Network
Protocols

TCP/IP · HTTP/HTTPS · FTP · SMTP · DNS · Layers

CSZoneAQA GCSE Computer Science 8525

What is a Protocol?

Rules for Communication

A protocol is a set of agreed rules that govern how data is transmitted between devices on a network. Without protocols, different devices and manufacturers couldn't communicate — like two people speaking different languages.

Protocols define: data format, transmission speed, error checking, how connections start/end

Protocols are layered — each layer handles a specific job (TCP/IP model)

Key Protocols to Know

The Protocols AQA Expects

Protocol	Purpose
HTTP	Transfers web pages (HyperText Transfer Protocol)
HTTPS	Secure HTTP — data encrypted with SSL/TLS. Used for banking, shopping
FTP	File Transfer Protocol — uploads/downloads files between client and server
SMTP	Simple Mail Transfer Protocol — sends emails
IMAP/POP3	Receives emails. IMAP keeps on server; POP3 downloads to device
DNS	Domain Name System — translates domain names to IP addresses

TCP/IP and Packet Switching

How Data Travels Across the Internet

TCP/IP is the foundation of internet communication. Data is broken into packets, each with headers (source IP, destination IP, sequence number). Packets travel independently across the network and are reassembled at the destination. TCP checks for errors and requests retransmission of lost packets.

IP handles addressing and routing packets

TCP handles reliable delivery, ordering, and error correction

Exam Practice

Have a go at this question

AQA-style question

Explain why HTTPS is used instead of HTTP when making an online purchase.

2 marks

HTTPS encrypts the data being transmitted [1] using SSL/TLS, so that sensitive data such as credit card details cannot be intercepted and read by a third party [1].

Key Takeaways

What to Remember

Protocols = agreed rules for communication. Without them, devices can't talk.

HTTP/HTTPS = web · FTP = file transfer · SMTP = sending email

HTTPS = secure HTTP (encrypted with SSL/TLS)

DNS converts domain names (google.com) to IP addresses