Network Protocols
A protocol is a set of rules that govern how data is transmitted across a network. Without protocols, devices couldn't communicate — like two people speaking different languages with no translator.
Learning Objectives
- 11.6.2.2 Explain network protocols
Conceptual Anchor
The Diplomatic Protocol Analogy
International diplomacy has protocols: how to greet, who speaks first, what language to use. Network protocols are the same — agreed-upon rules for devices to communicate. TCP/IP is like the universal "language of the internet" that every device speaks.
Rules & Theory
Key Protocols
| Protocol | Full Name | Purpose | Port |
|---|---|---|---|
| TCP | Transmission Control Protocol | Reliable, ordered data delivery (connection-based) | — |
| UDP | User Datagram Protocol | Fast, unreliable delivery (connectionless) | — |
| IP | Internet Protocol | Addressing and routing packets | — |
| HTTP | HyperText Transfer Protocol | Web page requests (not encrypted) | 80 |
| HTTPS | HTTP Secure | Encrypted web page requests | 443 |
| FTP | File Transfer Protocol | Upload/download files | 21 |
| SMTP | Simple Mail Transfer Protocol | Sending email | 25 |
| POP3 | Post Office Protocol v3 | Receiving email (downloads to device) | 110 |
| IMAP | Internet Message Access Protocol | Receiving email (stays on server) | 143 |
| DNS | Domain Name System | Translates domains to IP addresses | 53 |
| DHCP | Dynamic Host Config Protocol | Automatically assigns IP addresses | 67/68 |
TCP vs UDP
| Feature | TCP | UDP |
|---|---|---|
| Connection | Connection-based (handshake) | Connectionless |
| Reliability | Guaranteed delivery, retransmits lost data | No guarantee, no retransmission |
| Order | Data arrives in order | Data may arrive out of order |
| Speed | Slower (overhead from checking) | Faster (minimal overhead) |
| Use case | Web browsing, email, file transfer | Live streaming, gaming, VoIP |
TCP/IP Model (4 Layers)
┌──────────────────────────────────────────────┐
│ Layer 4: APPLICATION │
│ HTTP, HTTPS, FTP, SMTP, DNS, DHCP │
│ (What the user interacts with) │
├──────────────────────────────────────────────┤
│ Layer 3: TRANSPORT │
│ TCP, UDP │
│ (Reliable/unreliable delivery) │
├──────────────────────────────────────────────┤
│ Layer 2: INTERNET │
│ IP, ICMP │
│ (Addressing and routing) │
├──────────────────────────────────────────────┤
│ Layer 1: NETWORK ACCESS │
│ Ethernet, Wi-Fi, ARP │
│ (Physical transmission) │
└──────────────────────────────────────────────┘POP3 vs IMAP
POP3 downloads emails to your device and deletes them from the server — good for one device. IMAP keeps emails on the server and syncs across all devices — the standard for modern email (Gmail, Outlook).
Worked Examples
1 What Happens When You Open a Webpage?
1. You type https://www.example.com in the browser
2. DNS resolves "www.example.com" to IP 93.184.216.34 (DNS protocol, port 53)
3. Browser opens TCP connection to 93.184.216.34:443 (TCP handshake)
4. Browser sends HTTP GET request over HTTPS (HTTPS protocol, port 443)
5. Server sends back HTML, CSS, JS files (HTTP response)
6. Browser renders the page
7. TCP connection closedCommon Pitfalls
HTTP = HTTPS
HTTP transmits data in plain text (anyone can read it). HTTPS encrypts data using TLS/SSL. Always look for the 🔒 padlock in your browser.
Tasks
List 5 network protocols, their full names, and their purposes.
Explain why TCP is used for web browsing but UDP is used for video calls.
Trace the protocols used when you send an email from Gmail to a friend's Yahoo account.
Compare the 4-layer TCP/IP model with a postal delivery system. Map each layer to a real-world equivalent.
Self-Check Quiz
Q1: What protocol is used for sending email?
Q2: What is the main difference between TCP and UDP?
Q3: What port does HTTPS use by default?