Network Protocols — Internet and Networking | IGCSE Computer Science

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 7% of your exam marks.

stable

Low

Stable7%

Network topologies, protocols (HTTP, TCP/IP, FTP, DNS) and network hardware appear consistently.

A protocol is a set of rules that govern how devices on a network communicate with each other.

Without a protocol, two computers could send data but neither would understand what the other was sending. Protocols define the format of packets, the order of messages, error handling, and many other details.

The CIE syllabus names a small set of protocols you should know.

TCP/IP (Transmission Control Protocol / Internet Protocol)

TCP/IP is the foundational protocol suite of the internet. TCP splits data into packets and reassembles them; IP routes the packets between networks.

IP is responsible for addressing and routing. Every packet has a source IP and a destination IP, and routers use the destination IP to forward it.
TCP is responsible for reliable delivery: splitting data into packets at the sender, putting them back together in order at the receiver, detecting lost or corrupted packets, and requesting re-transmission (using ARQ, topic 5).

Almost every other internet protocol (HTTP, HTTPS, FTP, SMTP) runs on top of TCP/IP.

HTTP and HTTPS

HTTP (Hypertext Transfer Protocol) is the protocol used by web browsers to request web pages from web servers and receive the response.

HTTP defines how the browser asks for a page (a GET request) and how the server replies (with the HTML content).
HTTP is not encrypted: any data sent through it can be read by anyone who intercepts the traffic.

HTTPS (Hypertext Transfer Protocol Secure) is HTTP with encryption added on top, using TLS/SSL.

HTTPS works the same way as HTTP but the data is encrypted in transit.
A passive eavesdropper sees only ciphertext.
All modern websites use HTTPS, particularly any site that handles passwords, payments or personal information.

The lock icon in the browser's address bar indicates HTTPS is in use.

FTP (File Transfer Protocol)

FTP is a protocol used for transferring files between a client and a server over a network.

Used to upload or download files (e.g. publishing a website to a hosting server).
Has a secure variant, SFTP, that adds encryption.

POP3 and IMAP (email retrieval)

POP3 and IMAP are protocols used by email clients to receive messages from an email server.

POP3 (Post Office Protocol v3): downloads emails to the local device and (by default) deletes them from the server. Older protocol.
IMAP (Internet Message Access Protocol): keeps emails on the server and syncs across multiple devices. Used by almost all modern email apps.

SMTP (Simple Mail Transfer Protocol)

SMTP is the protocol used to send emails from a client to a server, and between mail servers.

POP3/IMAP pull emails down; SMTP pushes them out. The pair work together to deliver a message from sender to recipient.

The common protocols at a glance

Protocol	Used for
TCP/IP	The core transport and addressing layer that everything else runs on
HTTP	Web browsing (unencrypted)
HTTPS	Web browsing with encryption
FTP	File transfer between client and server
SMTP	Sending email
POP3	Retrieving email (older, downloads and deletes from server)
IMAP	Retrieving email (modern, keeps emails on server)

Why protocols matter

Protocols are what make the internet work as one giant network rather than many incompatible private systems. A web browser written in California can read a website hosted in Singapore because both ends speak the same HTTPS/TCP/IP protocols. The two sides do not need to know anything about each other except that they both follow the same agreed rules.