Ch7_1_TransmissionMedia
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Transcript Ch7_1_TransmissionMedia
Transmission Media
1
Transmission Media
Background
Guided Media
Unguided Media
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Transmission Media
Electromagnetic Spectrum
Visible light, 430-750
THz
Power,
voice
0
Radio communication Radio, Infrared
microwave, satellite
light
3KHz
Ultraviolet
light
X. Gamma,
cosmic rays
300 GHz
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Transmission Media :
Background
Communication signals are transmitted from
one device to another in the form of
electromagnetic energy
They can travel through a vacuum, air or
other transmission media
Transmission media are divided into two
categories
– Guided
– unguided
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Guided Media
Guided Media
Twisted pair
cable
Unshielded
Twisted pair
Coaxial
cable
Fiber-optic
cable
Shielded
Twisted pair
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Twisted-Pair Cable
Frequency Range for Twisted-pair cable
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Unshielded Twisted Pair (UTP)
Cable
Common type of telecommunication
medium in use today
Its frequency range is suitable for
transmitting both data and voice
Cheap
Flexible and easy to install
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UTP
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UTP Categories
5 EIA categories (CAT1-5)
1 lowest quality, 5 highest quality
CAT1
– Basic twisted pair, used in telephone system
– Quality is fine for voice
Not enough for data communication
(Low speed)
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UTP Categories
CAT2
– Suitable for voice and data communication
– Speed is up to 4 Mbps
CAT3
– Required to have at least 3 twist per foot
– Some other requirements
– Transmission rate up to 10 Mbps
CAT4
– Similar requirement as CAT3
– Transmission rate up to 16 Mbps
CAT5
– Transmission rate up to 100 Mbps
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UTP Connector
The most frequently used is an RJ45
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Shielded Twisted Pair (STP)
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Coaxial Cable
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Optical Fiber
Glass/plastic
Transmits signal in form of light
Nature of light
– Fastest speed in vacuum
300,000 km/sec
– Refraction
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Optical Fiber
Optical fiber uses reflection to guide light
through a channel
A glass or a plastic core is surrounded by a
cladding of less dense glass or plastic
Information is encoded onto a beam of light
as a series of on-off flashes that represents
1 and 0 bits
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Propagation Modes
Current technology supports two form for
propagating light along optical channel
– Multimode
– Single mode
Multimode
– Multiple beams move through the core in
different paths
Single Mode
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Multimode
Multimode Step-Index
Multimode Graded-Index
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Single Mode
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Fiber Construction
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Fiber Sizes
Defined by the ratio of
diameter of the core to
the diameter of the
cladding (micrometers)
Common sizes are
Fiber Type
62.5/12.5
Core (microns) Cladding (microns)
62.5
12.5
50/12.5
100/140
8.3/12.5
50
100
8.3
12.5
140
12.5
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Fiber Optic Advantages
Noise resistance
– Noise is not a factor to light
– External light is blocked from the channel by the
outer jacket
Less signal attenuation
– Transmission distance is greater than other
media
– A signal can run for a long distance without
requiring regeneration
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Fiber Optic Advantages
Higher Bandwidth
– Supports higher bandwidth than other media
– Data rate is also high
– The limitation of data rate and bandwidth
depends on the signal generation and reception
technology
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Fiber Optic Disadvantages
Cost
Installation/Maintenance
Fragility
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