The User Datagram Protocol (UDP) provides the lowest level of service that can be used conveniently by network application programs. UDP is most often used when applications implement their own networking protocol and thus require little intervention from the TCP/IP software.
In addition to the communication capabilities of IP, UDP adds checksums for the application data and protocol ports to help distinguish among the different processes that are communicating between sending and receiving machines. A checksum detects errors in the transfer of a packet from one machine to another. A protocol port is an abstraction used to distinguish between multiple destinations within a single host.
A datagram is a basic unit of information transferred across a network. UDP does not guarantee that datagrams reach their destination, nor does it ensure that the datagrams are received in the order in which they are sent. Because UDP does not use connections or sessions, it is called a connectionless protocol.
UDP ports are two-byte integers that specify a particular service or program within a host computer. For example, port 13 is generally used by programs that query the date and time maintained by a particular host. A client-server relationship is usually defined in a UDP transaction. The server waits for messages (listens) at a predefined port. When it receives a datagram from a new client, the server knows where to respond because the datagram contained both the sender's IP address and its port number.
Copyright © 2001 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
