Telecommunications - PowerPoint PPT Presentation

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Telecommunications

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Telecommunications Communications Model Trasmission Modes Transmission Direction Transmission Media Communication Networks Communications Model Transmission of ... – PowerPoint PPT presentation

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Title: Telecommunications


1
Telecommunications
  • Communications Model
  • Trasmission Modes
  • Transmission Direction
  • Transmission Media
  • Communication Networks

2
Communications Model
Message
Medium
Sender
Receiver
3
Transmission of Digital Data over Analog Links
4
Transmission Modes
start bit
start bit
end bit
end bit
start bit
end bit
byte
byte
byte
Asynchronous transmission Low-speed transmission
of one character at a time, using control bits
(i.e., start stop bits)
byte
byte
byte
byte
Synchronous transmission High-speed simultaneous
transmission of large blocks of data
5
Transmission Direction
  • Simplex transmission
  • Transmission occurs in one direction only
  • e.g., radio or TV waves
  • Half-duplex transmission
  • Transmission occurs in both directions, but only
    one at a time
  • e.g., Walkie-Talkie, CB radio, pagers
  • Full-duplex transmission
  • Transmission occurs in both directions
    simultaneously
  • e.g., telephones

6
Transmission Medium wire-based
  • Twisted wire pair
  • A pair of copper wires are twisted to avoid
    signal interference
  • The cost is low, and widely used in local loops
    of telephone net.
  • Subject to communication noises
  • Coaxial cable
  • Layers of copper conductors covered with
    shieldings
  • can transmit data, video, voice signals over one
    line
  • Fiber optics cable
  • Fastest wire-based transmission medium
  • The cost is too high, and ideal as a corporate
    back-bone cable to interconnect many LANs

7
Transmission Medium wireless
  • Terrestrial microwave
  • microwave dishes needed at certain intervals
    (appr. 50km)
  • allows for very high-speed transmissions, and
    used by phone companies or common carriers
  • Satellite microwave
  • involves uplinks downlinks travelling to and
    from the satellite
  • widely used for GPS applications
  • Cellular communication
  • An area is divided up into many small cells, and
    an antenna installed in each cell handles signal
    transmissions

8
Microwave and Satellite Transmissions - Contd
The satellite and the antenna
Microwave antenna
9
Mobile telecommunications
IMT-2000 video phone
Cellular phone
10
Communications Networks
  • LAN(Local Area Network)
  • ideal for small area networking needs (e.g.,
    room, floor, building)
  • widely used to support computing needs in the
    office environment
  • MAN(Metropolitan Area Network)
  • a backbone cable linking small LANs throughout
    an organization
  • e.g., A network interconnecting agencies of an
    insurance firm
  • WAN(Wide Area Network)
  • networking support covers a large geographical
    area
  • used by airlines, banks, etc.
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