Transmission

1
Chapter 7
Transmission Media
2
Figure 7-1
Electromagnetic Spectrum

• Voice band Twisted-pair or coaxial cables
• Visual light fiber-optic cable

3
Figure 7-2
Classes of Transmission Media
4
Figure 7-3
Categories of Guided Media

• Unshielded
• Shielded

5
Figure 7-4
Frequency Range for Twisted-Pair Cable
6
Figure 7-5
Twisted-Pair Cable

• A twisted pair consists of two conductors each
  surrounded by an insulating material.

7
Figure 7-6
Effect of Noise on Parallel Lines
8
Figure 7-7
Effect of Noise on Twisted-Pair Lines
9
Figure 7-8
Cable with Five Unshielded Twisted Pairs of Wires
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EIA Categories (UTP)

• Category 1 low-speed data communications
• Category 2 up to 4 Mbps
• Category 3 up to 10 Mbps (Now in general this
  category uses for most telephone system.
• Category 4 up to 16 Mbps
• Category 5 up to 100 Mbps

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Figure 7-9
UTP Connection

• The most frequently used of these plugs is an
  RJ45 connector with eight conductors, one for
  each wire of four twisted pairs.

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Figure 7-10
Shielded Twisted-Pair Cable

• Shield eliminates a phenomenon called crosstalk.
• .Shield must be connected to ground.
• STP uses the same conductors as UTP.
• STP more expensive than UTP.

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Figure 7-11
Frequency Range of Coaxial Cable
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Figure 7-12
Coaxial Cable

• Coaxial cable standards Radio Government (RG)
  ratings
• RG-8/9/11 Used in thick Ethernet.
• RG-58 Used in thin Ethernet.
• RG-59 Used for TV.
• Connector
• - T-Connector (thin Ethernet) terminators (bus
  topologies).

15
Figure 7-13
Refraction

• Light travels at 300,000 Km/sec in a vacuum.
• This speed decreases as the medium through which
  the light travels becomes denser.

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Figure 7-14
Critical Angle

• Critical angle The incident angle results in a
  refracted angle of 90 degrees.

17
Figure 7-15
Reflection

• Optical fibers use reflection to guide light
  through a channel.
• Information is encoded onto a beam of lights as
  a series of on-off flashes that represents 1 and
  0 bits.

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Figure 7-16
Propagation Modes

• Multimode Multiple beams move through the core
  in different paths.

19
Figure 7-17
Multimode Step-Index Fiber

• The density of the core remains constant from
  the center to the edges.

20
Figure 7-18
Multimode Graded-Index Fiber

• The density is highest at the center of the core
  and decreases gradually to its lowest at the edge.

21
Figure 7-19
Single-Mode Fiber

• Manufactured with a much smaller diameter than
  that of multimode fibers, and with substantially
  lower density.
• The decrease in density results in a critical
  angle that is close to enough to 90 degrees to
  make the propagation of beams almost horizontal.

22
Figure 7-20
Fiber Construction

• Cladding forming the fiber.
• Buffer protecting the fiber from moisture.

23
Optical Fiber

• Light sources for optical cable
• Light-emission diode (LED) Laser
• Connectors
• Advantages
• Noise resistance
• Less signal attenuation
• Higher bandwidth
• Disadvantages
• Cost
• Installation/maintenance
• Fragility

24
Figure 7-21
Radio Communication Band
25
Figure 7-22
Types of Propagation
26
Figure 7-23
Frequency Range for VLF

• Surface propagation
• VLF (very low frequency) waves are used mostly
  for long-range radio navigation and for submarine
  communication.
• - do not suffer much attenuation in
  transmission but are susceptible to the high
  levels of atomospheric noise active at low
  altitude.

27
Figure 7-24
Frequency Range for LF

• Surface propagation
• LF (low frequency) waves are used for long-range
  radio navigation and for radio beacons or
  navigational locators.
• Attenuation is greater during the daytime.

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Figure 7-25
Frequency Range for MF

• Tropospheric propagation
• MF (middle frequency) waves are used for AM
  radio, maritime radio, radio direction finding,
  and emergency frequencies.
• MF waves are absorbed by the ionosphere.
• Absorption increases during daytime.

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Figure 7-26
Frequency Range for HF

• Ionospheric propagation
• HF (high frequency) waves are used for ham radio,
  citizens band (CB) radio, international
  broadcasting, military communication,
  long-distance aircraft and ship communication,
  telephone, telegraph, and facsimile.
• HF waves move into the ionosphere, where the
  density difference reflects them back to earth.

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Figure 7-27
Frequency Range for VHF

• Line-of-sight propagation
• VHF (very high frequency) waves are used for VHF
  television, FM radio, and aircraft navigational
  aid.

31
Figure 7-28
Frequency Range for UHF

• Line-of-sight propagation
• UHF (ultrahigh frequency) waves are used for UHF
  television, mobile telephone, cellular radio,
  paging, and microwave links.

32
Figure 7-29
Frequency Range for SHF

• Line-of-sight propagation and space propagation
• SHF (super high frequency) waves are used for
  terrestrial and satellite microwave and radar
  communication.

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Figure 7-30
Frequency Range for EHF

• Space propagation
• EHF (extremely high frequency) waves are used for
  radar, satellite, and experimental communication.

34
Figure 7-31
Terrestrial Microwave

• Line-of-sight signal
• Repeater
• - To increase distance served by terrestrial
  microwave.
• Antennas
• - Parabolic dish
• - Horn

35
Figure 7-32
Parabolic Dish Antenna
36
Figure 7-33
Horn Antenna
37
Figure 7-34
Satellite Communication
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Figure 7-35
Satellite in Geosynchronous Orbit

• Uplink downlink
• Frequency band Table 7.2
• - C, Ku, Ka
• - Up/down link have different frequency.

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Figure 7-36
Cellular System
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Figure 7-37
Cellular Bands

• Each band 833 carriers
• - Carrier frequencies are spaced every 30Khz.
• - Two carriers are required for full-duple
  communications.

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Figure 7-38
Impairment Types
42
Figure 7-39
Attenuation

• Decibel (dB)
• - dB 10 x log10 (P2/P1)
• - P1 and P2 are the power of a signal at points
  1 and 2, respectively.

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Figure 7-40
Example 7.3
44
Figure 7-41
Distortion
45
Figure 7-42
Noise

• Types of noise
• - Thermal noise, induced noise, crosstalk, and
  impulse noise.
• - P1 and P2 are the power of a signal at points
  1 and 2, respectively.

46
Figure 7-43
Performance

• Throughput
• Propagation speed
• Propagation time

Throughput
47
Figure 7-44
Propagation Time
48
Figure 7-45
Wavelength

• ? c/f
• - ? wavelength
• - c propagation speed
• - f frequency

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Shannon Capacity

• Theoretical highest data rate for a channel
  (Shannon Capacity)
• C B log2 (1S/N)
• B Channel BW
• S/N Signal to noise ratio

50
Media Comparison

• Cost
• Speed
• Attenuation
• Electromagnetic interference (EMI)
• Security
• ??
• - Table 7.3 Transmission media performance

51
Summary

• Guided media
• Unguided media
• Transmission impairment