User Datagram Protocol (UDP) provides the mechanism that lets publishers and subscribers exchange packets of data, called datagrams.
A datagram is an independent, self-contained message sent over the network whose arrival, arrival time, and content are not guaranteed. Although UDP does not guarantee delivery, RAP includes a mechanism to ensure that all messages reach their intended target. Publishers temporarily cache all message packets and subscribers track all messages deliveries. If a message is lost, a subscriber requests a new copy, and the publisher resends the message from the pool of cached messages.