Common network protocols
Common Network Protocols
A single network communication typically involves several protocols working together, each handling a different aspect of the exchange. The six protocols you need to know at GCSE level cover three areas: how data is reliably transmitted and addressed (TCP and IP), how web pages are requested and delivered (HTTP and HTTPS), and how email is sent and retrieved (SMTP and IMAP).
Protocols work in layers. IP handles addressing; TCP handles reliable delivery; application protocols (HTTP, SMTP etc.) handle what the data contains.
The Six Protocols in Detail
TCP and IP
These two protocols are so commonly used together that they are often referred to as TCP/IP. They operate at different levels and handle different aspects of data transmission.
IP - Internet Protocol
IP (Internet Protocol) is responsible for addressing and routing. Every device on a network has an IP address - a unique numerical label that identifies it. When data is sent, IP ensures it is addressed correctly so it can be routed from the sender to the correct destination, potentially passing through many different routers and networks along the way. IP treats each packet independently and does not guarantee delivery or ordering.
TCP - Transmission Control Protocol
TCP (Transmission Control Protocol) provides reliable, ordered delivery of data. Before transmission, TCP establishes a connection between sender and receiver. Data is divided into numbered packets. TCP ensures every packet arrives, requests retransmission of any that are lost, and reassembles the packets in the correct order at the destination. It also performs error checking to detect any corruption during transmission. TCP is used wherever complete and accurate delivery matters - such as web pages, files, and emails.
HTTP and HTTPS
HTTP - Hypertext Transfer Protocol
HTTP (Hypertext Transfer Protocol) governs how web browsers request web pages from web servers and how those servers respond. When you type a web address into a browser and press Enter, your browser sends an HTTP request to the server. The server responds with the web page content (HTML, images, CSS, etc.) via HTTP. HTTP defines the format of these request and response messages.
HTTPS - Hypertext Transfer Protocol Secure
HTTPS (Hypertext Transfer Protocol Secure) is an encrypted version of HTTP. It uses SSL/TLS encryption to scramble the data transmitted between the browser and the server, preventing anyone intercepting the communication from reading it. HTTPS is essential for any transaction involving sensitive information - such as entering a password, making a purchase, or submitting personal details. Websites using HTTPS show a padlock icon in the browser's address bar. Any website that does not use HTTPS transmits data in plain text, which can be read by anyone who intercepts it.
SMTP and IMAP
Email involves two separate actions: sending a message from a sender's device to a mail server, and retrieving messages from a server to the recipient's device. Different protocols handle each action.
SMTP - Simple Mail Transfer Protocol
SMTP (Simple Mail Transfer Protocol) is used to send emails. When you press Send in an email client, SMTP transmits your message from your device to your mail server, and then from server to server until it reaches the recipient's mail server, where it waits for collection. SMTP handles outgoing mail only.
IMAP - Internet Message Access Protocol
IMAP (Internet Message Access Protocol) is used to retrieve emails from a server. Unlike older protocols, IMAP keeps the emails stored on the mail server and synchronises them across multiple devices. If you read an email on your phone, it appears as read on your laptop too because both devices are looking at the same copy on the server. This makes IMAP ideal for users who access email from multiple devices.
Quick Reference
| Protocol | Full name | Purpose |
|---|---|---|
| IP | Internet Protocol | Addressing and routing packets across networks |
| TCP | Transmission Control Protocol | Reliable, ordered delivery with error checking |
| HTTP | Hypertext Transfer Protocol | Requesting and delivering web pages |
| HTTPS | Hypertext Transfer Protocol Secure | Encrypted web communication (secure version of HTTP) |
| SMTP | Simple Mail Transfer Protocol | Sending emails from device to server and between servers |
| IMAP | Internet Message Access Protocol | Retrieving emails from a server, with multi-device sync |
Key Takeaways
- IP handles addressing (giving each device a unique address) and routing packets to the correct destination.
- TCP ensures reliable, ordered delivery - splitting data into numbered packets, checking for errors, and reassembling them correctly.
- HTTP governs web page requests and responses; HTTPS is an encrypted, secure version essential for passwords, payments, and personal data.
- SMTP sends emails; IMAP retrieves them from a server and synchronises across multiple devices.