1.5 Network Protocols and layers

1.5 Network Protocols and layers

1. Layers - A layer is a group of protocols which have similar functions. Layers are self-contained - protocols in each layer do their job without needing to know what's happening in other layers. Each layer serves the layer above it - it does the hidden work needed for an action on the layer above.

   • Layer 1 Data link layer
     • Passing data over the physical network. responsible for how bits are sent as electrical signals over cables, wireless and other hardware
   • Layer 2 Network layer
     • making connections between networks, directing data packets and handling traffic. used by routers.
   • layer 3 Transport layer
     • Controlling Data flow e.g. splitting data into packets and checking packets are correctly sent and delivered.
   • layer 4 Application Layer
     • Turning data into websites and other applications and vice versa.
   • Advantages of using layers
     • 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 in basically the same way.

2. TCP/IP is the protocol which dictates how data is sent between networks e.g over the internet. It is made up of two protocols. Transmission Control protocol (TCP) sets the rules for how devices connect on the network. It's in charge of splitting the data into packets and reassembling the packets back into the original data once it reaches the receiving device. It is also responsible for checking the data is correctly sent and delivered.

3. Internet protocol (IP) is responsible for packet switching

4. Several other protocols build upon TCP/IP to do specific internet - based tasks

   • HTTP
     • Hyper Text Transfer Protocol
       • used by web browsers to access websites and communicate with web servers
   • HTTPS
     • HTTP secure
       • A more secure version of HTTP. Encrypts all information sent and received.
   • FTP
     • File Transfer Protocol
       • used to access, edit and move files between devices on a network, e.g. to access files on a server from a client computer
   • POP3
     • Post Office protocol version 3
       • used to retrieve emails from a server. The server holds the email until you download it, at which point it is deleted from the server
   • IMAP
     • Internet Message Access Protocol
       • used to retrieve emails from a server. The server holds the email until you actually delete it - you only download a copy. used by most web - based email clients
   • SMTP
     • Simple Mail Transfer Protocol
       • Used to send emails. Also used to transfer emails between servers.

5. Data Packets

   • 1) Data sent between networks e.g. on the internet using TCP/IP is split into equal-size packets.
   • 2) Every data packet has a header - this contains the control information. The control information is like the envelope of a letter - it includes the packet's destination address, the source data and the packet number.
   • 3) The data packet's payload is like the letter inside the envelope - it's the thing a person is likely to read, and the whole reason the data packet has been sent in the first place. The payload might be a part of an email, document, web page or streamed video.
   • 4) Packets are also likely to include, a checksum number - a form of validation used to check the payload data hasn't been corrupted during transit. The sending and receiving devices both calculate a checksum value by performing a function on the payload data. If the values match then the data has been received correctly.
   • Packet Switching
     • packet switching is used by routers to direct data packets on the internet and other IP networks.
     • 1) The sending device splits the data into packets to be sent across the network. Each packet is given a packet number to show the order of the data.
     • 2) Each router reads the packet header and decides which way to send the packet next, according to the IP address.
     • 3) The way the 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 priotritise some over others