User Datagram Protocol is a basic transport protocol that provides a best-effort, connectionless delivery service with minimum overhead. The protocol does not guarantee delivery of packets. There is no checking or retransmission of the data packets. It does provide minimum overhead as it only adds the source and destination port numbers to the header. Since the protocol is unreliable, the application must provide checking, acknowledgments and retransmissions if the data is critical. In many applications, the data is not critical because updates are sent periodically and occasional losses can be tolerated.
UDP sessions may be originated by the local application host or by the network. The DTR signal must be asserted or S211=1 (pretend DTR is always asserted) for the unit to enter into a data communications session. The session is terminated by dropping DTR or resetting the unit.