computer networks

• How does the school connect all these devices together?

  By wires (Ethernet cables or fibre optic cables) or wirelessly (wifi)
• WANs connect several networks over a large geographical area (eg several buildings/towns/cities, countries) using telephone lines, satellites and radio waves
• The server also connects to the switch.  The server is a powerful computer on the network which stores all the network software and all of the user’s data files

  The switch is responsible for directing the data traffic from one device on the network to another in the most efficient route.

  (in a star network)
• Advantages of a mesh network:

  •  No single point of failure – it is resilient
  • Expansion and modification can be done easily wirelessly without disrupting the network
  • Data can be transmitted from different devices simultaneously
• Disadvantages of a mesh network:


  • Can involve redundant connections
  • Expensive to install cabling if using wired connections
  • Network maintenance and administration is difficult
• ‘Ethernet’ refers to a set of network standards or protocols (rules which define how devices communicate on a network).


  It describes how devices should format data ready for transmission between computers on the same network
• Ethernet cable is the standard cabling used on LANs
• Transmission media is the way that communication is sent through the network
• Transmission media:

  Ethernet cable, fibre optic cable, Wi-Fi/wireless/microwaves, coaxial cable, copper cable
• A client is a computer or device which requests the services or resources provided by the server
• Examples of servers

  • Web server stores (“hosts”) websites
  • Email server stores emails centrally and manages email requests
  • Print server handles printing requests
  • File server stores and manages user files centrally
• A file server holds all the users’ data files, software and manages backups
• A print server may organise printing on different printers
• An email server may receive emails, detect and block spam, distribute emails to users
• A web server may host the school’s external website
• A database server may hold student records or other databases
• Advantages of a client-server

  • With file servers, all of the files are stored in one place and can be backed up centrally.  
  • Files can be accessed from any computer, as they are not stored locally (on individual machines)
  • Email servers provide a central storage for emails that can be accessed from different devices
  • A print server can manage all files to be printed. This allows one printer to be shared by many computers.  Manages print queue.
• A peer-to-peer network has no central server


  All of the connected devices are equal in status (hence “peers”).
• Advantages of a peer-to-peer network

  • Easier to set up – computers can simply be cabled together
  • No need for dedicated server equipment - saves money
  • Individual computers can share a printer, router, modem and other hardware
  • Users can communicate directly with each other and share each others’ files
• Disadvantages of a peer-to-peer network:

  • Viruses and malware are more easily transferred as there is no central firewall to manage security
  • Data recovery and backup is not done centrally, so each user has to take responsibility for own files
  • Files are stored on individual computers and may be hard to locate if the computer’s owner does not have a logical filing and naming system
  • If a computer is broken or switched off, data on that machine cannot be retrieved from other machines
• Web hosting is the term given to storing a website on a central web server.


  It is a service offered by companies to host web pages and files for other companies/users
• Examples of transmission media

  • Copper cable
  • Fibre optic cable
  • Wi-Fi
• Bandwidth is the amount of data that can be carried through a connection at a time
• Connection speeds are measured in Mbps (Megabits per Second)
• Latency refers to the delay between sending data and it being received
• The internet is a global network of networks (LANs and WANs)
• IPv4 addresses use four 8-bit numbers (0-255) separated by dots
• Packet switching describes the way data is transferred from one location to another across the Internet
• During packet switching, the file is broken up into packets
• Each packet is labelled up in a “header” containing

  • The recipient’s IP address 
  • The sender’s IP address
  • The sequence number of the packet e.g. 1 of 240
  • The number of packets in the whole communication
  • Error checking data
• The packets flow through the Internet via different routes to their destination IP address
• Each packet is marked with the packet number so that the packets can be reassembled in the right order by the receiving device
• • The recipient computer re-orders the packets into the correct order
  • Each packet is checked for errors
  • Corrupt packets are requested to be resent
• Points on a network diagram are called nodes
• All websites must be hosted on a web server.  A web server will have a fixed/static IP address.
• These are a set of wifi standards/protocols.  Wifi uses radio waves and operates at two radio frequencies, 2.4GHz and 5GHz.
• Advantage of 2.4GHz wi-fi: Greater range and coverage


  Disadvantage: More interference from other devices as this is a crowded frequency
• Advantage of 5GHz wi-fi: Less crowded and higher data transmission rates


  Disadvantage: Less able to penetrate through walls
• Plaintext: the original message to be encrypted
• Ciphertext: the encrypted message