Chapter 7
Transmission Media
7.1
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Transmission Media
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7.2
The transmission media lies below the
Physcial Layer
It can be considered the Level-0 layer in
our Network Models.
Figure 7.1 Transmission medium and physical layer
7.3
Transmission Media
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Guided media
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Unguided media
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7.4
Twister pair copper wire
Coaxial cable
Fiber optic cable
Wireless
Figure 7.2 Classes of transmission media
7.5
Twisted Pair
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The twisted pair wire
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7.6
One wire carries signal
The other wire acts as a ground
Twisting cancels out unwanted signal (noise)
Figure 7.3 Twisted-pair cable
7.7
Figure 7.4 UTP and STP cables
7.8
Table 7.1 Categories of unshielded twisted-pair cables
7.9
Figure 7.5 UTP connector
7.10
Wire Guage
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40 Guages
Based on wire diameter
Bigger wire guage number implies smaller
diameter.
n = -39log92( d/.005 ) + 36
7.11
Wire Guage
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If the diameter of a wire is doubled,
The guage decreases by 6.
Thin wires have greater resistance
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7.12
Similar to a pipe carrying water.
Figure 7.6 UTP performance
7.13
Figure 7.7 Coaxial cable
7.14
Coaxial Cable
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7.15
The inner conductor carries the signal.
The shielding also acts as a ground.
Table 7.2 Categories of coaxial cables
7.16
Figure 7.8 BNC connectors
7.17
Figure 7.9 Coaxial cable performance
7.18
Fiber Optic Cable
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Capable of carrying greater bandwidth
compared to copper wire.
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7.19
Copper wire carries frequencies below 100KHz
Fiber optic carries frequencies beyond 10THz
More expensive than copper wire
Fiber Optic Cable
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7.20
Incident – incoming wave
Refraction – transmitted across the
boundary
Reflection – reflected within the boundary
Critical Angle
Total internal reflection
Index of refraction – a function of density
Fiber Optic Cable

Cladding – a transparent material less
dense than the inner core of an optical
cable.

7.21
Prevents refraction which leads to less loss of
signal
Figure 7.10 Bending of light ray
7.22
Snell’s Law
sin(a1)/sin(a2) = n2/n1
a1 = incident angle
a2 = refracted angle
n1 = index of incident material
n2 = index of refracted material
Index of refraction values
Air
Water
Cladding
Glass fiber core
n
n
n
n
=
=
=
=
1
1.333
1.52
1.62
Figure 7.11 Optical fiber
7.25
Figure 7.12 Propagation modes
7.26
Figure 7.13 Modes
7.27
Fiber Optic Cable

Multimode step-index fiber:

7.28
The sudden change in density between cable
and cladding will result in some distortion of
the signal.
Fiber Optic Cable
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Multimode graded-index fiber:
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7.29
A gradual change in density from the cable
center to the outer cladding and will result in
less distortion of the signal compared to stepindex fiber.
Graded-index fiber is more costly
Fiber Optic Cable
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Single-mode fiber:
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7.30
A narrow diameter of low index of refraction
step-indexed glass fiber.
A very focused beam of coherent light (similar
to a laser) passes near parallel to the fiber
edges.
Table 7.3 Fiber types
7.31
Figure 7.14 Fiber construction
7.32
Figure 7.15 Fiber-optic cable connectors
7.33
Figure 7.16 Optical fiber performance
7.34
Fiber Optic Cable
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7.35
High bandwidth measured in THz
Less attenuation
Immunity to interference
Light weight
Tapping is more difficult
Unidirectional
Expensive compared to copper wire.
7-2 UNGUIDED MEDIA: WIRELESS
Unguided media transport electromagnetic waves
without using a physical conductor. This type of
communication is often referred to as wireless
communication.
Topics discussed in this section:
Radio Waves
Microwaves
Infrared
7.36
Figure 7.17 Electromagnetic spectrum for wireless communication
7.37
Figure 7.18 Propagation methods
7.38
Satellite

7.39
Satellite is direct line of sight
communication (Covered in chapter 16)
Table 7.4 Bands
7.40
Figure 7.19 Wireless transmission waves
7.41
Multicast vs Broadcast
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7.42
Broadcast implies a single transmission to
all. (Analog radio or analog TV broadcast)
Multicast delivers data to a group of
destinations simultaneously; creating
copies when links to the destinations split.
(guided network transmissions)
Figure 7.17 Electromagnetic spectrum for wireless communication
7.43
Radio Wave Properties
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Frequency range from 3KHz-3GHz
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Radio waves can pass through walls
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7.44
FM, AM, TV, Cell Phone, etc.
Figure 7.20 Omnidirectional antenna
7.45
Figure 7.21 Unidirectional antennas
7.46
Figure 7.17 Electromagnetic spectrum for wireless communication
7.47
Note
Microwaves are used for unicast
communication such as cellular
telephones, satellite networks,
and wireless LANs.
7.48
Microwaves
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Range from 3GHz to 300GHz
High frequency microwaves do not pass
through walls
The bottom of the frequency range can
pass through walls
Capable of high bandwidth

7.49
Bluetooth is in the microwave range.
Figure 7.17 Electromagnetic spectrum for wireless communication
7.50
Note
Infrared signals can be used for shortrange communication in a closed area
using line-of-sight propagation.
7.51
Infrared Waves
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Range from 300GHz to 400THz
Do not pass through walls
Capable of high bandwidth
Lots of bands can be created reducing the
likelihood of interference from other
infrared devices.
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7.52
Remote control devices