When to Use UDP

In brief

When throwing away TCP's guarantees is the right call — DNS, live video, games — and the trade-off that makes UDP fit them.

Objectives

Contrast TCP and UDP guarantees
Pick the right protocol for a job
Explain the on-time-beats-complete idea

TCP guarantees delivery and order, at the cost of the handshake and retransmissions. UDP throws that away: it fires packets and does not care if they arrive. That sounds worse, but for the right job it is exactly right.

	TCP	UDP
Guarantees delivery	Yes	No
Ordered	Yes	No
Overhead	Higher	Minimal
Good for	Web, files, mail	DNS, video calls, games

Note

A dropped frame in a video call is better ignored than re-sent a second too late. That is the whole argument for UDP — sometimes on-time beats complete.

Recap

UDP drops TCP's guarantees for minimal overhead
Use it for DNS, live video and games
Sometimes on-time matters more than complete