Networks

• Data communication


  The transmission of data and information between two or more computers
• Examples of data communication

  • Electronic mail (email)
  • Voicemail
  • Facsimile (fax)
  • Telecommuting
  • Video conferencing
  • Electronic data interchange (EDI)
  • Global positioning systems (GPS)
  • Online services
  • Social media
  • Internet
• Network: two or more devices that are connected and are caoabe of sharing data and infromation
• Uploading data


  Sending data from your computer to another computer on the network or the Internet
• Downloading data


  Receiving data to your computer from another computer on the network or the Internet
• Point-to-point network


  • Direct link between two computers
• Broadcast network


  • One computer transmitting data and information to serve the needs of several terminals or computers
• Microwave signals


  High-frequency radio signals that travel through the atmosphere, used for high-volume, long-distance communication
• Microwave signals travel in straight lines and can be bounced off satellites to cover longer distances
• Low-orbit satellites


  Travel closer to earth, so weaker signals can be processed while consuming less power
• System using microwaves


  • Cellular network supporting two-way communication
• Local Area Network (LAN)


  • A few computers, printers and large hard disks linked together, usually on one site
• Wide Area Network (WAN)


  • Many small and large computers, located on different sites spread over a large geographical area or in different countries, linked together
• Metropolitan Area Network (MAN)


  • Large enough to extend to an area like a city or campus, owned and operated by a single organisation
• Stand-alone computer


  Computer not networked
• Wireless Local Area Network (WLAN)


  • A LAN that allows laptops or remote computers to connect wirelessly
• Components needed to connect computers to a LAN using cables

  • Network cabling
  • Network card in each computer
  • Hub(s)
  • File server
  • System software
• Hub


  Central device that computers are connected to in a network
• File server


  High-performance computer containing large capacity hard disk drives available to all network users
• Hierarchical network


  • One powerful computer controlling others
• Peer-to-peer network

  • No file server, each computer acts as a server to the others
• Network layouts (topologies)


  • Star
  • Bus
  • Ring
• Star network


  • All nodes connected to a central hub
• Bus network


  • Network nodes in a line, if cable breaks network is split
• Ring network


  • Last node connected to first, forming a loop, if cable breaks affects all computers
• Wireless networks


  Linked by infrared waves, microwaves or radio waves
• Transceiver


  Device to send and receive data in a wireless network
• Bluetooth


  Wireless connectivity to replace cables
• Wi-Fi


  Wireless high-speed access to a network or the Internet
• Hotspot


  Public area offering Internet access over a WLAN
• Advantages of networked computers compared to stand-alone

  • Access data/resources from any workstation
  • Share files, messages, resources, programs
  • Possible to work on same file collaboratively
  • Activities/storage controlled by network manager
• Disadvantages of networked computers compared to stand-alone

  • Network hardware can be costly
  • Network crash can stop everyone using computers
  • Security risks from more users and viruses
  • Need for network manager
• Communication channel


  Method or medium used for transmitting data
• Characteristics of communication channels

  • Transmission mode
  • Direction of data flow
  • Transmission medium
  • Transmission speed
• Transmission mode


  Number of characters that can be transmitted in one second
• Data can be transferred only by disk or by modem. Will need to use an external hard drive or online storage, which can be time consuming and unreliable
• Network cards, cabling, hubs and servers can be costly. Wireless connection to a network may result in reduced data transfer rates and unreliable connectivity
• If the file server stops working (known as a 'crash'), it can stop everybody on the network from using a computer
• Poor security. With more users there is a greater risk of computer viruses and of unauthorised users (hackers) gaining access to network data
• Need for network manager to manage the system. This can be costly