User Datagram Protocol. UDP is a transport-layer protocol used in IP networks. UDP is a connectionless protocol - the communication partners do not establish a connection before transmitting data. UDP does not provide reliable or in-order transmissions. Datagrams can arrive out of order, arrive duplicated, or go missing during transmission. Applications requiring ordered reliable delivery of streams of data should instead use TCP.
UDP is faster than TCP and has advantages for many lightweight or timing-critical network applications. UDP is used for the Domain Name System on the Internet, for streaming media applications like Voice Over IP, and for broadcasting in IP networks.
UDP uses port numbers 1-65535 to identify application end-points. Examples of well-known UDP services and port numbers are DNS (53), TIME (37), and SNMP (161 and 162).