Communications _ Networks by zhouwenjuan

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									Communications & Networks

   Standard Grade Revision:
          Networks
         What is a Network?
• A series of computers linked together so
  can send and receive data.
• We use them for sending e-mails,
  downloading files, shopping, etc
                    • They are divided into
                      two types:
                       – Local Area Network
                         (LAN)
                       – Wide Area Network
                         (WAN)
     Local Area Network (LAN)
• Cover a small area such as one room or
  building.
  – The school has a LAN
• Each computer on a LAN is called a station
• One station is called
  the file server.
  – The file server is where
    all the data & files are
    kept
           Advantages of a LAN
•   Share data
•   Share peripherals (resource sharing)
•   E-mail
•   Passwords keep data secure
•   Different levels of access
    – stop unauthorised access
• Flexible access
    – Use any station connected to the LAN
• Many users can use same document at the
  same time (workgroup computing)
     Transmission media for LAN
• Stations can be connected by cables or
  wireless technology
• Cables:
   –Unshielded Twisted Pair of copper
    wire (UTP)
     • Uses electrical signals to transmit data
     • Cheaper but can get interference
   –Optical fibre
     • Uses light beams to transmit data
     • Expensive but doesn't get interference
    Transmission media for LAN
• Wireless
  – Infrared communication
     • Like the TV controls
  – Bluetooth
     • Range of about 10 metres
  – WIFI (Wireless Fidelity Alliance)
     • Range of about 12-50
       metres


          Bluetooth & WIFI use radio waves
    Wide Area Networks (WAN)
• Connect computers across large distances
• Spread across countries & cities worldwide
  using telecommunications links
• Similar advantages to LAN but on a bigger
  scale.
 Transmission Media for WANs
• Telecommunications links
  – The communication of information over a
    distance using:
     • Microwave transmission
     • Satellite links
     • Optical Fibre
          Network Security
• Security methods include:
  – Passwords & user IDs
  – Encryption
  – Physical methods
        Lesson Objectives
• We will learn about:
  – Client Server Networks

  – Network Interface Cards

  – Multi-Access Computers

  – Social, Legal & Ethical Issues
               Recap - LAN

• Area:                    • Advantages of LANs
                             – Share data
• Stations & File Server     – Resource sharing
                             – Different levels of
• Transmission Medium:         access
                             – Flexible access
                             – workgroup computing
               Recap - WAN

• Area:                  • Network Security:


• Transmission Medium:
  – Telecommunications
    Links
     Client & Server Networks
• A method of network organisation
• Each workstation is called a client
• Each workstation is connected to a central
  system called a server
• The server can be used for:
  – Holding all the data files and application
    software
  – Organising printing on the network
  – Organising the clients’ access to the internet
 Client / Server Network



Client    Client
                    Client



Printer
                    Client
          Server
       Network Interface Card
• Allows the computer system to communicate
  with the network
• Every device that is connected to the LAN will
  need a NIC, for example, computer, printer and
  scanner.
                • It take the data sent by your
                   computer
                    – stores it in its own memory
                      locations,
                    – then adapts it ensuring it
                      follows the communication
                      rules
       Multi-Access Computers
• Enable many users to:
  – Access the system at the same time
  – Share the proccessing power of the system
  – Shave the available memory
  – Share the data on backing storage
• The terminals attached to these computers
  useually have no processing power of their
  own.
• The terminals would be made up of just a
  monitor and keyboard
             Social Issues
• Teleworking
  – Process of using a WAN to work from home
• WANs can improve communications for
  people in remote areas
• Some people can’t afford the cost so a
  gap could form between the “Information
  Rich” and the “Information Poor”
• Some people believe that computers
  cause social isolation
           Legal & Ethical Issues
• Legal:
  – Computer Misuse Act
  – Copyright, Designs & Patents Act
  – Data Protection Act

• Ethical:
  – Invasion of personal privacy
  – Censorship & freedom of speech
Communications & Networks



   Electronic Communications
  Lesson Objectives

• Electronic Communication
• Text/Instant Messaging
• E-Mail
  • Advantages & Disadvantages
  • File Attachments
• Netiquette
Electronic Communication
        • The process of sending
          and receiving electronic
          messages.
        • Electronic messages
          include:
          – Electronic mail
          – Text messaging
          – File transfer (attachments)
           Text Messaging
• Types:
  – Short text message.
  – Instant messaging.

