User Datagram Protocol

The User Datagram Protocol (UDP) is a core member of the Internet protocol suite, defined in RFC 768. It provides a simple, connectionless communication model that allows applications to send datagrams without establishing a dedicated end‑to‑end connection. Unlike the Transmission Control Protocol (TCP), UDP offers no guarantees for delivery, ordering, or duplicate protection, making it suitable for real‑time applications where low latency is more critical than reliability.

UDP is widely used in services such as Domain Name System (DNS) lookups, Dynamic Host Configuration Protocol (DHCP), Voice over IP (VoIP), online gaming, and live video streaming. Its minimal protocol overhead—just an 8‑byte header—enables efficient, low‑overhead data transfer in networks where packet loss can be tolerated or handled at the application layer.

Features

Connectionless: No handshake is required before data transmission. Each datagram is independent, which reduces setup delay.
Unreliable: No acknowledgments, retransmissions, or sequence numbers. Lost packets are not recovered by the protocol.
No congestion control: UDP does not throttle its sending rate, allowing applications to send at full speed.
Lightweight header: The header consists only of source and destination ports, length, and a checksum.
Broadcast and multicast support: UDP can send datagrams to multiple recipients simultaneously, unlike TCP.

History

UDP was designed by David P. Reed and formally specified in 1980 as RFC 768 by the Internet Engineering Task Force. It was intended to complement TCP by providing a minimal transport service for applications that could tolerate loss or that required low‑overhead messaging. The protocol has remained essentially unchanged since its publication and is standardized as STD 6.

Comparison with TCP

While TCP ensures reliable, ordered delivery with flow control, UDP sacrifices these guarantees for speed and simplicity. Applications that can handle their own reliability (e.g., QUIC) often use UDP to avoid the overhead of TCP’s connection management and congestion algorithms.

Applications

DNS – queries and responses are typically sent over UDP on port 53.
DHCP – uses UDP for broadcast‑based address assignment.
Streaming media – Real‑Time Transport Protocol (RTP) often runs over UDP.
Online gaming – requires low latency; lost packets are preferable to delayed retransmissions.
Trivial File Transfer Protocol (TFTP) – a simple file transfer protocol using UDP.

User Datagram Protocol