📡 Paper 1 · 1.2 Communication and Internet Technologies
1.2.4 Internet Protocols (HTTP, FTP, SMTP)
Cambridge 9618 · International A Level Computer Science · ~14 min read
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What is a Protocol?
A protocol is a set of agreed rules that govern how data is transmitted between devices. Protocols define the format of data, the speed of transmission, error checking, and how connections are established and terminated.
HTTP and HTTPS
HTTP (HyperText Transfer Protocol) is the protocol used for transferring web pages (HTML documents) between a web server and a browser.
Client (browser) sends a request to the server (e.g. GET /index.html)
Server responds with the resource and an HTTP status code (e.g. 200 OK, 404 Not Found)
HTTP is stateless — each request is independent; the server doesn't remember previous requests
Default port: 80
HTTPS (HyperText Transfer Protocol Secure) is HTTP encrypted using TLS/SSL.
Data is encrypted between browser and server — prevents eavesdropping and man-in-the-middle attacks
Default port: 443
Required for any site handling sensitive data (logins, payments)
FTP — File Transfer Protocol
FTP is used to transfer files between a client and a server over a network.
Uses two connections: control connection (port 21) for commands, data connection (port 20) for file transfer
Supports uploading, downloading, renaming, and deleting files
Standard FTP is not encrypted — credentials sent in plaintext
SFTP (SSH File Transfer Protocol) and FTPS are secure variants
Used by web developers to upload files to web hosting servers
Email Protocols: SMTP, POP3, IMAP
SMTP — Simple Mail Transfer Protocol
Used to send email from a client to a mail server, and between mail servers
Port: 25 (between servers) or 587 (client to server with authentication)
Push protocol — the sending client pushes mail to the server
POP3 — Post Office Protocol version 3
Used to retrieve email from a mail server to a client
Downloads emails to the local device and (by default) deletes them from the server
Port: 110
Good for users accessing email from one device only
IMAP — Internet Message Access Protocol
Also used to retrieve email — but emails remain on the server
Allows access from multiple devices — emails are synchronised
Port: 143
Better for users accessing email on multiple devices (phone, laptop, tablet)
Protocol
Purpose
Default Port
Notes
HTTP
Web page transfer
80
Unencrypted
HTTPS
Secure web transfer
443
TLS/SSL encrypted
FTP
File transfer
20 (data), 21 (control)
Not encrypted by default
SMTP
Sending email
25 / 587
Between mail servers or client to server
POP3
Receiving email
110
Downloads and removes from server
IMAP
Receiving email
143
Emails stay on server — multi-device
Exam tip: Cambridge questions often ask you to identify which protocol is used for a given task, or compare POP3 and IMAP. Key distinction: POP3 downloads and (by default) deletes from server — suitable for one device; IMAP leaves on server and synchronises — suitable for multiple devices. Also know that SMTP sends, while POP3/IMAP receive.
⚠️ Common Mistakes
Confusing SMTP (send) with POP3/IMAP (receive)
Saying FTP is always secure — standard FTP sends credentials in plaintext; SFTP/FTPS are secure variants
Confusing HTTP port 80 with HTTPS port 443
Saying POP3 and IMAP both delete emails from the server — POP3 does by default; IMAP leaves them on the server
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Worksheet — 1.2.4 Internet Protocols
8 questions · instantly marked · Cambridge 9618 standard
Q1Define the term 'protocol' in the context of computer networks.[2]
✅ Mark scheme
Mark scheme
A set of agreed rules [1] that govern how data is transmitted/communicated between devices on a network [1]; defining the format, speed, error handling, and connection procedures.
Q2Explain the difference between HTTP and HTTPS.[3]
✅ Mark scheme
Mark scheme
HTTP transfers web pages between browser and server [1]; HTTPS is HTTP with TLS/SSL encryption [1]; HTTPS encrypts data in transit — preventing eavesdropping and protecting sensitive data such as passwords and payment details [1].
Q3Explain why FTP uses two separate connections and state what each is used for.[3]
✅ Mark scheme
Mark scheme
FTP uses a control connection (port 21) for sending commands (login, list directory, delete) [1]; and a separate data connection (port 20) for transferring file data [1]; keeping them separate allows commands to continue being received even during a file transfer [1].
Q4Compare POP3 and IMAP as email retrieval protocols. State which is more suitable for a user who accesses their email on three different devices.[4]
✅ Mark scheme
Mark scheme
POP3 downloads emails to the local device and by default deletes them from the server — emails only accessible on one device [1]; IMAP leaves emails on the server and synchronises across devices [1]; IMAP is more suitable for a user with three devices [1] — because emails remain on the server and appear consistently on all three devices [1].
Q5State the protocol and default port used for each of the following: (a) sending an email from a client to a server, (b) viewing a secure web page.[4]
✅ Mark scheme
Mark scheme
(a) SMTP [1]; port 587 (or 25 for server-to-server) [1]; (b) HTTPS [1]; port 443 [1].
Q6A web developer needs to upload website files to a remote hosting server. State which protocol they would use and explain one security concern with the standard version.[3]
✅ Mark scheme
Mark scheme
FTP (File Transfer Protocol) [1]; standard FTP does not encrypt data — usernames and passwords are sent in plaintext [1]; this means an attacker who intercepts the connection could read the credentials and gain access to the server [1].
Q7Explain what is meant by saying HTTP is 'stateless'.[2]
✅ Mark scheme
Mark scheme
HTTP is stateless meaning the server does not retain any information about previous requests [1]; each request from a client is treated independently as if it is the first request [1] — cookies/sessions are needed to maintain state.
Q8Explain the role of SMTP in sending an email from alice@example.com to bob@school.ac.uk.[3]
✅ Mark scheme
Mark scheme
Alice's email client uses SMTP to push the email to her outgoing mail server (example.com) [1]; example.com's mail server then uses SMTP to forward the email to school.ac.uk's mail server [1]; Bob's mail client then retrieves the email from school.ac.uk's server using POP3 or IMAP [1].
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Mini Test — 1.2.4 Internet Protocols
10 questions · 10 marks · 10 minutes
⏱ 10:00
10 marks
Section A — Multiple Choice [5 marks]
Q1Which protocol is used to send email?
Q2Which port does HTTPS use by default?
Q3IMAP differs from POP3 in that:
Q4FTP uses port 21 for:
Q5HTTP is described as 'stateless' because:
Section B — Short Answer [5 marks]
Q6State the default port for POP3.
Mark schemePort 110 [1 mark].
Q7State one security advantage of using HTTPS over HTTP.
Mark schemeData is encrypted (using TLS/SSL) so it cannot be read if intercepted — prevents eavesdropping / man-in-the-middle attacks [1 mark].
Q8State one security concern with using standard (non-secure) FTP.
Mark schemeStandard FTP sends usernames and passwords in plaintext (unencrypted) — an attacker who intercepts the connection can read the credentials [1 mark].
Q9Which protocol is better suited for a user who reads email on both a smartphone and a laptop — POP3 or IMAP? Give a reason.
Mark schemeIMAP [1]; because emails remain on the server and are synchronised across all devices — reading an email on one device marks it as read on all others [1]. [1 mark for either point].
Q10State the protocol and purpose of two connections used by FTP.
Mark schemeControl connection (port 21) for sending commands such as login, list directory, delete [1]; Data connection (port 20) for transferring the actual file data [1]. [1 mark for either correct pairing].