
- use a parabolic dish to focus a narrow beam onto a receiver antenna
- requires fewer repeaters but line of sight
- and short point-to-point links
- higher frequencies give higher data rates
- main source of loss is attenuation
- also interference
- used for long haul telecommunications
- Satellite Microwave
- satellite is relay station
- receives on one frequency, amplifies or repeats signal and transmits on another frequency
- typical uses
- typically requires geo-stationary orbit
- Broadcast Radio
- radio is 3kHz to 300GHz
- use broadcast radio, 30MHz - 1GHz
- is omnidirectiona
- still need line of sight
- suffers from multipath interference
- Infrared
- modulate noncoherent infrared light
- end line of sight (or reflection)
- are blocked by walls
- no licenses required
- typical uses
- Refraction
- velocity of electromagnetic wave is a function of density of materia
- speed changes as move between media
- Index of refraction (refractive index
- have gradual bending if medium density varies
- Line of Sight Transmission
- Free space loss
- Atmospheric Absorption
- Multipath
- Refraction
- Design Factors
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- Mapa Mental sobre Data and Computer Communications Chapter 4, creado por J H el 02/11/2021.
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- J H
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