Telecommunications by jennyyingdi



     Chapter 5
       Chapter Objectives
• Understand the role of
  telecommunications in organizations
• Describe the evolution and types of
  computer networks
• Understand networking fundamentals
• Explain the role of the Open System
  Interconnect (OSI) model and network
  operating systems
The Role of Telecommunications
       in Organizations
 • Work Group Communication
   – E-mail
   – Video conferencing
 • Emerging Business Applications
   – Electronic Commerce
     • Uses the World Wide Web
   – Electronic Data Interchange (EDI)
     • Allows computer-to-computer links between
       trading partners
     Building Blocks of Data
• All communications require three things:
  – Senders and receivers that have
    something to share
     • Coded by sender
     • Decoded by receiver
  – A pathway or transmission media to send
    the message
  – Rules or protocols of communication
Human vs Computer
         Computer Networks
• Computers and other devices connected by
  a communications channel
  – Share files and other resources between users
• Channel: the transmission media
• Bandwidth: carrying capacity of the media
• Protocols: the physical and logical rules for
• Modem: sends signal over telephone line
  – Converts digital signal to analog and back again
     Evolution in Computer
• Centralized computing
  – Uses mainframes and “dumb” terminals
• Distributed computing
  – Uses separate computers
• Collaborative computing
  – Uses two or more networked computers
• Networks today include all three models
Centralized Computing Model
Distributed Computing Model
Collaborative Computing Model
  Classifications of Networks
• Private Branch Exchange (PBX)
  – A privately owned telephone switch
• Local Area Network (LAN)
  – Usually confined to a single building or site
• Wide Area Network (WAN)
  – Enterprise network - one organization
  – Global network
Private Branch Exchange
Local Area Network
Enterprise Network
     Networking Fundamentals
•   Servers, Clients, and Peers
•   Network Services
•   Transmission Media
•   Network Topologies
•   Network Access Control Methods
•   Major Standards
  Servers, Clients, and Peers
• Server-centric networks
  – Server
     • A network computer that makes services
       available to users
  – Client
     • Uses services provided by a server
• Peer-to-peer networks
  – Allow any computer or device to provide
    and request services
Servers, Clients, and Peers
          Network Services
• Offered by the network operating
  – File services
     • Store, retrieve, and move data
  – Print services
     • Control access to printers and fax machines
  – Message services
     • Deal with communication between network
  – Application services
     • Run software for network clients
       Transmission Media
• The physical pathway that carries
• Media characteristics
  – Bandwidth - transmission capacity stated in
    megabits per second (Mbps)
  – Attenuation - weakening of signal over
  – EMI - electromagnetic interference
• Two forms
  – Cable media
  – Wireless media
              Cable Media
• Twisted Pair
  – Two or more pairs of insulated copper wires
• Coaxial
  – Inner copper conductor surrounded by
    plastic insulation with outer braided foil shield
• Fiber Optic
  – Uses pulses of light to send data
  – Glass or plastic core surrounded by cladding
    with a tough outer sheath
          Wireless Media
• Infrared Line of Sight
  – Light waves transmit data on unobstructed
• High-Frequency Radio
  – Radio signals up to 39.6 meters
• Microwave Line of Sight
  – Terrestrial uses earth-based antennas
  – Satellite sends signals between antennas on
    earth and orbiting satellites
       Network Topologies
• Star Network
  – All nodes attached to center a hub
  – Messages must pass through the hub
• Ring Network
  – A closed loop
  – Messages move in one direction
• Bus Network
  – An open-ended line
  – Nodes receive message at the same time
Star Network
Ring Network
Bus Network
    Network Access Control
• Distributed Access Control
  – Token passing
    • Circulating electronic token prevents collisions
    • Must possess the token to transmit a message
• Random Access Control
    • “Listen” for quiet line; then send message
    • Collision occurs with simultaneous messages
    • Must wait and resend
Token Ring Operation
         Major Standards
• To ensure the interoperability and
  compatibility of networks
• Three major standards for LAN
  – Ethernet
  – Token-Ring
  – ARCnet
     Connectivity Hardware
• Computers can be physically connected
  in many ways
• Each device must be connected to the
       Key Components of a
          Local Network
•   Transmission Media Connectors
•   Network Interface Cards (NIC)
•   Modems (MOdulator/DEModulator)
•   Repeaters
•   Hubs
•   Bridges
•   Mutiplexers (MUX)
        Key Components for
•   Routers
•   Brouters
•   Channel Service Units (CSU)
•   Gateways
     Connectivity Software
• The OSI Model
• Network Operating Systems
         The OSI Model
• Protocol representing a group of
  specific tasks that allow data
  communication between two computers
• Each higher layer builds on the
  functions of the layers below
The OSI Model
The OSI Model and
 Message Passing
 Network Operating Systems
• Client/server architecture LANs
  – The system software runs on the file server
  – Part of the NOS runs on each workstation
• Peer-to-peer networks
  – NOS is installed on each attached
  – Runs on top of the local operating system

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