A communications protocol that offers a limited amount of service when messages are exchanged between computers in a network that uses IP. User Datagram Protocol (UDP) is an alternative to TCP. Like TCP, UDP uses the Internet Protocol to actually get a data unit (called a datagram) from one computer to another. Unlike TCP, UDP does not divide a message into packets (datagrams) and reassemble it at the other end. Specifically, UDP does not provide sequencing of the packets that the data arrives in; therefore, the application program that uses UDP must ensure that the entire message has arrived and is in the right order.