Protocols, Layers and the Internet
Why we need protocols
A protocol is a set of rules that lets devices communicate. Both devices must follow the same rules for data to be sent, received and understood correctly. The internet relies on many protocols working together in layers.
Common protocols you must know
| Protocol | Used for |
|---|---|
| TCP (Transmission Control Protocol) | Splits data into packets and reassembles them in order; checks for errors |
| IP (Internet Protocol) | Addresses and routes packets between networks |
| HTTP (HyperText Transfer Protocol) | Requesting and sending web pages |
| HTTPS | HTTP with encryption (secure web traffic) |
| FTP (File Transfer Protocol) | Transferring files between computers |
| SMTP (Simple Mail Transfer Protocol) | Sending email |
| IMAP (Internet Message Access Protocol) | Retrieving email (kept on the server) |
TCP/IP is the name for the whole set of protocols that make the internet work.
Packet switching
Data sent over a network is broken into small chunks called packets. Each packet contains:
- the data (payload);
- the sender and recipient addresses;
- a packet number (so they can be reassembled in the right order);
- error-checking information.
Packets can take different routes across the network and are reassembled at the destination. If a packet is lost or corrupted, it can be resent — this makes the network efficient and resilient.
Network layers
Protocols are organised into layers, where each layer does a specific job and works independently of the others. A common 4-layer model:
| Layer | Job | Example protocols |
|---|---|---|
| Application | Provides services to the user/programs | HTTP, HTTPS, FTP, SMTP |
| Transport | Splits data into packets, checks errors, reassembles | TCP |
| Network (Internet) | Adds addresses and routes packets | IP |
| Link | The physical hardware and connection | Ethernet, Wi-Fi |
Why use layers?
- Breaks a complex task into manageable parts.
- Each layer can be developed or changed independently without affecting the others.
- Makes it easier for different manufacturers' hardware/software to work together (standardisation).
The internet vs the World Wide Web
- The internet is the global network of networks (the infrastructure).
- The World Wide Web (WWW) is the collection of websites and web pages accessed over the internet using HTTP(S). They are not the same thing.
Worked example
Which two protocols work together to break a message into packets and route them to the right place?
- TCP splits the data into packets and reassembles them; IP addresses and routes them. Together: TCP/IP. ✓
Common mistakes
- Mixing up SMTP (send email) with IMAP (retrieve email).
- Saying the internet and the World Wide Web are the same thing — they aren't.
- Forgetting that packets can take different routes and be reassembled in order.
Exam tips
- Learn the protocol table — "which protocol for X" is a very common 1-mark question.
- For "why use layers", give two reasons (manageable parts + independent development/standardisation).
- Remember HTTPS = HTTP + encryption for secure sites.
Key facts to remember
- A protocol is a set of rules for communication; TCP/IP underpins the internet.
- Packet switching: data split into addressed, numbered packets that route separately and reassemble; lost packets are resent.
- Layers (Application, Transport, Network, Link) split the job up so parts can be developed independently.