Telecommunications and Networks

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					CHAPTER 4

TELECOMMUNICATIONS
AND NETWORKS
Basic Definitions

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

               Marina G. Erechtchoukova    2
The Components of
Telecommunications Systems
   Hardware:
     Sending/receiving unit:
       Computers, Telephones, Fax, Radio sets,
        TV sets …
     Telecommunications devices
 Telecommunications media
 Telecommunications network


                 Marina G. Erechtchoukova         3
The Components of
Telecommunications Systems
(cont…)
   Communications software
     Communications protocols
   Communications applications:
     E-mail;
     Facsimile;
     EDI, EFT….
   Communications provider

                   Marina G. Erechtchoukova   4
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
      analog
                Marina G. Erechtchoukova   6
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



                  Marina G. Erechtchoukova     7
Analog vs. digital signals




           Marina G. Erechtchoukova   8
Signals
   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
                  Marina G. Erechtchoukova    9
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
      sources
   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.

                        Marina G. Erechtchoukova                 11
Telecommunications Devices
(cont…)
   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
    network
   Bridge connects networks with the same
    transmission protocol
   Router connects dissimilar networks
   Gateway – a network device which serves as an
    entrance to another network
                     Marina G. Erechtchoukova          12
Media for Data Transmission
   Conducted (cable) media
     Twisted-pair wire
     Coaxial cable
        baseband transmission – a single signal is
         used
        broadband transmission – available
         medium is divided into multiple channels.
     Fiber optic cable
   Wireless transmitting
                  Marina G. Erechtchoukova            13
    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


                     Marina G. Erechtchoukova          14
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

                    Marina G. Erechtchoukova         15
Networks
   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




                     Marina G. Erechtchoukova      16
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


              Marina G. Erechtchoukova   17
Network Communications Software
      Functions:
             Message formatting
             Error checking
             Communications log
             Data security
             Translation
      Main groups:
        Network Operating Systems
        Protocols
        Network Management Software

                    Marina G. Erechtchoukova   18
Protocols

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

                  Marina G. Erechtchoukova   19
OSI Model

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



              Marina G. Erechtchoukova   20
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
               message
Session        Dialog controller, synchronization

Presentation Translation, encrypting, compression
Application    Enables the user to access the
               network
                  Marina G. Erechtchoukova            21
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

                 Marina G. Erechtchoukova   22
Types of Data Processing in
Organizations
   Centralized processing: all processing
    occurs in a single location or facility
   Decentralized processing: processing
    devices are placed at various remote
    locations
   Distributed processing: computers are
    placed at remote locations but connected to
    each other via a network

                    Marina G. Erechtchoukova      23
Types of Distributed Data
Processing in the Organizations

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


                Marina G. Erechtchoukova   24

				
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posted:10/26/2012
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