Networks & topologies

• Network


  A group of interconnected computers/devices connected for the purpose of communication
• Network


  • Connected by wired medium like cables or wireless medium like Wi-Fi
  • A computer/device not connected to a network is called a stand-alone device
• Many different types of computer are connected to some form of network today, including PCs, smartphones, smartwatches, etc.
• Advantages of using networks


  • File sharing
  • Hardware sharing
  • Communication via email, chat, video
  • Roaming access
• Additional benefits of larger networks used by businesses and schools

  • Centralised maintenance and updates
  • Centralised security with anti-virus and firewalls
  • User monitoring
  • Levels of access
• Disadvantages of networks


  • Cost of additional equipment
  • Management by technical staff
  • Spread of malware
  • Hacking risks
• Once a device is connected to a network, it is possible that data may be accessed without the device owner's permission
• Local area network (LAN)


  A network of computers that covers a small area, eg a school or college
• Wide area network (WAN)


  A network that spans across a building, buildings or even countries, eg the internet
• A LAN is geographically confined to one building or site
• A WAN is spread over a wide geographical area
• Examples of LANs


  • Networks employed by small businesses, small organisations, schools, colleges, universities and in homes
• LANs are owned and maintained by the organisation
• Organisations that have more than one office or branch, such as banks, tend to use a WAN
• The WAN allows the head office to communicate and share data with the sub-offices and branches
• Communication in a WAN is done through national telephone infrastructures or via wireless transmission
• Each office or branch in a WAN has its own LAN that is connected together using the WAN
• The internet is essentially a huge, international WAN
• Network


  A group of interconnected computers/devices
• Network performance


  Response time - how fast a message can be sent or how quickly a document can be retrieved
• Factors that affect network performance


  • Number of devices on the network
  • Bandwidth of the transmission medium
  • Type of network
  • Network traffic
  • Network latency
  • Number of transmissions
  • Transmission errors
• Bandwidth


  Measures the amount of data that can transfer through a communications channel over a given period of time
• Typical bandwidth of transmission media

  • Twisted copper wire: Up to 10 gigabits (Gb) per second
  • Fibre-optic cable: Up to 100 gigabits (Gb) per second
  • Wi-Fi (home networks): Up to 600 megabits (Mb) per second
  • Business Wi-Fi: Up to 6 gigabits per second
• Bandwidth sharing


  Bandwidth of the medium is shared between each connected device
• If ten devices were connected, the bandwidth allocated to each device would drop to 5.4 Mb per second, thereby reducing the rate at which data can be sent to any particular device
• Latency


  A measure of how long it takes a message to travel from one device to another across a network
• Latency

  • Low latency experiences few delays in transmission
  • High latency experiences many delays
• Hub-based network


  Usually experiences higher latency than a switch-based network because hubs broadcast all messages to all devices
• The greater the number of devices connected to a network, the more important the choice of transmission medium becomes
• Many networks include a combination of fibre-optic cables, twisted copper wire, and Wi-Fi
• Collision


  The result of two devices on a network trying to communicate with each other simultaneously
• The greater the number of devices on a network, the more chance of a collision occurring, and the longer it takes to transmit a message
• Local area network (LAN)


  A group of interconnected computers/devices
• Hardware


  The physical parts of a computer system, eg a graphics card, hard disk drive or CD drive
• Network interface controller (NIC)


  A circuit board that is installed in a computer so it can be connected to a network
• Wireless


  A connection that does not need wires and transmits data through radio signals
• Transmission medium


  Physical devices that are used to transfer data
• Router


  A device for connecting computers and other network capable devices together to form a network
• Hub


  A piece of hardware used in computer networks used to connect multiple devices
• Switch


  A device for connecting computers and other network capable devices together to form a network