1. Module 3.2: Transmission Media
Electromagnetic Spectrum
Guided Transmission Media
Twisted Pair
Coaxial cable
Optical fiber
Unguided Transmission Media
Terrestrial Microwave
Satellite
Radio IR
Cellular Telephony
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2. Electromagnetic Spectrum
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3. Guided Transmission Media
Twisted Pair
Coaxial cable
Optical fiber
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4. Twisted Pair Most common medium Telephone network
Between house and local exchange (subscriber loop)
Within buildings
To private branch exchange (PBX)
For local area networks (LAN)
10Mbps or 100Mbps
Pros and Cons:
Cheap
Easy to work with
Low data rate
Short range, about 100 meters.
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5. 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
Harder to handle (thick, heavy)
Capacity Mbps
UTP Categories
Cat 3
up to 16MHz
Voice grade found in most offices
Cat 4
up to 20 MHz
Cat 5
up to 100MHz
Commonly pre-installed in new office buildings
RJ-11 vs. RJ-45
RJ-11 is a typical UTP phone connector. Has 2 pairs.
RJ-45 is a UTP connector. Has 4 pairs.
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6. Transmission Characteristics
Coaxial Cable
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
Short distance computer systems links
Local area networks
Transmission Characteristics
Analog
Amplifiers every few km
Closer if higher frequency
Up to 500MHz
Digital
Repeater every 1km
Closer for higher data rates
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7. Optical Fiber Greater capacity Data rates of hundreds of Gbps
Smaller size & weight
Lower attenuation
Electromagnetic isolation
Greater repeater spacing
10s of km at least
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8. Transmission Characteristics
Act as wave guide for 1014 to 1015 Hz
Portions of infrared and visible spectrum
Light Emitting Diode (LED) used in MMF
Cheaper
Wider operating temp range
Last longer
Injection Laser Diode (ILD) used in SMF
More efficient
Greater data rate
Wavelength Division Multiplexing (WDM) using light prisms.
MMF vs. SMF
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9. Comparison Cable Type Cost 1 = lowest 5 = highest Typical Capacity
Installation
1 = easy
5 = hard
Max Cable Length
EMI Resistance
1 = low
5 = high
Coaxial-Thinnet 2
10 Mbps
185 meters
Coaxial-Thicknet 4 3
500 meters
UTP 1
Mbps
100 meters
STP
Mbps
Fiber-optic 5
100+ Mbps
Multiple kilometers
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10. Wireless Transmission
Unguided media
Transmission and reception via antenna
Directional
Focused beam
Careful alignment required
Omnidirectional
Signal spreads in all directions
Can be received by many antennae
Frequencies
2GHz to 40GHz
Microwave
Highly directional
Point to point
Satellite
30MHz to 1GHz
Omnidirectional
Broadcast radio
3 x 1011 to 2 x 1014
Infrared
Local pt-pt confined area
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11. Types of Radio Propagation
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12. Terrestrial Microwave
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
GEO vs. LEO
Frequency Bands: C, Ku, and Ka
Television
Long distance telephone
Private business networks
Terrestrial Microwave
Parabolic dish
Focused beam
Line of sight
Long haul telecommunications
Higher frequencies give higher data rates
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13. Wide Area: Satellite Systems
Cover very large areas
Different orbit heights
GEOs (39000 Km), LEOs
(2000 Km), MEOs (9000km)
GEO is stationary. You need 3 to cover
whole planet
LEO and MEO orbit the earth every one hour
Dish antennas, or bulky handsets
Optimized for one-way transmission,
location positioning, GPS systems, Satellite Radio
Radio (XM, DAB) and movie (SatTV) broadcasting
Killed MMDS wireless TV offerings.
Future: satTV (eg: directTV) in your car
Most two-way systems struggling or bankrupt
Expensive alternative to terrestrial cellular system (2G)
Trucking fleets, journalists in wild areas, Oil rigs
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14. LEO and MEO Used in GPS 24 MEOs are need to cover the whole planet
54 for LEOs to cover the whole planet
Could have multiple readings for increased precision and reliability.
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15. WLAN Benefits of Ethernet WLAN Cheap Faster to deploy Mobility
Watch for security
Need for authentication
Need for encryption during transmission
What is an Access Point?
A typical diameter is a room for one AP about 40 meters
Frequencies used and data rate
IEEE b operates at 2.4 GHz range and gives 11Mbps
IEEE a operates at 5 GHz range and gives 54Mbps
IEEE g operates at 2.4 GHz range and gives 54Mbps
Bluetooth gives 1Mbps. Bluetooth networks PDAs or cell phones with PCs. Operates in a short diameter (10 meters).
Operates at GHz
May have interference with Ethernet WLAN APs
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16. Others IR (Infrared) Broadcast Radio
Modulate noncoherent infrared light
Line of sight (or reflection)
Blocked by walls
e.g. TV remote control, IRD port
Broadcast Radio
Omnidirectional
FM radio
UHF and VHF television
Line of sight
Suffers from multipath interference
Reflections
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17. Cellular System
Cellular Bands
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