Chapter Three

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Chapter Three

• The Media
• Conducted and Wireless

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Introduction
Chapter Three - The Media - Conducted and
Wireless

• The world of computer would not exist if there
  were no medium(??? ????) by which to transfer
  data
• The two major categories of media include
• Conducted media
• Wireless media

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Twisted Pair Wire (Conducted media)
Chapter Three - The Media - Conducted and
Wireless

• One or more pairs of single conductor(????) wires
  that have been twisted around each other
• Twisted pair wire is classified by category.
  Twisted pair is currently Category 1 through
  Category 7, although Categories 2 and 4 are
  nearly obsolete(????)
• two important laws from physics
• (1) A current passing through a wire creates a
  magnetic field around that wire
• (2) a magnetic field passing over a wire induces
  a current in that wire.
• Therefore, a current or signal in one wire can
  produce an unwanted current or signal, called
  crosstalk, in a second wire.

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Twisted Pair Wire
Chapter Three - The Media - Conducted and
Wireless

• Twisting the wires helps to eliminate
  electromagnetic interference between the two
  wires
• Shielding can further help to eliminate
  interference

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Chapter Three - The Media - Conducted and
Wireless

• If the two wires run parallel to each other the
  chance for crosstalk increases.
• If the two wires cross each other at
  perpendicular angles the chance for crosstalk
  decreases.

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Twisted Pair Wire
Chapter Three - The Media - Conducted and
Wireless
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Chapter Three - The Media - Conducted and
Wireless
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Coaxial Cable (Conducted media)
Chapter Three - The Media - Conducted and
Wireless

• A single wire wrapped in a foam insulation(?????
  ???? ) surrounded by a braided metal shield to
  block electromagnetic signals from entering the
  cable and produce noise, then covered in a
  plastic jacket. Cable comes in various
  thicknesses
• Baseband coaxial technology uses digital
  signaling in which the cable carries only one
  channel of digital data
• Broadband coaxial technology transmits analog
  signals and is capable of supporting multiple
  channels of data simultaneously

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Coaxial Cable
Chapter Three - The Media - Conducted and
Wireless
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Coaxial Cable
Chapter Three - The Media - Conducted and
Wireless
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Fiber Optic Cable (Conducted media)
Chapter Three - The Media - Conducted and
Wireless

• A thin glass cable approximately a little thicker
  than a human hair surrounded by a plastic coating
  and packaged into an insulated(????? ) cable
• A photo diode or laser generates pulses of light
  which travel down the fiber optic cable and are
  received by a photo receptor

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Chapter Three - The Media - Conducted and
Wireless

• How does a thin glass cable transmit data?
• A light source, called a photo diode, is placed
  at the transmitting end and quickly switched on
  and off to produce light pulses.
• These light pulses travel down the glass cable
  and are detected by an optic sensor called a
  photo receptor on the receiving end.
• The light source can be either a simple and
  inexpensive light-emitting diode (LED), laser.
• The laser is much more expensive than the LED,
  and it can produce much higher data transmission
  rates.
• Fiber optic cable advantages
• providing high-speed, low-error data transmission
  rates.
• Small noise as the light pulses bounce around
  inside the glass cable, this noise is
  significantly less than noise generated in
  twisted pair wires or coaxial cables
• More secure than twisted pair wires or coaxial
  cables, it is impossible to wiretap. Without
  physically break into the line

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Chapter Three - The Media - Conducted and
Wireless

• fiber-optic cable has two small disadvantages
• Light pulses can travel in one direction only.
  Thus, to support a two-way transmission of data,
  two fiber-optic cables are necessary.
• Its higher cost than twisted pair wires or
  coaxial cables

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Fiber Optic Cable
Chapter Three - The Media - Conducted and
Wireless

• Fiber optic cable is capable of supporting
  millions of bits per second for 1000s of meters
• Thick cable (62.5/125 microns) causes more
  ray(???? ) collisions, so you have to transmit
  slower. This is step index multimode fiber.
  Typically use LED for light source, shorter
  distance transmissions
• Thin cable (8.3/125 microns) very little
  reflection, fast transmission, typically uses a
  laser, longer transmission distances known as
  single mode fiber

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Fiber Optic Cable
Chapter Three - The Media - Conducted and
Wireless
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Fiber Optic Cable
Chapter Three - The Media - Conducted and
Wireless

