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Network characteristics - Coggle Diagram

- - - - Topmost layer in the Four Layer Model. It holds protocols that govern how data moves in and out of applications. These include web browsers (the HTTP protocol), email applications (POP and SMTP) and servers (FTP)
        Only interact with the protocols in the Transport layer.
        When it receives data, it presents it in the form it was sent.
    - - Contains protocols that govern the transport of data packets across a network, e.g. TCP.
        It provides services for both 'connection mode' and 'connectionless' transmissions.
        Connection mode: there is a 'session' set up between devices that is maintained until the connection is dropped. TCP uses connection mode.
        Connectionless mode: The transmitter just sends its packets without setting up a session.
        The transport layer handles any error checking present.
        The transport layer interacts with the application layer above it and the Internet layer below it.
        Establishes an end-to-end connection between the source and recipient computers. It splits up the data into packets.
        When it receives data,it removes the port number and reassembles the packets.
    - - Contains protocols that govern how messages are prepared before they are sent, and how they are unpackaged after they are received. Example of a protocol IP (Internet Protocol). Adds the source and destination IP addresses.
        Outgoing messages: Internet or IP layer is responsible for preparing messages (datagrams) for transmission. This layer talks to the data link layer below it.
        Incoming messages: It checks the destination address of each packet and if it matches its own address it passes the
        packet up to the transport layer. If it does not match, then packet is ignored. When it receives data, it removes the IP addresses.
    - - Adds the MAC addresses to the packet. Responsible for handling the physical connection to the network.
        Ethernet is a physical protocol that defines the hardware performance expected and software in terms of the data format for a network.
        The three main functions of the Data link layer:
        
        To regulate the flow of data off and on the physical medium
        
        To deal with transmission errors
        
        Provide an interface between the physical medium and layer 2.
        When it receives data, it removes the MAC addresses.
- - - - Inefficiency of circuit switching led to "packet switching" - method of communicating packets of data across a network.
        Packet switching involves breaking the message into smaller parts which are sent individually through the network and are re-assembled on the other side.
        The TCP/IP protocol stack was developed. This sets out the rules for handling datagrams at each stage in their journey.
        Packets are given a 'packet number' to identify the order they're in.
        Packets will travel across the network, usually in different directions, taking the shortest route available at that instant.
        When the individual packets arrive at their destination they are reassembled into the complete message.
        With the TCP protocol, once all of the packets have safely arrived an acknowledgment message is sent to the original computer as confirmation.
        If a packet is missing or corrupted then the receiver sends a request for that particular packet to be resent.
    - - Benefits:
        
        Robust - If one router fails or goes offline, there is usually another path available.
        
        Efficient - Make efficient use of connections compared to circuit switching because each path is used for a short time by a packet and then becomes available for other packets. Data can be sent even when the network has a lot of traffic.
        
        Resilient - If a circuit switched network goes down for a moment, the whole message is lost. But with packet switching, only the packets that are lost need to be re-sent.
        
        Error correction - Each packet carries its own error correction codes, so if a few bits are corrupted, they can most likely be corrected.
        
        Multiple methods to ensure data arrives correctly.
        
        Transfers packets over a large network.
        
        Issues:
        
        Latency - Packets travel along random paths, no guarantee that they will arrive within a certain time period. Delay is called 'latency'. This can be a problem if you need the data quickly. Circuit switching doesn't have this problem since the connection is unbroken.
        
        Random arrival order - Packets arrive in random order, so they have to be re-assembled. If a packet is missing, this has to be re-sent to complete the message.
        
        Time is spent deconstructing and reconstructing the packets.