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	English	French
	The checksum of the UDP segment is computed over :
	a pseudo header :rfc:`2460` containing the source address, the destination address, the packet length encoded as a 32 bits number and a 32 bits bit field containing the three most significant bytes set to 0 and the low order byte set to 17
	the entire UDP segment, including its header
	Several types of applications rely on UDP. As a rule of thumb, UDP is used for applications where delay must be minimized or losses can be recovered by the application itself. A first class of the UDP-based applications are applications where the client sends a short request and expects a quick and short answer. The :term:`DNS` is an example of a UDP application that is often used in the wide area. However, in local area networks, many distributed systems rely on Remote Procedure Call (:term:`RPC`) that is often used on top of UDP. In Unix environments, the Network File System (:term:`NFS`) is built on top of RPC and runs frequently on top of UDP. A second class of UDP-based applications are the interactive computer games that need to frequently exchange small messages, such as the player's location or their recent actions. Many of these games use UDP to minimize the delay and can recover from losses. A third class of applications are multimedia applications such as interactive Voice over IP or interactive Video over IP. These interactive applications expect a delay shorter than about 200 milliseconds between the sender and the receiver and can recover from losses directly inside the application.
	Footnotes
	This limitation is due to the fact that the network layer cannot transport packets that are larger than 64 KBytes. As UDP does not include any segmentation/reassembly mechanism, it cannot split a SDU before sending it. The UDP header consumes 8 bytes and the IPv6 header 60. With IPv4, the IPv4 header only consumes 20 bytes and thus the maximum UDP payload size is 65507 bytes.
	A discussion of the ephemeral port ranges used by different TCP/UDP implementations may be found in http://www.ncftp.com/ncftpd/doc/misc/ephemeral_ports.html
	The complete list of allocated port numbers is maintained by IANA_ . It may be downloaded from http://www.iana.org/assignments/port-numbers