4.1.6 Network protocols
What Is a Protocol?
A network protocol is a set of rules that governs how data is transmitted between devices on a network. Protocols define the format of data, the method of addressing, error handling and the order of communication — ensuring that devices from different manufacturers, running different operating systems, can communicate reliably.
Without agreed protocols, a message sent by one device would be unintelligible to another. Protocols are the "language" devices use to talk to each other.
General Network Protocols
Ethernet (IEEE 802.3) is the dominant wired LAN protocol. It defines how data is formatted into frames, how devices share a wired medium, and how MAC addresses are used to identify devices on the local network. Modern Ethernet supports speeds from 100 Mbps to 100 Gbps.
Wi-Fi (IEEE 802.11) is the wireless equivalent of Ethernet — it defines how data is transmitted over radio waves in a local area. Wi-Fi versions (802.11a/b/g/n/ac/ax, also known as Wi-Fi 4/5/6) have progressively increased speeds and range.
- Both operate at the link layer — local device-to-device communication within a network
- Both use MAC addresses to identify devices at this level
TCP/IP (Transmission Control Protocol / Internet Protocol) is the foundational protocol suite of the internet. It governs how data is broken into packets, addressed, transmitted and reassembled across interconnected networks.
- IP (Internet Protocol): handles addressing and routing — assigns IP addresses and determines the path packets take through the network
- TCP (Transmission Control Protocol): handles reliable delivery — breaks data into packets, numbers them, and ensures they all arrive correctly at the destination (requesting retransmission of any lost packets)
- TCP/IP is used by virtually all internet communication: web browsing, email, file transfer
HTTP (Hypertext Transfer Protocol) is the protocol used to transfer web pages between a web server and a browser. When you type a URL into your browser, it sends an HTTP request to the web server, which responds with the HTML content of the page.
HTTPS (HTTP Secure) is HTTP with encryption added via TLS (Transport Layer Security). All data exchanged between the browser and server is encrypted, preventing eavesdroppers from reading it. HTTPS is essential for:
- Online banking and shopping (protecting payment details)
- Login pages (protecting passwords)
- Any page that handles personal data
Browsers display a padlock icon for HTTPS connections. Sites still using plain HTTP are flagged as "Not Secure" by modern browsers.
FTP (File Transfer Protocol) is a protocol specifically designed for transferring files between a client and a server. It allows a user to upload files to a remote server and download files from it.
- Used by web developers to upload website files to a web hosting server
- Supports authentication (username and password)
- Standard FTP sends data in plaintext — SFTP (Secure FTP) or FTPS add encryption for secure file transfers
Email Protocols
| Protocol | Full name | Purpose |
|---|---|---|
| SMTP | Simple Mail Transfer Protocol | Sending email — used to send an email from a client to an email server, and between email servers. SMTP is for outgoing mail only. |
| POP3 | Post Office Protocol v3 | Receiving email — downloads emails from the server to the local device and typically deletes them from the server. Suited to one device; emails not accessible from multiple devices. |
| IMAP | Internet Message Access Protocol | Receiving email — emails remain on the server; the client synchronises with the server. The same messages are accessible from multiple devices (phone, laptop, tablet). The modern standard for most email services. |
POP3 vs IMAP at a glance
POP3: downloads and removes from server → one device, offline access. IMAP: reads from server without removing → multiple devices, server-side storage. Most modern email clients (Gmail, Outlook) use IMAP.
Key Takeaways
- A protocol is a set of rules governing how devices communicate.
- Ethernet / Wi-Fi: local network connection (wired / wireless).
- TCP/IP: internet addressing and reliable packet delivery.
- HTTP / HTTPS: web page transfer (HTTPS adds encryption).
- FTP: file transfer between client and server.
- SMTP: sending email; POP3: receiving (downloads, removes); IMAP: receiving (server-side, multi-device).