Standards, Protocols and Layers

• What are protocols?

  A set of rules for how devices communicate over a network
• Network Protocols- Layers

  A group of protocols that have similar functions
• Layers are self contained.
• Layering allows standards to be put in place and simply adapted as new hardware and software is developed.
• Application layer - encodes/decodes the message in a form that is understood by the sender and the recipient.
• Transport layer - breaks down the message into small chunks (packets). Each packet is given a packet number and the total number of packets. The recipient uses this information to assemble the packets together in the correct order. It also allows the recipient to see if there are any missing packets.
• Network layer - adds the sender’s IP address and that of the recipient. The network then knows where to send the message, and where it came from.
• Link layer - enables the transfer of packets between nodes on a network, and between one network and another.
• A protocol is a set of rules that governs transmission of data.
• Many types of protocol exist, but the ones that govern addressing are:

  • Internet Protocol (IP) addressing
  • media access control (MAC) addressing
• A MAC address is a unique serial number assigned to each network interface controller (NIC)
• The MAC address is assigned by the NIC’s manufacturer and cannot be changed.
• TCP/IP - Transmission Control Protocol/Internet Protocol - enables communication over the internet.
• HTTP and HTTPS - Hypertext Transfer Protocol - governs communication between a webserver and a client. HTTPS (secure) includes secure encryption to allow transactions to be made over the internet.
• FTP - File Transfer Protocol - governs the transmission of files across

  a network and the internet.
• SMTP - Simple Mail Transfer Protocol - governs the sending of email over a network to a mail server.
• POP3- Post Office Protocol- 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 delete it- you only download a copy. Used by most web-based email clients.
• Why are standards uses in computing?

  The principle of a standard provide rules for areas of computing. Standards allows hardware/software to interact across different manufacturers/producers.
• TCP/IP is  made up of loads of smaller protocols which are joined together to make one larger protocol. This is done as communication on the internet is very complex and constantly changing.

  The smaller sections of the TCP/IP stack are called layers.

  In GCSE these layers are:

  • Application
  • Transport
  • Network
  • Link
• Why are layers used?

  As each layer has a specific purpose this means it's easy to update and fix as it will not affect other layers.

  Additionally it is more robust as if one layer does not correctly work it will not affect any of the other layers and will be easier to solve.
• Which protocol would you use? - Uploading a high-resolution image to a cloud server

  FTP
• Which protocol would you use? - Viewing their online portfolio in a web browser

  HTPP
• Which protocol would you use? - Sending a large file to a print service

  FTP
• Which protocol would you use? - Receiving an email from a client

  POP / IMAP
• Which protocol?- Requesting a webpage from a web server

  HTTP / HTTPS
• Which protocol?- Entering a username and password to access their bank account

  HTTPS
• Which protocol?- Downloading a text document from a web server

  FTP / HTTP / HTTPS
• Which protocol?- Checking for new emails in their inbox

  IMAP / POP
• Some protocols have layers. Why?

  • Layers are not reliant on other layers
  • One layer can be changed without affecting the others
  • Separates tasks so they can be developed independently
  • A developer can focus on only one layer
  • Allows for standards for individual layers to be developed
  • Manufacturers can develop hardware to fit into one particular layer
  • To group together similar protocols