• Fiber optic cable is susceptible(???? ) to
  reflection (where the light source bounces around
  inside the cable) and refraction(???????? )
  (where the light source passes out of the core
  and into the surrounding cladding(?????? ))
• Thus, fiber optic cable is not perfect either.
  Noise is still a potential problem

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Fiber Optic Cable
Chapter Three - The Media - Conducted and
Wireless
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Fiber Optic Cable
Chapter Three - The Media - Conducted and
Wireless

• It is very common to mix fiber with twisted pair
  in LANs

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Chapter Three - The Media - Conducted and
Wireless
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Wireless Media
Chapter Three - The Media - Conducted and
Wireless

• Radio, satellite transmissions, and infrared
  light are all different forms of electromagnetic
  waves that are used to transmit data
• Technically speaking in wireless transmissions,
  space is the medium
• Note in the following figure how each source
  occupies a different set of frequencies

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Chapter Three - The Media - Conducted and
Wireless
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Terrestrial(???? ) Microwave
Chapter Three - The Media - Conducted and
Wireless

• Transmission systems transmit tightly focused
  beams of radio signals from one ground-based
  microwave transmission antenna to another.
• Land-based, line-of-sight transmission
• Approximately 20-30 miles between towers
• Transmits data at hundred of millions of bits per
  second
• Signals will not pass through solid objects
• Popular with telephone companies and business to
  business transmissions
• might be less expensive in the long run than
  leasing a high-speed telephone line with monthly
  payment.
• once the system is purchased and installed, no
  telephone service fees are necessary.

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Terrestrial(???? ) Microwave

• Many microwave antennas are located on top of
  free-standing towers, The higher the tower, the
  farther the possible transmission distance.
• Another factor that limits transmission distance
  is the number of objects that might obstruct the
  path of transmission signals.
• Buildings, hills, forests, and even heavy rain
  and snowfall all interfere with the transmission
  of microwave signals.
• Disadvantages
• loss of signal strength and interference from
  other signals,
• in addition to the costs of either leasing the
  service or installing and maintaining the
  antennas.

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Chapter Three - The Media - Conducted and
Wireless
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Chapter Three - The Media - Conducted and
Wireless

• Often the microwave antennas are on towers or
  buildings

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Satellite Microwave
Chapter Three - The Media - Conducted and
Wireless

• Similar to terrestrial microwave except the
  signal travels from a ground station on earth to
  a satellite and back to another ground station
• Can also transmit signals from one satellite to
  another
• Satellites can be classified by how far out into
  orbit each one is (LEO, MEO, GEO, and HEO)

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Satellite Microwave
Chapter Three - The Media - Conducted and
Wireless
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Satellite Microwave
Chapter Three - The Media - Conducted and
Wireless

• LEO Low Earth Orbit 100 to 1000 miles out.
  Used for wireless e-mail, special mobile
  telephones, pagers, spying, videoconferencing
• MEO Middle Earth Orbit 1000 to 22,300 miles.
  Used for GPS (global positioning systems) and
  government
• GEO Geosynchronous(???????? ?? ?????) Earth
  Orbit 22,300 miles. Always over the same
  position on earth (and always over the equator(??
  ????????)). Used for weather, television,
  government operations
• HEO - highly elliptical orbit, which is used by
  governments for spying and by scientific agencies
  for observing celestial bodies(????????
  ???????).
• It follows an elliptical pattern. When the
  satellite is at its perigee (closest point to the
  Earth), it takes photographs of the Earth. When
  the satellite reaches its apogee (farthest point
  from the Earth), it transmits the data to the
  ground station. At its apogee, the satellite can
  also photograph objects in space.

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Satellite Microwave
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Satellite Microwave
Chapter Three - The Media - Conducted and
Wireless

• Satellite microwave can also be classified by its
  configuration
• Bulk carrier configuration
• the satellite system and all its assigned
  frequencies are devoted to one user.
• transmitting large amounts of data in a very
  short time, used for large application.
• entire satellite system by one user. For example,
  a telephone company use a bulk carrier satellite
  system to transmit thousands of long-distance
  telephone calls.
• Multiplexed configuration (Multiple users )
• The ground station accepts input from multiple
  sources.
• Single-user earth station configuration.
• each user employs his or her own ground station
  to transmit data to the satellite

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Chapter Three - The Media - Conducted and
Wireless
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Infrared Transmissions
Chapter Three - The Media - Conducted and
Wireless

