The traditional web is request-response. Real-time apps require a persistent, two-way connection where the server can 'push' data to the client at any time.
SignalR is an abstraction that handles three main transports:
- **WebSockets:** The gold standard. A true, full-duplex persistent connection.
- **Server-Sent Events (SSE):** A one-way push from server to client. Good for notifications.
- **Long Polling:** The legacy fallback. The client opens a request, and the server holds it open until it has data to send.
The beauty of SignalR is that you don't have to choose. SignalR automatically negotiates the best available transport. If the browser or proxy doesn't support WebSockets, it silently falls back to SSE or Long Polling. Your C# code remains exactly the same.
Q: "Why not just use raw WebSockets?"
Architect Answer: "Because raw WebSockets are hard. You have to handle reconnections, heartbeats, grouping, and transport fallbacks manually. SignalR gives you all of this for free, along with a high-level **Hub** abstraction that makes code much more readable and maintainable. Don't reinvent the wheel; use the Ferrari."