What is the internet?
The internet is a global network of networks connected by cables, routers and satellites. It carries data using agreed rules called protocols.
Packets
Data is split into small packets that travel independently and are reassembled at the destination. This lets many people share the same connections and lets data find alternate routes.
The TCP/IP model
| Layer | Job | Examples |
|---|---|---|
| Application | What apps use | HTTP, HTTPS, DNS, SMTP |
| Transport | Reliable delivery between apps | TCP, UDP |
| Internet | Addressing and routing | IP |
| Link | Sending over the physical medium | Ethernet, Wi-Fi |
The OSI model is a more detailed seven-layer version often used in teaching.
TCP vs UDP
- TCP checks that all data arrives in order. It is used for web pages and email.
- UDP is faster with no guarantee. It is used for live video and games.
What happens when you open a website
- Your browser asks a DNS server to convert the name to an IP address.
- It opens a TCP connection to that address.
- For HTTPS, it sets up TLS encryption.
- It sends an HTTP request.
- The server replies with the page and other files.
- The browser renders them.
HTTP basics
GET /index.html HTTP/1.1
Host: example.com
HTTP/1.1 200 OK
Content-Type: text/htmlCommon status codes: 200 OK, 301 redirect, 404 not found, 500 server error.
Security basics
- HTTPS encrypts traffic between the browser and the server.
- Firewalls filter traffic.
- Use strong passwords, updates and two-factor authentication.
Client and server
A client (browser or app) asks for something. A server provides it. Most of the internet works this way.
Next steps
Continue with the Technical Support and Full Stack Development courses to apply these ideas.
Practice
Use the ping and traceroute (or tracert) commands on a website and note how many hops your data takes.