Unicast UDP Usage Guidelines for Application Designers

The User Datagram Protocol (UDP) provides a minimal message-passing
transport that has no inherent congestion control mechanisms.
Because congestion control is critical to the stable operation of the
Internet, applications and upper-layer protocols that choose to use
UDP as an Internet transport must employ mechanisms to prevent
congestion collapse and to establish some degree of fairness with
concurrent traffic. This document provides guidelines on the use of
UDP for the designers of unicast applications and upper-layer
protocols. Congestion control guidelines are a primary focus, but
the document also provides guidance on other topics, including
message sizes, reliability, checksums, and middlebox traversal.