4.1 Networks

• Network


  Two or more computers or other digital devices connected together in order to share data and resources
• Local area network (LAN)


  • Enables a group of computers that are in close proximity to each other to be networked
  • Typically used in a school, office or home
  • Allows resources such as files, printers, games and other software applications to be shared by the computers on the network
• Wireless local area network (WLAN)

  • Connects devices using radio waves, no cables required
  • Allows users to move around the area with their devices and remain connected
  • Allows one or more people to connect their mobile devices such as laptops, mobile phones, tablets, media players, speakers and printers
• Wide area network (WAN)


  • Connects separate LANs over a large geographical area
  • Connects cities, a country or many countries
  • Ensures that computers in one location can communicate with computers and users in other locations
• Internet


  • A global, public system of interconnected computer networks that serves billions of users worldwide and is therefore a wide area network
  • Provides many services including email and the world wide web (www)
  • The contents of the internet are not controlled
• Protocols


  Sets of rules governing how devices communicate with each other over networks
• Wi-Fi


  • A digital communications protocol that sets out how data is transmitted on wireless LAN
  • Each device must connect to a wireless access point to access the network
• Bluetooth


  • Wireless protocols allowing communication over short distances, usually up to 30 feet
  • Used to link personal devices to share data between them
  • Allows direct communication between devices
• Tethering is the linking of one device to another to connect to the internet
• Packet transmission


  1. Header (source/destination addresses, packet position)

  2. Body (payload, part of message/file)

  3. Footer (end of packet, error checking)
• Network interface card (NIC)


  • A component that connects a computer to a network
  • Formats data into required format according to network protocols
  • Has a unique MAC (media access control) address
• Hub


  • A device that connects computers in a network
  • Transmits all messages to all connected devices, not just the intended one
  • Creates a lot of unnecessary network traffic
• Switch


  • Transmits data only to the intended device based on MAC addresses
  • Builds a table of MAC addresses to improve network performance
  • Can send and receive information at the same time, faster than hubs
• Bridge


  • Connects different segments of a large LAN
  • Can prevent transmissions from one segment reaching others
  • Improves network security by isolating segments
• Router


  • Allows different networks to communicate
  • Used to direct data between networks in a WAN like the internet
  • Allows many computers to share an internet connection in a home network
• Routing tables list the routes to other networks on a WAN
• Star network


  Rules are needed so that all of the computers on the network work together. Otherwise, how would the receiving computer know when the message is complete or if there has been a transmission error?
• Packet


  Consists of three parts: Header (contains addresses of source and destination, and position of packet in message/file), Body (also known as payload, contains part of message/file), Footer (also known as trailer, informs receiving device it has reached end of packet and can be used for error checking)
• Router


  • Has a routing table that lists routes to other networks on the WAN. If it cannot directly connect to destination network, it has to send it via other networks along a route to the destination network
• Routing table


  A database that keeps track of paths, like a map, and uses these to determine which way to forward traffic
• Routing process


  1. Source computer splits file into packets and addresses them with recipient's IP address

  2. Packets are sent onto network using cables or radio waves

  3. Routers on network inspect each packet to find destination address and decide most efficient path for packet to take

  4. Routers can balance load across network on a millisecond-by-millisecond basis

  5. If there is a problem, packets can be routed around it

  6. Final router directs packet to correct recipient
• Packet switching


  More efficient than circuit switching as it does not require a dedicated line between communicating devices
• IP address


  A set of numbers used to identify one particular computer on the internet, like a postal address to allow data and messages to be sent directly to the correct computer
• The internet is a global network of interconnected computer networks
• TCP/IP


  The set of rules or protocols used by the internet, which all computers need a unique IP address for
• Intranet


  A private computer network within an organisation, such as a school or business, that uses internet technology but is separate from the global internet and cannot be accessed by outside users
• Extranet


  An intranet that allows users from other organisations to use it for specific purposes
• Types of networks


  • Internet
  • Intranet
  • Extranet
• Cloud computing


  The delivery of computer services over the internet, where services and data are housed in remote servers
• Advantages of cloud computing for business

  • Lower maintenance costs
  • Pay only for parts needed (software as a service)
  • Automatic software upgrades
  • Employees can work from anywhere
  • Data is automatically backed up
• Disadvantages of cloud computing for business

  • Requires internet access
  • Less control, reliant on provider
  • Providers' servers may be targeted by hackers
• Cloud storage


  The storage of digital data on remote servers
• Advantages of cloud storage

  • Data secure if local problem
  • Can access data anywhere
  • No need for expensive storage device
  • Multiple users can collaborate
• Disadvantages of cloud storage

  • Needs internet connection
  • Download/upload speeds affected
  • Hosting company could be hacked
  • Less control if data held by another company
  • May breach data protection laws
• These activities generate a huge amount of data every day, all of which is stored in the 'cloud' on remote servers in data centres around the world
• There are about 8.4 million global data centres, consuming about 3 percent of the total electricity generated worldwide, or 40 percent more than that generated by the whole of the UK
• It has been suggested that an uploading tax should be imposed
• Wireless Access Point (WAP)


  A device that acts as a bridge between wireless devices and a wired network, managing wireless traffic, providing security, extending network coverage, and supporting multiple devices