I'S' 3413 Introduction to Telecommunications in Business

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I.S. 3413Introduction to Telecommunications in
Business

• Chapter 4
• Physical Layer Concepts
• Dr. Jan Clark
• SPRING, 2003

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Physical Layer

• Lowest layer of OSI Model
• Communications media

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Common Elements of Physical Media

• Conduction medium for the physical signal
  (copper wire or glass or plastic fiber)
• Insulation protective barrier surrounding the
  conductor
• Sheathe or jacket outer covering

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Electrical Characteristics

• Capacitance ability to carry a signal without
  distortion (fig. 4.5)
• The lower the capacitance, the greater the
  distance a signal can cover without distortion
• Attenuation decrease in signal strength due to
  distance and high frequency (fig. 4.6)

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Clear vs. Distorted Signal
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Distorted,Weaker Signal
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Major Types of Communications Media

• Guided media - message flows through a physical
  media, such as TPW, coaxial cable, fiber optic
• Radiated media (unguided) - message is broadcast
  through space, such as infrared, microwave, or
  satellite

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Guided Media

• Twisted Pair Wire - insulated pairs of wire,
  twisted to minimize cross-talk and
  electromagnetic interference between wires
• Coaxial Cable - insulated copper core wire and
  outer shell for insulation. Greater transmission
  capacity than TPW, little distortion, less prone
  to interference, lower error rates
• baseband vs. broadband
• Fiber Optic Cable - high speed light pulses from
  lasers or LEDs. Greatest data carrying capacity,
  virtually error free (single mode preferred)

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UTP vs STP Cable
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Coaxial Cable
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Fiber Optic Cable
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Single Mode Fiber
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Electromagnetic Frequency Ranges
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Radiated Media

• Radio (wireless) data transmission - uses same
  basic principles as standard radio transmission
• Each device on the network has a radio
  receiver/transmitter set to specific frequency
• Infrared Transmission - uses low frequency light
  waves
• Line-of-sight (TV remotes)

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Radiated Media

• Microwave - extremely high frequency radio
  communication beam
• Line-of-sight
• Typically for long distance or voice
• Requires MW stations to boost signal and account
  for curvature
• Satellite - mostly geosynchronous
• Travel at speed of light
• Propagation delay

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Satellite Transmission
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Wireless LAN Technologies

• IEEE 802.11
• Primary Physical Layer Signaling Methods - DSSS,
  FHSS
• DSSS - Direct Sequence Spread Spectrum - spreads
  signal over wide band width. If receiver not
  tuned to signal frequency, appears as background
  noise
• FHSS - Frequency Hopping Spread Spectrum -
  transmits short bursts on different frequencies

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Wireless Access
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• What are the Advantages of Wireless Media?

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Disadvantages of Wireless Media

• Security of information
• Bandwidth issues
• Interference
• Distance