Chapter 4 Transmission Media

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William Stallings

Data and Computer

Communications

Chapter 4

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Overview

 _{Guided - wire}

 _{Unguided - wireless}

 _{Characteristics and quality determined by}

medium and signal

 _{For guided, the medium is more important}  _{For unguided, the bandwidth produced by}

the antenna is more important

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Design Factors

 _Bandwidth

 _{Higher bandwidth gives higher data rate}  _{Transmission impairments}

 _Attenuation  _Interference

 _{Number of receivers}  _{In guided media}

 _{More receivers (multi-point) introduce}

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Guided Transmission Media

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Twisted Pair - Applications

 _{Most common medium}

 _{Telephone network}

 _{Between house and local exchange}

(subscriber loop)

 _{Within buildings}

 _{To private branch exchange (PBX)}  _{For local area networks (LAN)}

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Twisted Pair - Pros and Cons

 _Cheap

 _{Easy to work with}  _{Low data rate}

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Twisted Pair - Transmission

Characteristics

 _Analog

 _{Amplifiers every 5km to 6km}  _Digital

 _{Use either analog or digital signals}  _{repeater every 2km or 3km}

 _{Limited distance}

 _{Limited bandwidth (1MHz)}  _{Limited data rate (100MHz)}

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Unshielded and Shielded TP

 _{Unshielded Twisted Pair (UTP)}  _{Ordinary telephone wire}

 _Cheapest

 _{Easiest to install}

 _{Suffers from external EM interference}  _{Shielded Twisted Pair (STP)}

 _{Metal braid or sheathing that reduces}

interference

 _{More expensive}

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UTP Categories

 _{Cat 3}

 _{up to 16MHz}

 _{Voice grade found in most offices}  _{Twist length of 7.5 cm to 10 cm}  _{Cat 4}

 _{up to 20 MHz}  _{Cat 5}

 _{up to 100MHz}

 _{Commonly pre-installed in new office}

buildings

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Near End Crosstalk

 _{Coupling of signal from one pair to}

another

 _{Coupling takes place when transmit signal}

entering the link couples back to receiving pair

 _{i.e. near transmitted signal is picked up by}

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Coaxial Cable Applications

 _{Most versatile medium}  _{Television distribution}

 _{Ariel to TV}  _{Cable TV}

 _{Long distance telephone transmission}  _{Can carry 10,000 voice calls}

simultaneously

 _{Being replaced by fiber optic}

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Coaxial Cable - Transmission

Characteristics

 _Analog

 _{Amplifiers every few km}  _{Closer if higher frequency}  _{Up to 500MHz}

 _Digital

 _{Repeater every 1km}

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Optical Fiber - Benefits

 _{Greater capacity}

 _{Data rates of hundreds of Gbps}  _{Smaller size & weight}

 _{Lower attenuation}

 _{Electromagnetic isolation}  _{Greater repeater spacing}

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Optical Fiber - Applications

 _{Long-haul trunks}

 _{Metropolitan trunks}

 _{Rural exchange trunks}  _{Subscriber loops}

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Optical Fiber - Transmission

Characteristics

 _{Act as wave guide for 10}14 to 1015 Hz

 _{Portions of infrared and visible spectrum}  _{Light Emitting Diode (LED)}

 _Cheaper

 _{Wider operating temp range}  _{Last longer}

 _{Injection Laser Diode (ILD)}  _{More efficient}

 _{Greater data rate}

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Wireless Transmission

 _{Unguided media}

 _{Transmission and reception via antenna}  _Directional

 _{Focused beam}

 _{Careful alignment required}  _{Omnidirectional}

 _{Signal spreads in all directions}

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Frequencies

 _{2GHz to 40GHz}

 _Microwave

 _{Highly directional}  _{Point to point}

 _Satellite

 _{30MHz to 1GHz}

 _{Omnidirectional}  _{Broadcast radio}  _{3 x 10}11 to 2 x 1014

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Terrestrial Microwave

 _{Parabolic dish}

 _{Focused beam}

 _{Line of sight}

 _{Long haul telecommunications}

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Satellite Microwave

 _{Satellite is relay station}

 _{Satellite receives on one frequency,}

amplifies or repeats signal and transmits on another frequency

 _{Requires geo-stationary orbit}  _{Height of 35,784km}

 _Television

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Broadcast Radio

 _{Omnidirectional}  _{FM radio}

 _{UHF and VHF television}  _{Line of sight}

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Infrared

 _{Modulate noncoherent infrared light}  _{Line of sight (or reflection)}

 _{Blocked by walls}

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Required Reading