1.3

• Network


  A group of devices connected together so they can communicate with each other and share resources
• Network size and complexity


  • Small (e.g. mobile phone hotspot)
  • Large (e.g. the internet)
• advantages and disadvantages of using networks

  • Allow communication (e.g. text, email, instant messaging, internet telephony)
  • Allow sharing of resources (e.g. printers, files)
  • Introduce security risks (e.g. malicious files, rogue websites)
• Shared network devices


  • Allow sharing of expensive hardware (e.g. printers, storage)
  • Require careful access management
• Shared files


  • Require appropriate access permissions to be set
• Multi-user systems


  • Allow multiple users to access the same system (e.g. pupil attendance)
  • Often database systems with sophisticated access restrictions
• Central backup procedures


  • Allow data to be backed up centrally
  • Allow important systems to be mirrored for failover
• Centralised software deployment


  • Allows software and updates to be rolled out centrally
  • Allows software to be used "in the cloud"
• Network interface card


  Hardware required to access a network
• Network account


  Provides access to network resources (e.g. shared devices, storage)
• Network management considerations


  • Wired or wireless
  • Network topology
  • Peer-to-peer or client-server
  • Security systems
• Advantages of networks


  • Share expensive hardware
  • Share files
  • Multi-user systems
  • Track user activity
  • Central backups
  • Central software deployment
• Disadvantages of networks


  • Extra hardware costs
  • Require network management
  • Greater security risks
• Personal area network (PAN)


  Network of connected devices within a few metres of each other
• Local area network (LAN)

  Network located in a small geographical area (e.g. home, office, school)
• Wide area network (WAN)


  Network that connects two or more LANs over a wider geographical area
• Client-server network


  Clients request resources from servers
• Peer-to-peer network


  No central servers, devices share resources directly
• Network topology


  The arrangement and connections of devices in a network
• Star topology


  • Devices connected to a central hub/switch
  • Hub repeats signals to all devices
  • Switch directs signals to correct recipient
  • Switch improves security and speed
  • Central device is a single point of failure
• Mesh topology


  • No central communication point
  • Multiple direct connections between devices
  • No single point of failure
  • Packets can take different paths from source to destination
• MAC address


  Unique 48-bit identifier for a network interface card
• Mesh topology


  • No critical point of failure as every communication path has several alternative pathways
  • Communication devices can self-configure and this allows the most efficient path to be used as messages will be passed over different paths depending on path load and reliability
  • The internet is a classic example of a mesh network
• Packet-switching in the internet

  1. Messages are broken into multiple packets

  2. Each packet can take a different path from source to destination

  3. At the end point, the packets are put back into order using a sequence number that is part of the packet's header information
• MAC address


  • A 48-bit value allocated by the network interface card manufacturer
  • The most common format for displaying a MAC address uses six sets of two characters separated by a colon or hyphen
• If a device has both wired and wireless connections, it will have two network interface cards, each with its own MAC address
• MAC addresses are unique, and cannot be changed, but they can be spoofed by forcing the operating system to report a different address
• IPv4 address


  32-bit addresses usually displayed as four sets of denary numbers separated by dots
• IPv6 address


  128-bit addresses usually displayed as eight sets of hexadecimal numbers separated by colons
• An IP address is made up of a network ID part that is the same for all devices on the network, and a host ID part that must be different
• Network types


  • Wired
  • Wireless
• Wired networks


  • Devices are connected through a network switch
  • Devices are cabled into switches using UTP cables
  • Cable speed depends on cable category and other network components
• Wireless networks


  • Based around a central wireless access point (WAP)
  • Subject to interference from other wireless devices and some building materials block radio waves
  • Connecting requires scanning for networks within range, entering a password, and data is encrypted
• Open wireless networks are not secure as data may not be encrypted
• Hybrid networks


  • Mix of wired and wireless connections
  • Wired for larger desktop computers and devices not often moved, wireless for mobile devices
• Wired vs wireless network comparison factors

  • Speed
  • Security
  • Range
  • Setup
  • Cost
• Standard


  Technical specification that specifies how software and hardware components must work
• Protocol


  Set of rules that determines how two devices will communicate
• OSI seven-layer model


  • Divides communications into seven layers with defined responsibilities and interfaces
• TCP/IP four-layer model


  • Combines physical and data link layers, and application/presentation/session layers