UDP

UDP sends each packet (a datagram) on its own: no handshake, no acknowledgements, no resending and no ordering. A lost packet is simply gone, and the app decides whether that matters. Its header is only 8 bytes, against at least 20 for TCP, and there is no connection to keep track of.

That suits real-time traffic, where a late packet is as useless as a lost one. Video calls, online games and live streams run over UDP, and so do most DNS lookups. QUIC, the base of HTTP/3, builds its own reliability on top of it. Some office networks block UDP, which is one reason WebRTC can fall back to TURN relays over TCP or TLS.