For a live game, a voice call or a stream, data arriving late is worse than data not arriving at all. UDP is built around exactly that idea. It adds almost nothing to the raw delivery service underneath it: no handshake, no ordering, no acknowledgements and no retransmission.
What that buys is time. There is no waiting for a lost packet to be resent, and no later data held up behind an earlier packet that has gone astray. Applications built on UDP take on whatever jobs TCP would have done for them, and usually conclude that a missing fragment of audio or a stale position update is simply not worth recovering.
Three things to remember
- UDP has no handshake, no acknowledgements and no retransmission. It sends and moves on.
- Removing loss recovery removes the delay that comes with it, which is what real-time traffic needs.
- Anything UDP does not provide has to be handled by the application, or accepted as lost.
Related explanations
- What Happens When You Hit Send? (Your Download Is Faking It)
- What Happens When You Hit Enter? (It’s Always DNS)
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