Network protocols

The essentials

A protocol is a set of rules that devices follow to communicate, covering the format of data, how it is sent, and how errors are handled. Without common protocols, devices made by different companies could not understand each other.

Key points

• HTTP (HyperText Transfer Protocol): used to transfer web pages between a web server and a browser. It works on a request–response model: the browser sends a request and the server sends a response. HTTP is stateless (each request is independent).
• HTTPS: HTTP with encryption (using SSL/TLS), so data cannot easily be read if intercepted.
• FTP (File Transfer Protocol): used to transfer files between computers, for example uploading website files to a server.
• IP (Internet Protocol): gives addresses to devices and routes packets from source to destination across networks.
• TCP (Transmission Control Protocol): breaks data into packets, makes sure they all arrive, and puts them back in the right order. TCP and IP together are called TCP/IP.
• PPP (Point-to-Point Protocol): used to connect two directly connected nodes, such as a computer and an Internet service provider over a telephone line.
• SMTP (Simple Mail Transfer Protocol): used to send email from a client to a mail server and between mail servers.
• POP3 (Post Office Protocol 3): downloads email from the server to the user's device, usually removing it from the server.
• IMAP (Internet Message Access Protocol): lets users read and manage email kept on the server, so it stays in sync across several devices.

Exam tips

• Email: SMTP sends; POP3 and IMAP receive.
• Match each protocol to its job in a single phrase.

Common mistakes

• Saying SMTP is used to read mail from the server.
• Saying IP ensures packets arrive in order; that is TCP's job.