Communications Systems

1
CommunicationsSystems
Section B
Communications Channels
CHAPTER 11

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Section B
Communications Channels
Chapter 11
Section PREVIEW
Section D
Section B
You will be able to

• Discuss the advantages and disadvantages of
  Internet access over telephone, cellular phone,
  cable TV, and satellite systems

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Twisted-Pair Cable Whats the most typical type
of communications channel?
Chapter 11
Section B
Section B

• Telephone systems and LANs use miles and miles of
  twisted-pair cables.

Twisted-pair cable terminates with a plastic
RJ-45 connector.
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Twisted-Pair Cable Whats the most typical type
of communications channel?
Chapter 11
Section B
Section B

• Voice-grade cable (Category 1 cable)
• recommended for transmitting voice but not data
• Data-grade cable
• suitable for data transmissions
• Select a Category 5 unshielded or shielded cable
  with RJ-45 connectors to connect your network
  interface card to a network hub.

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Coaxial Cable What about other popular cable
options?
Chapter 11
Section B
Section B

• Coaxial cable - high-capacity communications
  cable consisting of a copper wire conductor
• carries television signals

Coaxial cable contains shielding which
increases bandwidth.
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Coaxial Cable What about other popular cable
options?
Chapter 11
Section B
Section B

• Coaxial cable
• has excellent bandwidth
• more expensive
• more difficult to work with than twisted-pair
• Fiber-optic cable is replacing coaxial and
  twisted-pair cable where high bandwidth is
  required.

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Fiber-Optic Cable Whats so special about
fiber-optic cable?
Chapter 11
Section B
Section B

• Fiber-optic cable is a bundle of extremely small
  tubes of glass called optical fibers.
• thinner than human hair

Fiber-optic cable
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Fiber-Optic Cable Whats so special about
fiber-optic cable?
Chapter 11
Section B
Section B

• Fiber-optic cable
• new development
• does not conduct or transmit electrical signals
• miniature lasers send pulses of light
• each fiber is a one-way communications channel
• light signals encounter little resistance

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Fiber-Optic Cable Whats so special about
fiber-optic cable?
Chapter 11
Section B
Section B
Fiber-optic cable
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Fiber-Optic Cable Whats so special about
fiber-optic cable?
Chapter 11
Section B
Section B

• Single-mode cable
• very narrow core
• transmission speeds exceed 50 gigabytes per
  second
• Multi-mode cable
• wide, 50-100 micron core
• easier to install
• choice for computer networks

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Radio and Infrared Links Dont some data
communications use wireless links?
Chapter 11
Section B
Section B

• It is possible to communicate without using
  wires.
• Radio waves - provide wireless communications
• cellular phones
• require FCC license
• Radio communications link uses a transmitter to
  send the signal and a receiver to pick up the
  signal.
• slower than cables
• susceptible to interference

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Radio and Infrared Links Dont some data
communications use wireless links?
Chapter 11
Section B
Section B

• Infrared transmissions use a frequency rate below
  the visible light of spectrum.
• does not require FCC license
• an example of line-of-sight communication
• transmitter that sends signal must have an
  unobstructed path to receiver

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Radio and Infrared Links Dont some data
communications use wireless links?
Chapter 11
Section B
Section B
Printing using an infrared sensor
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Microwave and Satellite Links How do
communications satellites fit into the picture?
Chapter 11
Section B
Section B

• Microwave - an electromagnetic wave with a
  frequency of at least 1 gigahertz (GHz)
• Microwave transmission sends a high-frequency
  signal from a transmitting station to a receiving
  station.
• stations must be within 30 miles
• Many communications systems transmit microwave
  signals between a land-based ground station and a
  satellite.

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Microwave and Satellite Links How do
communications satellites fit into the picture?
Chapter 11
Section B
Section B

• A telecommunications satellite contains a
  transponder (receives signal, amplifies signal,
  and retransmits signal).

Low-earth orbit communications system
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Microwave and Satellite Links How do
communications satellites fit into the picture?
Chapter 11
Section B
Section B

• Transmissions from a satellite transponder are
  sent to satellite dishes.
• Satellite dishes
• catch transmissions on parabolic surface
• reflects these signals to a feedhorn
• Feedhorn - small metal probe that is a microwave
  antenna

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Section B
Communications Channels
Chapter 11
Section A
QuickCheck
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B
Q U I C K C H E C K
Chapter 11

• 1. UTP has the highest bandwidth of any cable you
  can buy. True or false?

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B
Q U I C K C H E C K
Chapter 11

• 1. UTP has the highest bandwidth of any cable you
  can buy. False.

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B
Q U I C K C H E C K
Chapter 11

• 2. _____________ cable is typically used for
  local area networks and cable television.

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B
Q U I C K C H E C K
Chapter 11

• 2. Coaxial cable is typically used for local area
  networks and cable television.

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B
Q U I C K C H E C K
Chapter 11

• 3. Twisted-pair and coaxial cables transmit
  ____________ signals, whereas fiber-optic cables
  transmit pulses of __________.

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B
Q U I C K C H E C K
Chapter 11

• 3. Twisted-pair and coaxial cables transmit
  electrical signals, whereas fiber-optic cables
  transmit pulses of light.

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B
Q U I C K C H E C K
Chapter 11

• 4. The highest-capacity fiber-optic cable is
  called ____________ cable.

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B
Q U I C K C H E C K
Chapter 11

• 4. The highest-capacity fiber-optic cable is
  called single-mode cable.

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B
Q U I C K C H E C K
Chapter 11

• 5. Wireless communications channels are generally
  slower than cables. True or false?

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B
Q U I C K C H E C K
Chapter 11

• 5. Wireless communications channels are generally
  slower than cables. True.

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B
Q U I C K C H E C K
Chapter 11

• 6. Satellites send a high-frequency ____________
  signal to a ground station or satellite dish.

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B
Q U I C K C H E C K
Chapter 11

• 6. Satellites send a high-frequency microwave
  signal to a ground station or satellite dish.

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Section B
Communications Channels
Chapter 11
Section A
End of Section
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