Before diving into the techniques, let's understand the problem they solve.

In a traditional web request (HTTP), the flow is simple:

1. The client (your browser) sends a request.
2. The server responds with data.
3. The connection closes.

This is fine for loading a webpage. But what if you want the server to tell you something without you asking first? What if new data arrives every second? That's the real-time problem.

The three solutions:

• Polling — Client keeps asking: "Any new data?"
• SSE (Server-Sent Events) — Server pushes updates to the client automatically.
• WebSocket — Client and server talk to each other freely, simultaneously.