Network Protocols - Class Notes

✅ What is a Network Protocol?

A network protocol is a set of rules that allows devices to communicate with each other over a network.

Protocols define:

How data is formatted
How data is sent and received
How errors are handled
How devices identify each other

✅ Why Do We Need Network Protocols?

Without protocols:

Devices would not understand each other
Data could arrive incomplete or corrupted
Networks would be unreliable
Security would be difficult

Protocols make networking possible by ensuring communication is organized, reliable, and compatible.

✅ Real-World Analogy

Think of sending a letter:

Address format → IP Addressing
Postal rules → Protocol rules
Delivery confirmation → Acknowledgments
Secure envelope → Encryption

🌐 Protocol Layers (Simplified Model)

Networks use layers so each protocol has a specific job. Layers make complex networking easier to build and troubleshoot.

1️⃣ Application Layer

User-facing protocols (what apps and browsers use).

HTTP / HTTPS
FTP / SFTP
SMTP
DNS

2️⃣ Transport Layer

Controls how data moves between devices.

TCP (Transmission Control Protocol)

Reliable (checks for errors)
Connection-based
Slower but accurate
Used for web browsing, email

UDP (User Datagram Protocol)

Faster
No guaranteed delivery
Used for streaming, gaming, voice/video calls

3️⃣ Internet Layer

Handles addressing and routing between networks.

IP (Internet Protocol)

Assigns addresses to devices
Routes data across networks

Example IP Address: 192.168.1.1

4️⃣ Network Access Layer

Handles physical transmission (wired/wireless).

Ethernet
Wi-Fi

🌐 Common Network Protocols

🌍 HTTP (HyperText Transfer Protocol)

Used for websites
Not encrypted
Port 80

http://example.com

🔒 HTTPS (Secure HTTP)

Encrypted version of HTTP
Protects data in transit
Port 443

https://example.com

📧 SMTP (Simple Mail Transfer Protocol)

Sends email between servers

📥 POP3 / IMAP

POP3 downloads email to a device
IMAP syncs email across devices

🌐 DNS (Domain Name System)

Translates website names into IP addresses
DNS = Internet “phone book”

google.com → 142.250.x.x

📂 FTP (File Transfer Protocol)

Transfers files between computers
Secure version: SFTP

🔐 SSH (Secure Shell)

Secure remote login
Used by IT and cybersecurity professionals

🌐 Ports (Important Concept)

Protocols use ports like “door numbers” so the right service receives the right data.

Protocol	Common Port
HTTP	80
HTTPS	443
FTP	21
SSH	22
DNS	53

🌐 Packet Basics

Data is broken into small pieces called packets. Packets travel across networks and get reassembled at the destination.

Each packet can include:

Source address
Destination address
Data (payload)
Error-checking info

🌐 Security Considerations

Some protocols are secure by design, while others are not.

✅ More Secure

HTTPS
SSH
SFTP

⚠️ Less Secure

HTTP
FTP
Telnet

Cybersecurity professionals often replace insecure protocols with secure versions (example: FTP → SFTP, HTTP → HTTPS).

🌐 Example: What Happens When You Visit a Website?

You type a website address (like google.com).
DNS converts the name into an IP address.
Your browser uses TCP to establish a connection.
HTTPS encrypts the communication.
The server sends webpage data back to your browser.

🌐 Key Vocabulary

Protocol
Packet
IP Address
Port
Encryption
DNS
TCP
UDP

✅ Summary

Network protocols are rules that allow devices to communicate across networks safely and reliably. Different protocols handle tasks like web browsing, email, file transfer, naming (DNS), and secure communication.