• Transmissions that use a focused ray of light in
  the infrared frequency range
• Very common with remote control devices, but can
  also be used for device-to-device transfers, such
  as PDA to computer

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Bluetooth
Chapter Three - The Media - Conducted and
Wireless

• is a wireless technology that uses low power,
  short-range radio frequencies to communicate
  between two or more devices.
• Bluetooth is a specification for short-range,
  point-to-point or point-to-multipoint voice and
  data transfer
• Bluetooth can transmit through solid, non-metal
  objects Thus, a device that is transmitting
  Bluetooth signals can be carried in a pocket or
  briefcase.
• Its typical link range is from 10 cm to 10 m, but
  can be extended to 100 m by increasing the power

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Bluetooth
Chapter Three - The Media - Conducted and
Wireless

• Bluetooth will enable users to connect to a wide
  range of computing and telecommunication devices
  without the need of connecting cables
• Typical uses include phones, pagers, modems, LAN
  access devices, headsets, notebooks, desktop
  computers, and PDAs

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Bluetooth

• To appreciate the potential power of Bluetooth
  technology, consider examples
• You can automatically synchronize all e-mail
  messages between your PDA and your desktop/laptop
  computer
• as you approach your car, your PDA will tell the
  car to unlock its doors and change the radio to
  your favorite station
• as you walk up to the front door of your house,
  your PDA will instruct your house to unlock the
  front door, turn on the lights, and turn on an
  entertainment system,
• and as you sit in a business meeting, your
  PDA/laptop will wirelessly transmit your slide
  presentation to a projector and your notes to
  each participants PDA/laptop.

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Wireless LAN (IEEE 802.11)
Chapter Three - The Media - Conducted and
Wireless

• This technology transmits data between
  workstations and local area networks using
  high-speed radio frequencies
• access point is the connection into the wired
  portion of the local area network.
• Current technologies allow up to 54 Mbps
  (theoretical) data transfer at distances up to
  hundreds of feet)
• IEEE 802.11n. supporting a 100-Mbps signal
  between wireless devices and uses multiple
  antennas to support multiple independent data
  streams.
• All protocols802.11a, 802.11b, 802.11g, and
  802.11nare now called Wi-Fi.

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Free Space Optics
Chapter Three - The Media - Conducted and
Wireless

• Uses lasers, or, in some cases, infrared
  transmitting devices, to transmit data between
  two buildings over short distances, such as
  across the street.
• Data transfer speeds can be as high as 1.25 Gbps,
  higher in the future.
• Lasers lose their strength when transmitting
  through fog. Thus, if the fog is thick,
  transmission distances can be cut down to less
  than 50 meters
• Line of sight between buildings
• Typically short distances, such as across the
  street
• Newer auto-tracking systems keep lasers aligned
  when buildings shake from wind and traffic

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ZigBee

• relatively new wireless technology supported by
  the IEEE 802.15.4 standard. It has been designed
  for data transmission between smaller, often
  embedded, devices that require low data transfer
  rates (20250 Kbps) and low power consumption.
• For example, home and building automation
  (heating, cooling, security, lighting, and smoke
  detectors), industrial control, automatic meter
  reading, and medical sensing and monitoring.
• power consumption is so low that some suppliers
  claim that their ZigBee-equipped devices will
  last multiple years on the original battery.
• Bluetooth is best at replacing cables for short
  distances, while ZigBee will be good at sending
  low-speed signals over short to medium distances.

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Media Selection Criteria
Chapter Three - The Media - Conducted and
Wireless

• Cost
• Speed
• Distance and expandability
• Environment
• Security

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Media Selection Criteria - Cost
Chapter Three - The Media - Conducted and
Wireless

• Different types of cost
• Initial cost what does a particular type of
  medium cost to purchase? To install?
• Maintenance / support cost
• ROI (return on investment) price/performance
  ratio if one medium is cheaper to purchase and
  install but is not cost effective, where is the
  savings?

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Media Selection Criteria - Speed
Chapter Three - The Media - Conducted and
Wireless

• Two different forms of speed
• Propagation speed the time to send the first
  bit across the medium. This speed depends upon
  the medium. Airwaves and fiber are speed of
  light. Copper wire is two thirds the speed of
  light
• Data transfer speed the time to transmit the
  rest of the bits in the message. This speed is
  measured in bits per second