The User Datagram Protocol (UDP) is a transport layer protocol defined for use with the IP network layer protocol. It is defined by RFC 768 written by John Postel. It provides a best-effort datagram service to an End System (IP host).
A special class of applications can derive benefit from having partially damaged payloads delivered, rather than discarded, when using paths that include error-prone links. Such applications can tolerate payload corruption and may choose to use the Lightweight User Datagram Protocol (UDP-Lite) [RFC3828] variant of UDP instead of basic UDP.
The header format closely follows that of UDP. UDP-Lite changes the semantics of the UDP "payload length" field to that of a "checksum coverage length" field. Otherwise, UDP-Lite is identical to UDP. Like UDP, UDPLite uses the ports field to identofy the payload of the upper layer protocol that is being used.
The interface of UDP-Lite differs from that of UDP by the addition of a single (socket) option that communicates a checksum coverage length value: at the sender, this specifies the intended checksum coverage, with the remaining unprotected part of the payload called the "error insensitive part".
By default, the UDP-Lite checksum coverage extends across the entire datagram. If required, an application may dynamically modify this length value, e.g., to offer greater protection to some messages. UDP-Lite always verifies that a packet was delivered to the intended destination, i.e., always verifies the header fields. Errors in the insensitive part will not cause a UDP datagram to be discarded by the destination. Applications using UDP-Lite therefore must not make assumptions regarding the correctness of the data received in the insensitive part of the UDP-Lite payload (this may have been changed). The sending application therefore needs to specify a minimum checksum coverage that include all sensitive protocol headers.
[RFC4505] provides guidance on how to use UDP and UDP-Lite.
See also:
Standards Documents:
L. Eggert, G. Fairhurst, Unicast UDP Usage Guidelines for Application Designers, RFC4505
List of Assigned UDP Port Numbers
Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., Ed., and G. Fairhurst, Ed., "The Lightweight User Datagram Protocol (UDP-Lite)", RFC 3828, July 2004.
Renker, G. and G. Fairhurst, "MIB for the UDP-Lite protocol", RFC 5097, January 2008.