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UDP provides a connectionless, unreliable transport service. Connectionless means that a communication session between hosts is not established before exchanging data. UDP is often used for one-to-many communications that use broadcast or multicast IP datagrams. The UDP connectionless datagram delivery service is unreliable because it does not guarantee data packet delivery and no notification is sent if a packet is not delivered. Also, UDP does not guarantee that packets are delivered in the same order in which they were sent.

Because delivery of UDP datagrams is not guaranteed, applications using UDP must supply their own mechanisms for reliability, if needed. Although UDP appears to have some limitations, it is useful in certain situations. For example, Winsock IP multicasting is implemented with UDP datagram type sockets. UDP is very efficient because of low overhead. Microsoft networking uses UDP for logon, browsing, and name resolution. UDP can also be used to carry IP multicast streams for applications such as Microsoft® Windows Media®.

See Also