Chapter 7:
Transmission Media
Abdullah Konak
School of Information Sciences and Technology
Penn State Berks
Learning Objectives
„ Describe and be familiar the various
transmission media
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Transmission Media
Media
Guided Media
Twisted Pair
Unguided Media
Coaxial
Shielded
Baseband
Unshielded
Broadband
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Optical Fiber
Radio
Microwaves
Terrestrial
Microwave
Infrared
Satellite
Microwave
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Twisted Pair
Source of Interference (Electromagnetic waves)
Noise on the cable,
created by the other
devices.
Noise on each
cable cancels
(evens) each
other out at
the end.
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Twisted Pair Types: UTP and STP
Unshielded
Twisted Pair
(UTP)
Jacket/sheath
Shielded
Twisted Pair
(STP)
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Category 3 (CAT3) and CAT5
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Straight-Through CAT 5 with RJ-45
Connectors
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Crossover Cable CAT 5 with RJ-45
Connectors
A straight-thru cable has identical ends.
A crossover cable has different ends.
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Coaxial Cable (Coax)
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Baseband vs Broadband Coax
Baseband
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Broadband
Unmodulated digital signal.
Single channel.
Bidirectional propagation of signal.
Stations connected via T
connectors.
No need of modems - low cost
installation.
ADVANTAGES:
Simplicity
Low cost
Ease of installation and
maintenance
High rates
DISADVANTAGES:
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Limited distances
Data and voice only
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Digital signal modulated onto RF
carrier (analog).
Channel allocation based on FDM.
Head-End for bidirectional
transmission.
Stations connected via RF modems.
ADVANTAGES:
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Data, voice and video
Greater distances
Greater bandwidth
DISADVANTAGES:
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Cable design
Alignment and maintenance
High cost, requires modems
Lack of well developed standards
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Fiber Optic
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Guided Transmission Media
Performance
Medium
Cost
Throughput Attenuation
Interference Security
UTP
Low
Up to 100
Mbps
High
High
Low
STP
Moderate
Up to 150
Mbps
High
Moderate
Low
Coaxial
Moderate
Up to 1
Gbps
Moderate
Moderate
Low
Optical
Fiber
High
Up to 2
Gbps
Low
Low
High
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Unguided Medium
microwave and infrared are
suitable for point-to-point
transmission
radio waves are
omnidirectional
The smaller the wavelength (the higher frequency),
the more suitable waves for point-to-point transmission
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Radio Waves: 100,000 km (3Hz) to 30cm (1GHz).
Microwaves: 30 cm (1 GHz) to 1cm (30 GHz).
Infrared: 1 mm (300 GHz) to 750 μ m (400 THz).
Laser (future)
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Electromagnetic Radio Waves
Spectrum in Telecommunications
Band
Frequency
Common Uses
Very Low Frequency (VLF)
10 kHz to 30 kHz
Marine-time ship-to-shore
Low Frequency (LF)
30 kHz to 300 kHz
Cordless phones
Medium Frequency (MF)
300 kHz to 3 MHz
AM Radio
High Frequency (HF)
3 MHz to 30 MHz
Shortwave radio, CB radio
Very High Frequency (VHF)
30 MHz to 144 MHz
144 MHz to 174 MHz
174 MHz to 328.6 MHz
TV Stations 2-6, FM radio
Taxi Stations
TV Stations 7-13
Ultra High Frequency (UHF)
328.6 MHz to 450 MHz
450 MHz to 470 MHz
470 MHz to 806 MHz
806 MHz to 960 MHz
960 MHz to 2.3 GHz
2.3 GHz to 2.9 GHz
Public safety
Cellular and PCS phones
Pagers
PCS phones
Air traffic control radar
WLAN (802.11b)
Super High Frequency (SHF)
2.9 GHz to 30 GHz
WLAN(802.11a)
Extremely High Frequency (EHF)
30 GHz and above
high-speed microwave data links
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Examples
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AM radio - 535 KHz to 1.7 MHz
Television stations - 54 to 88 MHz for channels 2 through 6
FM radio - 88 MHz to 108 Mhz
Television stations - 174 to 220 Mhz for channels 7 through
Garage door openers, alarm systems, etc. - Around 40 Mhz
Standard cordless phones: Bands from 40 to 50 Mhz
Baby monitors: 49 Mhz
Radio controlled airplanes: Around 72 megahertz, which is different from...
Radio controlled cars: Around 75 megahertz
Wildlife tracking collars: 215 to 220 megahertz
MIR space station: 145 megahertz and 437 megahertz
Cell phones: 824 to 849 megahertz
New 900-MHz cordless phones: Obviously around 900 megahertz!
Air traffic control radar: 960 to 1,215 megahertz
Global Positioning System: 1,227 and 1,575 megahertz
Deep space radio communications: 2290 megahertz to 2300 megahertz
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Terrestrial Microwave
„ Land based, line-of-sight transmissions
„ Antenna: parabolic "dish“, 3 meters in
diameters.
„ Maximum 20-30 miles between towers
„ High data rates
„ Used by telephone companies and businessto-business transmission
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Terrestrial Microwave Antennaes
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Problems
„ Attenuation increases with rainfall, especially
above 10GHz.
„ Overlapping transmission areas (frequency
band control is necessary)
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Satellite
Microwave Transmission
„ a microwave relay station in space
„ can relay signals over long distances
„ geostationary satellites
remain above the equator at a height of
22,300 miles (geosynchronous (GEO) orbit)
„ travel around the earth in exactly the time the
earth takes to rotate
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Satellite Positions
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Satellite Transmission Process
satellite
transponder
dish
dish
22,300 miles
uplink station
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downlink station
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Infrared
„ Uses transmitters/receivers (transceivers)
that modulate noncoherent infrared light.
„ Transceivers must be within line of sight of
each other (directly or via reflection ).
„ Unlike microwaves, infrared does not
penetrate walls.
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