User datagram protocol

The User Datagram Protocol (UDP) is one of the core Internet protocols. It is a layer 4 protocol (Transport layer of the OSI model) within the Internet protocol suite. It provides a mechanism to identify different endpoints on a single host by means of ports. UDP doesn't have the handshake overhead of TCP to establish connections, and does not have features like flow control and reliability like TCP. UDP deals with single packet delivery, provided by the underlying IP.

As a stateless protocol it is often used in such applications where data must arrive quickly, and data that arrives late is worthless. The benefit of this smaller feature set is quicker data transmittal, and lower total overhead, hence its common usage is for real time applications like videoconferencing, online gaming, voice over IP and other streaming media.

UDP packets (also known as datagrams) contain, in addition to the lower level headers, a UDP header, which consists of a checksum, the packet length, plus source, and destination ports.

In special circumstances, UDP, combined with application-level connection and reliability management, provides one useful advantage over TCP: the ability to hold connections to thousands of users at once, unrestricted by limitations on TCP hard-coded into an operating system's often proprietary kernel.

As with TCP, UDP ports are 16-bit entities, so that a maximum of 65535 different endpoints are possible within a single IP address.