Transcript Module 1.0: Introduction

Module 3.2: Transmission Media
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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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Electromagnetic Spectrum
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Guided Transmission Media
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Twisted Pair
Coaxial cable
Optical fiber
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Twisted Pair
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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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Unshielded and Shielded TP
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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 10-155 Mbps
UTP Categories
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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
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RJ-11 is a typical UTP phone
connector. Has 2 pairs.
RJ-45 is a UTP connector.
Has 4 pairs.
Coaxial Cable
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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
Transmission Characteristics
 Analog
 Amplifiers every few km
 Closer if higher frequency
 Up to 500MHz
 Digital
 Repeater every 1km
 Closer for higher data rates
Short distance computer
systems links
Local area networks
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Optical Fiber
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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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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.
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MMF vs. SMF
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Comparison
Cable Type
Cost
1 = lowest
5 = highest
Typical
Capacity
Installation
1 = easy
5 = hard
Max Cable
Length
EMI
Resistance
1 = low
5 = high
CoaxialThinnet
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10 Mbps
2
185 meters
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CoaxialThicknet
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10 Mbps
3
500 meters
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UTP
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10-100 Mbps
1
100 meters
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STP
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16-155 Mbps
2
100 meters
2
Fiber-optic
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100+ Mbps
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Multiple
kilometers
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Wireless Transmission
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Unguided media
Frequencies
Transmission and reception
via antenna
Directional
– Focused beam
– Careful alignment
required
Omnidirectional
– Signal spreads in all
directions
– Can be received by many
antennae
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 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
Types of Radio Propagation
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Microwave
Satellite Microwave
Terrestrial Microwave
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 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
Parabolic dish
Focused beam
Line of sight
Long haul
telecommunications
Higher frequencies give
higher data rates
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Wide Area: Satellite Systems
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Cover very large areas
Different orbit heights
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GEOs (39000 Km), LEOs
(2000 Km), MEOs (9000km)
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GEO is stationary. You need 3 to cover
whole planet
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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
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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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LEO and MEO
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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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WLAN
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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 802.11b operates at 2.4 GHz range and gives 11Mbps
– IEEE 802.11a operates at 5 GHz range and gives 54Mbps
– IEEE 802.11g 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 2.4 - 2.4835 GHz
– May have interference with Ethernet WLAN APs
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Others
IR (Infrared)
 Modulate noncoherent
infrared light
 Line of sight (or reflection)
 Blocked by walls
 e.g. TV remote control,
IRD port
Broadcast Radio
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Omnidirectional
FM radio
UHF and VHF television
Line of sight
Suffers from multipath
interference
– Reflections
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Cellular System
Cellular Bands
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