Telecommunications and Networks by pptfiles


									CHAPTER 4

Basic Definitions

 Telecommunications: the electronic
  transmission of signals for
 Telecommunications medium:
  anything that carries an electronic signal
  and interfaces between a sending
  device and a receiving device

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The Components of
Telecommunications Systems
   Hardware:
     Sending/receiving unit:
       Computers, Telephones, Fax, Radio sets,
        TV sets …
     Telecommunications devices
 Telecommunications media
 Telecommunications network

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The Components of
Telecommunications Systems
   Communications software
     Communications protocols
   Communications applications:
     E-mail;
     Facsimile;
     EDI, EFT….
   Communications provider

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The Components of
Telecommunications Systems
Telecommunications                 Telecommunications
      Device                             Device

  Sending                                   Receiving
    Unit       Communications                 Unit
              Channels and Media

Transmitter                                 Receiver

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Data and Signals
     Data
       Raw facts
       Static
     Signals
       Transmit data
       Dynamic
     Data and signals may be digital or
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Digital and Analog Data

   Analog data is represented as
    continuous waveform
     Example: audio tape
   Digital data is computer data –
    sequence of binary 0s and 1s:
     Example: data stored on the hard drive

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Analog vs. digital signals

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   Analog signals:
     Amplitude – height of wave above or below
      a reference point
     Frequency – a number of oscillations per
      time unit
     Phase determines the shift in time when
      wave obtains maximal value
   Digital signals:
     Baud rate
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Data Transmission
    Digital data using digital signals:
      Encoding
    Digital data using analog signals:
      Modulation
    Analog data using digital signals:
      Pulse code modulation
    Analog data using analog signals:
      AM, FM radio, broadcast television
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    Telecommunications Devices
   Modem
     an analog network is used to transmit digital data
   Fax modem
     Transmits images via standard telephone line
   Multiplexer
     an electronic device that allows a single communications
      channel to carry data transmitted simultaneously from many
   Private Branch Exchange
     a private telephone network used within an organization.
      Users of the PBX share a certain number of outside lines for
      making telephone calls external to the PBX.

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Telecommunications Devices
   Front-end processor – special purpose computer
    that managers communication
   Switch receives a message and forwards it to one of
    the output ports to reach another device on the same
   Bridge connects networks with the same
    transmission protocol
   Router connects dissimilar networks
   Gateway – a network device which serves as an
    entrance to another network
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Media for Data Transmission
   Conducted (cable) media
     Twisted-pair wire
     Coaxial cable
        baseband transmission – a single signal is
        broadband transmission – available
         medium is divided into multiple channels.
     Fiber optic cable
   Wireless transmitting
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    Wireless Media (continued …)
   Terrestrial microwave
   Satellite - digital transmission
     Geostationary earth orbit (GEO) - 22,300 miles
     Medium earth orbit (MEO) - 6,000 miles
     Low earth obit (LEO) - 400 to 1,000 miles
   Radio
     High bandwidth

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Wireless Media (continued …)
   Cellular radio technology
     transfers calls from one cell to another
   Mobile computing
     occurs on radio-based networks that transmit
      data to and from mobile computers
   Personal communications services
     use lower-power and higher-frequency means
   Infrared
     commonly used in remote control units

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   Personal Area Networks interconnect IT devices
    within 33 feet
   Local Area Networks connect two or more
  communications devices within 2,000 feet
 Metropolitan Area Networks networks that serve
  an area of 3 to 30 miles
   Wide Area Networks large networks that serve
    large geographical regions

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Computer Networks

 Computer network: computers and the
  communications media, devices, and
  software needed to connect two or more
  computer systems or devices
 Network nodes: the computers and/or
  devices on the networks

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Network Communications Software
      Functions:
             Message formatting
             Error checking
             Communications log
             Data security
             Translation
      Main groups:
        Network Operating Systems
        Protocols
        Network Management Software

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 NOS refers to a protocol to implement
  data transmission
 Protocol – set of rules for data
 Main conceptual components:
     Syntax
     Semantics
     Timing

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OSI Model

 Open Systems Interconnection –
  network architecture model
 Consists of layers
 Each layer describes the services

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Seven Layers of the OSI Model
Physical       Coordinates hardware devices to
               perform a bit stream transmission
Data Link      Framing, flow, error, and access
               control, physical addressing
Network        Logical addressing, routing the data to
               final destination
Transport      Source-to-destination delivery of entire
Session        Dialog controller, synchronization

Presentation Translation, encrypting, compression
Application    Enables the user to access the
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A mnemonic for remembering
the layers of the OSI Model
   Physical          Please

   Data Link         Do

   Network           Not

   Transport         Touch

   Session           Steve’s

   Presentation Pet
   Application       Alligator

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Types of Data Processing in
   Centralized processing: all processing
    occurs in a single location or facility
   Decentralized processing: processing
    devices are placed at various remote
   Distributed processing: computers are
    placed at remote locations but connected to
    each other via a network

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Types of Distributed Data
Processing in the Organizations

   Terminal-to-Host Processing
   Peer-to-peer processing
   File Server Processing
   Client/Server Architecture and

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