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AS Level Computer Science OCR 1.3.3 Networks, LAN vs WAN, Topologies -…

- - - - So, they can communicate and share resources.
    - - Allow computers to share resources
      - Allows computers to communicate with each other.
    - - Makes a computer more vulnerable to being attacked
- - - - Establish a connection
        
        Transfer data
        
        Release connection
    - - Telephone
      - Large scale data transfer
  - - - Data is broken down into segments (500 - 1500 bytes).
        
        Packed into datagrams for local delivery.
        
        Packed into packets ready for delivery across networks
        
        Packed into frames for delivery over a WAN.
    - - Are made up of the header and the payload and a footer.
        
        Header
        
        Recipient address
        
        So the packet knows where to go.
        
        Sequence order number
        
        So the recipient knows the order of the payloads.
        
        Senders IP
        
        So if another packet from the same file doesn't arrive the recipient know where to request it from.
        
        Time to Live
        
        So if the packet gets lost it will self destruct.
        
        The payload is the section of file being sent.
        
        The Footer contains an error check digit.
        
        If the packet is using odd parity.
        
        Then the check digit will be changed to make the number of 1s in the packet an odd number.
        
        If the packet is using even parity.
        
        Then the check digit is adjusted so there are an even number of 1s in the packet.
- - - - Very simple - no specialist OS needed.
      - No expensive complicated server needed.
      - No specialist staff needed.
      - No single point of faliure.
    - - Computers can get busy serving files to others.
        
        Slowing your machine down.
      - Not centralised.
        
        So no central management of backup.
      - Files shared by other users can be hard to find if different people organise differently.
      - Management is down to each user.
      - Little built in security.
      - No hot desking.
      - Each user responsible for their own back up.
  - - - All servers centralised for easier management and access.
      - Network peripherals controlled centrally.
      - Allows for hot desking.
      - Users can access shared data which is controlled centrally.
      - Backups and security is also controlled centrally.
    - - You need a server which is expensive.
        
        As well as staff to manage the network.
      - A special operating system is needed.
      - If the server fails the whole network fails.
      - Not easy to set up and run.
- - - - Manufacturers and engineers need to adhere to
  - - - How communications between devices are formatted and how they are sent and received
    - - They're reliable and robuts
    - - FTP
        
        File Transfer Protocol
        
        FTP is a protocol to download, upload and transfer files across the internet
        
        It can be used to communicate computer to computer
        
        Or through the cloud
        
        An internet connection is required to execute an FTP transfer
      - HTTP vs HTTPS
        
        HyperText Transfer Protocol (Secure)
        
        Is used to load websites using hypertext links
        
        Is used to encode and transfer information between clients and web servers
        
        Is the main protocol for information transmission across the internet
        
        HTTPS is encrypted this makes it slower that HTTP which is faster
      - SMTP
        
        Simple Mail Transfer Protocol
        
        Is a protocol to send and receive email
        
        It is often paired with a front-end protocol like POP or IMAP to allow users to see their mail
      - POP vs IMAP
        
        IMAP
        
        Is a protocol to allow clients to retrieve mail from a mail server
        
        Allows user to organise their emails
        
        Connects to the server every time to allow a user to see their emails on multiple devices
        
        Requires an internet connection
        
        Emails can be viewed on multiple devices
        
        Internet Message Access Protocol
        
        POP
        
        Every time there is a new email it is downloaded onto the device and deleted from the server
        
        Emails can only be seen on 1 device
        
        No need for an internet connection to view emails
        
        Post Office Protocol
      - TCP vs UDP
        
        TCP
        
        Transmission Control Protocol
        
        Is a protocol that allows programs and devices to communicate over a network
        
        It is designed to send packets over the internet and ensure their successful delivery
        
        TCP/IP Stack
        
        Layers
        
        Application Layer
        
        Provides the user with access to services and data provided over the network
        
        Specialist protocols deal with specific applications
        
        5 more items...
        
        Transport Layer
        
        Manages communication over the network
        
        Uses TCP to ensure communications are reliable
        
        1 more item...
        
        Internet Layer
        
        Every device on the internet has a unique IP address so data can be sent to it
        
        This layer is uses principally for routing
        
        It uses Internet Protocol to
        
        2 more items...
        
        Link Layer
        
        Manages the physical connection between devices
        
        Uses multiple different standards depending on the hardware used
        
        3 more items...
        
        Functional decomposition
        
        Consists of multiple layers
        
        The protocols used by the layers of the receiver and sender must be the same
        
        UDP
- - - - Non fibre signal to box is analogue on phone lines
        
        Signal in the box is converted to digital for fibre again
- - - - This means all the devices can communicate directly with one another.
        
        Without going through a switch or other devices
  - - - This still means all devices can communicate to all others.
        
        But they may need to go via another device to get there.