• Language used:
  – Casual/Informal
  – Abbreviations
  – Acronyms
                         E-mail
• Advantages:                       • File Transfer
  –   Fast compared to post           – Files can be attached
  –   Cheap – ISP connection only     – Size limit
  –   Web mail – access anywhere      – Attached viruses
  –   Send multiple copies (CC)
  –   Organise folders

• Disadvantages:
  – Spam
  – Viruses
  – Lack of Netiquette
                Netiquette
• Code of conduct used in e-communications

        •   DON’T WRITE IN CAPS!
        •   Don’t leave the Subject Field blank
        •   Don’t over use Formatting
        •   Don’t give out personal details
        •   Don’t start Flame Wars (Trolling)
        •   Use proper English in e-mails.
        •   Don’t send dumb jokes, chain mail, etc
Communications & Networks


       The Internet
             • Internet Services
             • Accessing the
               Internet
 Lesson      • The World Wide
Objectives     Web
             • Search Engines
             The Internet




• Enables computers and networks
  worldwide to connect with each other
• The network of networks
            Internet Services

• World Wide Web (www or just web)
  – Used for browsing or searching
• E-mail
  – Communication & exchange of information
• File transfer
  – Sending & receiving large
    amounts of information
Accessing the Internet
 • Internet ready computer
 • Internet Service Provider (ISP)
   – A company that provides access to the
     internet
 • Browser
   – Software used to view web pages
 • Email client
   – Program for sending and receiving email
       Accessing the Internet
• Modem
  – The telephone line doesn’t understand binary
  – A modem is needed to translate for the computer

              • Dial-Up
                 – Uses a modem and an ordinary
                   phone line to dial up the number of
                   your ISP that connects you to the
                   internet.
              • Broadband
                 – Uses either a digital subscriber line
                   (DSL) or a cable modem
           World Wide Web
• Information is stored in web pages on web
  sites
• These pages can be viewed in a browser
• They are found by an address such as:
  – www.google.co.uk
  – www.msn.com
• Hyperlinks are used to ‘travel’ around the
  web
              The Web - HTML
• Hyper Text Mark-up Language
• The language used to write web pages
<"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
  <meta name="Description" content="Your description">
  <meta name="Keywords" content="first, second, third">
  <title>Title of the document</title>
  <base href="http://www.yourdomainname.com/images/">
</head>
  <body>
  The body of the document
</body>
</html>
            Search Engine
• Special web site to help you find
  information
• A big database!
• Some of the main search engines:
             • Software on the
               internet
             • Video conferencing
 Lesson      • Streaming media
Objectives   • Internet services
             • Mobile Internet
      Software on the Internet
• Freeware
  – Free software but the author still holds the
    copyright
  – You are not allowed to change it
• Shareware
  – 30-Day trial period
  – After that either pay for it or delete it
     Software on the Internet
• Commercial
  – Pay full price up front
  – Limited to one backup copy
  – Licence agreements are very detailed
        Video Conferencing
• Using networks to send audio and visual
  data.
• Enables people to have face-to-face
  meetings
• Saves time and money
• No need to travel long distances for
  business
      Video\Audio Streaming
• The internet is used to send data one way
• Online radio stations do this
• Uses large amount of network bandwidth
      Other Internet Services
• Chat & instant messaging
  – Text based communication
  – Communication is in real time (instant)
• Weblogging (Blog)
  – A type of online diary
  – Used for both business & personal
• Bulletin boards
  – Electronic notice board
            Mobile Internet
• Using the internet while on the move
  – Walk ‘N’ Surf
• Devices include
  – Mobile phones, Laptops, palmtops

								
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