The internet's reliability hinges on protocols like TCP and UDP. TCP (Transmission Control Protocol) ensures data arrives intact and in order using a three-way handshake, making it ideal for email, file transfers, and web browsing. Its characteristics include guaranteed delivery, flow control, and error detection, functioning like a tracked courier service.

UDP (User Datagram Protocol) prioritizes speed over reliability. It's connectionless, sending packets without a handshake, which introduces lower latency but no guarantees. This makes UDP perfect for real-time applications like video calls, live streaming, and online gaming where a lost packet is preferable to a delay.

These protocols operate at the transport layer, while HTTP is an application layer protocol that runs on top of TCP. HTTP defines the structure of web requests and responses, but it relies on TCP to handle the underlying delivery. Understanding this stack is key to building efficient, modern applications.