UDP — User Datagram Protocol

UDP (User Datagram Protocol) is one of the two main ways a program on one computer sends data to a program on another computer. It works at the transport layer — the part of networking whose job is to hand your data to the network and get it to the right program on the far side. UDP does that job in the simplest, fastest way possible: it just packages your data and fires it off, without setting anything up first and without checking that it arrived.

When two programs on different machines want to exchange data, they need an agreed set of rules for how that data is handed to the network and delivered to the right program — a protocol. There are two dominant transport protocols to choose from: TCP and UDP. TCP (Transmission Control Protocol) is the careful one: it sets up a connection, confirms every piece of data arrived, and puts everything back in order. UDP is the lightweight one: it does none of that extra work, which is exactly why it's faster.

UDP is called connectionless because it never sets up a connection before sending. There's no handshake — no back-and-forth to agree "are you ready? yes, I'm ready." Each chunk of data, called a datagram, is addressed and sent on its own, independently of every other one. The sender doesn't wait for permission and doesn't wait for a reply.

It helps to see where UDP sits in the bigger picture. Networking is organized into layers, each handling one job and passing data to the layer below. UDP lives at the transport layer, just above the layer that moves packets between networks:

UDP delivery is described as unreliable or best-effort. That sounds bad, but it's a precise technical term, not an insult. It means the network will try its best to deliver each datagram, but UDP itself makes no promises: a datagram might be lost along the way, arrive out of order, or even show up twice — and UDP won't detect or fix any of that. If that matters to your app, your app has to handle it.

If UDP can lose data, why use it? Because for some jobs, being fast matters far more than being perfect. Skipping the handshake means there's no delay before the first byte is sent. Skipping acknowledgements and retries means less work and less waiting. For things like a live voice call, a fresh sound sample now is worth more than a perfect copy of a sound from two seconds ago. UDP is the right tool whenever speed and low delay beat guaranteed delivery.