1.3 computer network, connection and protocols

• Computer network


  Two or more computers or devices that are linked together, either using cables or wirelessly, so they can communicate and share resources
• LAN - Local Area Network


  • Devices connected together in a single building or site, such as a school, using ethernet and wireless connections
• WAN - Wide Area Network


  • Formed by connecting together LANs, spread across a wide geographic area, use third party telecommunications, largest WAN is the internet
• Bandwidth


  How much data can be transmitted over a network in a given period of time, measured in Mbps
• Factors affecting network performance

  • Number of users - available bandwidth is shared
  • Transmission media used - copper cables vs Wi-Fi
  • Error rate - data packet collisions
• Client-server network


  • All computers (clients) connected to a main server, backups/files stored centrally, activities managed centrally, if server stops all is stopped, servers are expensive
• Peer-to-peer network


  • All computers have equal status and are connected directly, computers store their own programs and files, no single point of failure, no central management or maintenance
• Network interface controller (NIC)


  Allows a device to communicate with a network, each NIC has a unique MAC address
• Transmission media


  • Copper wires, fibre-optic cables, radio waves for wireless
• Copper cables


  • Bandwidth generally 100Mb to 1Gb per second, for up to 100 metres, cost effective
• Fibre-optic cables


  • Very high bandwidth up to 100TB per second, can transmit data over 100km or more
• Radio waves


  • Used for wireless networking like Wi-Fi and Bluetooth, 2.4GHz and 5GHz frequencies, subject to interference and distance limitations
• Wireless access point (WAP)


  Hardware that connects to a network switch and allows Wi-Fi devices to connect to a network, broadcasts an SSID
• Network switch


  Hardware that allows multiple devices to connect together to form a wired network, stores MAC addresses and forwards data packets
• Router


  Hardware that connects networks of different types together, commonly used to connect a LAN to the internet, checks destination IP addresses and determines best transmission route
• Protocol


  Rules or standards that must be followed when data is sent between devices on a network
• Network protocols


  • Ethernet
  • Wi-Fi
  • Bluetooth
  • HTTP
  • HTTPS
  • FTP
  • POP
  • IMAP
  • SMTP
  • TCP
• Protocol layers


  • Each layer has a specific purpose to enable communication, data passes through each layer and is encapsulated, layers can be developed independently
• IP address


  Unique identifier assigned to every device connecting to the internet, IPv4 uses 32-bit numbers, IPv6 uses 128-bit numbers
• MAC address


  Unique 48-bit identifier for a network device, used to identify devices on a LAN
• Domain Name Server (DNS)

  Enables websites to be accessed via their domain name by linking it to the IP address
• The Cloud


  • Network of servers that store data, files and applications can be accessed from any internet-connected location, benefits include flexibility and reduced maintenance, drawbacks include reliance on internet and less control over security
• Network topology


  • The way devices are arranged and connected together
• Star network topology


  • Each computer connected to a central point like a switch or server, fast and reliable, easy to add new devices, but central point is single point of failure
• Mesh network topology


  • Every device connected to every other device, no single point of failure, can handle high data volumes, but impractical and expensive to set up