UDP
UDP is a lightweight, connectionless transport protocol that sends datagrams with minimal overhead, trading reliability for low latency.
UDP, the User Datagram Protocol, is a minimal transport protocol of the internet. It sends discrete messages, called datagrams, from one host to another with very little overhead and no connection setup.
How It Works
UDP is connectionless. A sender simply transmits a datagram to a destination address and port without a handshake. There are no acknowledgments, no retransmissions, no ordering, and no built-in flow or congestion control. Each datagram is independent and may arrive out of order, be duplicated, or be lost entirely. UDP does add a checksum to detect corruption and ports to direct datagrams to the right application.
Because UDP provides so little, any reliability an application needs must be built on top of it. This is exactly what QUIC, the transport beneath HTTP/3, does, layering its own streams, ordering, and recovery over UDP.
Why It Matters
UDP's lack of guarantees is a feature for latency-sensitive workloads. Live voice and video, online gaming, and real-time telemetry prefer to drop a late packet rather than wait for a retransmission that would arrive too late to use. DNS also uses UDP for fast, single-exchange lookups.
The trade-off is that applications must tolerate or repair loss and disorder themselves. UDP is the right tool when speed matters more than perfect delivery, or when an application wants full control over its own transport behavior, as modern protocols increasingly do.
Related Terms
UDP is the counterpart to TCP, underpins HTTP/3 via QUIC, carries DNS, and is chosen for low latency.