Network Protocols

• Networks need protocols to set the rules
• A network standard is a set of agreed requirements for hardware and software
• Network standards are important as they allow manufacturers to create products and programs that will be compatible with products and programs form other manufacturers
• A network protocol is a set of rules for how devices communicate and how data is transmitted across a network
• Communication protocols specify how communication between 2 devices must start and end, how the data must be organised, and what the devices must do if data goes missing
• Communication on the same network uses MAC addresses
• Every device needs a unique identifier so it can be found on a network
• MAC addresses are assigned to all network-enabled devices by the manufacturer. They are unique to the device and cannot be changed
• MAC addresses are 48 or 64-bit binary numbers (i.e. a long string of 48 or 64 0s and 1s). To make them easier to use they're converted into hexidecimals
• 10011000 10000001 01010101 11001101 11110010 00101111 = 98-81-55-CD-F2-2F

  This binary MAC address is translated into 6 hex numbers
• MAC addresses are mainly used by the Ethernet protocol on LANs. LAN switches read the MAC addresses and use them to direct data to the right device
• Communication between different networks uses IP addresses
• IP addresses are used when sending data between TCP/IP networks, e.g. over the internet
• IP addresses are assigned either manually or automatically before the device can access the network
• There are 2 versions of IP addresses - IPv4 (which uses 32 bits) and IPv6 (which uses 128 bits)
• IPv6 was created due to the increasing number of devices that need unique IP addresses. IPv4 has 2^32 (over 4 billion) IP addresses, whereas IPv6 has 2^128 addresses
• IPv6 addresses are split into 16-bit chunks and each one is given as a hex number
• IPv4 addresses are split into 8-bit chunks and each one is given as a denary number
• TCP/IP is the most important protocol
• TCP/IP is the protocol which dictates how data is sent between networks (e.g. over the internet). It's made up of 2 protocols:

  • Transmission Protocol Control (TCP) sets the rules for how devices connect on the network. It's in charge if splitting data into packets and reassembling the packets back into the original data once they reach the receiving device. It's also reponsible for checking the data is correctly sent and delivered
  • Internet Protocol (IP) is responsible for directing packets to their destination across the network
• HTTP - Hyper Text Transfer Protocol

  • Used by web browsers to access websites and communicate with web servers
• HTTPS - Hyper Text Transfer Protocol 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's 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
• Network protocols are divided into layers
• A layer is a group of protocols which have similar functions
• Layers are self-contained - protocols in each layer don't need 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. So in the example 4-layer model below, when you send an email (on layer 4), this triggers actions in layer 3, all the way down to layer 1

  
• Data can only be passed between adjacent layers
• Advantages of 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 standards 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