Ch7_1_TransmissionMedia

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Transcript Ch7_1_TransmissionMedia

Transmission Media
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Transmission Media
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Background
Guided Media
Unguided Media
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Transmission Media
Electromagnetic Spectrum
Visible light, 430-750
THz
Power,
voice
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Radio communication Radio, Infrared
microwave, satellite
light
3KHz
Ultraviolet
light
X. Gamma,
cosmic rays
300 GHz
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Transmission Media :
Background
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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
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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
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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
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CAT2
– Suitable for voice and data communication
– Speed is up to 4 Mbps
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CAT3
– Required to have at least 3 twist per foot
– Some other requirements
– Transmission rate  up to 10 Mbps
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CAT4
– Similar requirement as CAT3
– Transmission rate  up to 16 Mbps
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CAT5
– Transmission rate  up to 100 Mbps
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UTP Connector
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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
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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
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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
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Current technology supports two form for
propagating light along optical channel
– Multimode
– Single mode
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Multimode
– Multiple beams move through the core in
different paths
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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
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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
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Noise resistance
– Noise is not a factor to light
– External light is blocked from the channel by the
outer jacket
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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
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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
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Cost
Installation/Maintenance
Fragility
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