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Transmission Media

Lesson 04

NETS2150/2850

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Lesson Outline

Wired or guided Media– Electromagnetics waves are guided along

a solid medium Wireless or unguided media

– Transmission occurs through atmosphere, outer space or water

Understand media characteristics and typical applications

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Classes of transmission media

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Electromagnetic Spectrum

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Twisted-pair cable

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Note:

Single pair represents one communication link

Twisting reduces crosstalk interference between pairs

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UTP and STP

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Categories of unshielded twisted-pair cablesCategories of unshielded twisted-pair cables

Category Bandwidth Data Rate Digital/Analog Use

3 very low < 100 kbps Analogue Telephone

4 20 MHz 20 Mbps Digital LANs

5 100 MHz 100 Mbps Digital LANs

6 200 MHz 200 Mbps DigitalHigh-speed

LANs

7 600 MHz 600 Mbps DigitalHigh-speed

LANs

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UTP connector

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Twisted Pair - Applications

Most common medium Unshielded Twisted Pair (UTP)

– Cheapest– Easiest to install– Voice Grade: Telephone wire (Cat 3)– Data Grade: Better quality (Cat 5)

• For LAN, 100 Mbps over 100 m possible

Shielded Twisted Pair (STP)– Metal braid reduces interference– More expensive– Harder to handle (thick, heavy)

U T P S TP

T w is te d P a ir

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Coaxial Cable

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Coaxial Cable Applications

Most versatile medium Television distribution

– Arial to TV– Cable TV

Short distance computer systems links Local area networks

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Bending of light ray for transmission

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Optical Fibre

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Figure 7.12 Propagation modes

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Figure 7.13 Modes

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Optical Fibre - Benefits Great for “noisy”

environments! Tremendous bandwidth

– Data rates of hundreds of Gbps

Smaller size & weight Lower attenuation

– Greater amplifier spacing– 40-60 km at least before amplification required for SMF

Used in backbone and high traffic inter-city or inter continent links (submarine cables - undersea)

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Wireless transmission waves

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Wireless SpectrumWireless Spectrum

BandBand RangeRange PropagationPropagation ApplicationApplication

VLFVLF 3–30 KHz Ground Long-range radio navigation

LFLF 30–300 KHz GroundRadio beacons and

navigational locators

MFMF 300 KHz–3 MHz Sky AM radio

HF HF 3–30 MHz SkyCitizens band (CB),

ship/aircraft communication

VHF VHF 30–300 MHzSky and

line-of-sightVHF TV, FM radio

UHF UHF 300 MHz–3 GHz Line-of-sightUHF TV, cellular phones,

paging, satellite

SHF SHF 3–30 GHz Line-of-sight Satellite communication

EHFEHF 30–300 GHz Line-of-sight Long-range radio navigation

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Wireless Transmission

30MHz to 1GHz– Suitable for Omnidirectional– Broadcast radio

2GHz to 40GHz– Microwave range– Highly directional– Point to point

3 x 1011 to 2 x 1014 Hz– Infrared range– Used within confined areas

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Broadcast Radio

Omnidirectional FM radio UHF and VHF

television Requires line of sight

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Omnidirectional antennas

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Radio waves are used for broadcast communications, such as radio and

television, and paging systems.

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Terrestrial Microwave

Uses parabolic dish as antenna

Focused beam Requires line of sight Used for mobile phones, satellite

networks Higher frequencies give higher data

rates

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Line of Sight Propagation

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Satellite Microwave

Satellite is a relay station It receives on one frequency (uplink),

amplifies or repeats signal and transmits on another frequency (downlink)

Requires geo-stationary orbit– Height of 35,863 km

Applications:– Television live cast– Long distance telephone– Private business networks

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Satellite Point to Point Link

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Satellite Broadcast Link

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Primary Mission: Four-year tour to study Saturn, its rings, moons and magnetosphere Launch: 15 October 1997 from Cape Canaveral Air Force Station, Florida Arrival at Saturn: 1 July 2004 Distance Travelled: 3.5 billion km

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Infrared

Line of sight (or reflection) Shirt-range communications Blocked by walls e.g. TV remote control, infrared port on

printers, laptops, mobile phones, PDAs etc.

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Summary Guide Media

– Twisted pair, Coaxial cable, Optical fibre Unguided or wireless media

– Uses antenna as transmitter and receiver (transceiver)

– Terrestrial microwave, satellite microwave, Broadcast radio, Infrared

Characteristics and quality determined by medium and signal

For guided transmission, the medium is more important

For unguided, the bandwidth produced by the antenna is more important