Networks:

Networks:

1. Advantages:

   • Share files-sam files are available on different computers
   • Share resources-printers or internet connections
   • Prove a single username and password that can be used on every computer on the network

2. Disadvantages:

   • Expensive-extra hardware is needed
   • More room for error-if something goes wrong it can effect every computer
   • Requires a lot of technical expertiese

3. LAN:

   • A local area network confined to one location or organisation
   • Resources are only accessible by computers on the LAN

4. WAN:

   • A wide area network is a network of LANs spanning a wide area
   • Example: Internet

5. WIRED:

   • Computers are connected with physical wires
   • ELectrical pulses on the wire are used to transmit binary data

6. WIRELESS:

   • Radiowaves are used to transmit binary data
   • No physical connections needed

7. Topologies:

   • Collision
     • When two computers attempt to transmit on the same channel and the signals interfere and get corrupt.
   • Catastrophic failure:
     • when a fault is severe enough to prevent the entire network from functioning.
   • Ring Network:
     • Each computer is connected to two other computers in a ring formation. Each computer receives signals from one of its connected computers. The data travels around the ring in one direction until it reaches the intended recipient.
       • Advantages:
         • No collisions
         • Number of computers doesn't effect speed
       • Disadvantages
         • One fault cable or computer will result in catastrophic failure
         • Difficult to add new computers
   • Bus Topology:
     • A single cable connects all the computers. All the clients and servers connect to this cable. Terminators are connected to each end of the table.
       • Advantages:
         • Cheap
         • Easy to install
         • No extra equipment required
       • Disadvantages:
         • High chance of collisions
         • Damage to wires results in catastrophic failure
         • Only suitable for small networks
   • Star Network:
     • All computers are connected to a central hub or switch. A hub sends each message to all the other computers. A switch checks the address and sends it only to the correct one.
       • Advantages:
         • No collisions
         • Failure of a cable or computer isn't catastrophic
         • Easy to add new computers
       • Disadvantages:
         • Expensive
         • Failure of a hub/switch is catastrophic and difficult/expensive to fix
   • Mesh Topology:
     • Each computer is connected to one or more other computers. A full mesh has every other computer connected to every other computer. A partial mesh has only some of the computers connected.
       • Advantages:
         • Zeto catastrophic failure
         • Multiple transitions can happen simultaniously
       • Disadvantages:
         • Lots of unnecessary connections
         • difficult to maintain and administer

8. Pathfinding:

   • Circuit Switching:
     • The route is locked until the communication is complete
     • Other transmissions may be blocked for a long period of time if there are large transmissions
     • USed where real-time communication is needed
   • Packet Switching:
     • Data is split into chunks called packets and are sent independently using different paths
     • The packets will arrive in a different order to which they were sent in
     • each packet is numbered so it can be reassembled in the right order
   • Routing:
     • Each node continuously tests its connections and assigns them a "cost"
       • Route-finding algorithms are used to determine which route through the mesh will have the lower cost
       • The cost changes as nodes become more or less busy so new routes are needed

9. Protocols:

   • HTTP:
     • Hyper Text Transfer Protocol is the standard protocol used for requesting an HTML file from a webserver
   • HTTPS:
     • A secure version of HTTP which encrypts the data before sending it so that it can't be intercepted along the way
   • POP3:
     • Post Office Protocol 3 is a protocol for downloading email from a mail server. It is an old protocol which only delivers the email
   • SMTP:
     • Simple Mail Transfer Protocol is the protocol for uploading email to a mail server.
   • IMAP:
     • Internet Message Access Protocol replaced POP3 when web-based email took off.
     • It is for reading email from a mail server, but doesn't require the mailto be downloaded.
     • Allows emails to be left on the server and read from different mail readers.
   • FTP:
     • File transfer protocol is a protocol for transferring files between two computers. It is commonly used by web developers for uploading their HTML files to their websereves

10. TCP/IP Stack:

    • Application:
      • Provides applications services to users and programs.
    • Transport:
      • Handles data-consistency functions (error checking)
    • Network
      • Provides network addressing and routing (IP address)
    • Data Link:
      • Prepares and corrects data to be passes to the physical layer.
    • Physical:
      • Transmits and receives bits

11. IP Addresses:

    • IPv4:
      • There are more than 4.2 billion devices on the internet, so there aren't enough IP addresses to assign one to each device
    • IPv6:
      • While IPv4 is still the main system used on the internet, there is a new version called IPv6
      • Uses a 128 bit address
    • DNS:
      • DNS is a system used to store Domain Names and look up their IP addresses.