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J276/01 - Section 2 - Networks (Protocols (Other protocols you need to…

- - - - WANs may be connected using fibre or copper telephone lines, satellite links or radio links. The Internet is the biggest WAN.
- - - - The main advantage of a mesh topology is that there is no single point where the network can fail. If the central switch or server of a star network fails then the whole network fails - in a mesh network, if one device fails then the data is sent along a different route to get to its target.
      - The traditional problem with mesh networks has been that they were very expensive - you needed a lot of wire to connect so many devices together. But now more people are using wireless technology, mesh networks are a more practical option.
- - - - Layer 3 - Transport Layer. Controlling data flow - e.g. splitting data into packets and checking packets are correctly sent and delivered. Example is TCP.
        
        Layer 4 - Application Layer. Turning data into websites and other applications and vice versa. Examples include HTTP, FTP and SMTP.
    - - It breaks network communication into manageable pieces. This helps developers concentrate on only one area of the network without having to worry about the others.
        
        As layers are self-contained, they can be changed without the other layers being affected.
        
        Having set rules for each layer forces companies to make compatible, universal hardware and software, so different brands will work with each other and always work basically in the same way.
- - - - 3) The way data is sent changes depending on network traffic so the packets can take different routes. If a router receives too many packets at once it may prioritise some over others.
        
        4) As the packets take different routes, they can arrive in the wrong order. The receiving device uses the packet numbers to reassemble them in the right order.
        
        5) Sometimes packets go missing in transit so the receiving device checks periodically that all packets have been received. If it hasn't received them within a certain time, it sends a timeout message back to the sending device.
        
        6) If all the data is received and the checksums match, a receipt confirmation is sent to the sending device.
- - - - Pros
        
        Easier to install and update software
        
        Easier to manage network security
        
        Easier to preform back-ups
        
        Servers are very reliable and are always on
        
        Easier to keep track of files as they are stored centrally
      - Cons
        
        Server dependence - if the server goes down all clients lose access.
        
        The server may become overloaded if too many clients are accessing it at once.
        
        Expensive and needs a IT specialist to maintain.
  - - - Pros
        
        Easy to maintain - you don't need any expertise or expensive hardware
        
        No Dependence on server - if one device fails the whole network isn't lost
      - Cons
        
        Copying files between devieces creates duplicate files, its easy to lose track of whats stored.
        
        Peer machines are less reliable and data may be lost if one fails.
        
        No centralised management - devices need things installed individually. Backups are more complicated.
        
        machines are prone to slow when other devices access them.
- - - - Deleting or modifying files.
      - Scareware
      - Locking files - ransomware encrypts all computer files and the user receives a message asking them for a large sum of money to get the decryption key.
      - Spyware - secretly monitors user actions such as key presses.
      - Rootkits - alter permissions giving malware and hackers administrator-level access to devices.