User Datagram Protocol (UDP)

Obviously, writing code to deal with reassembling fragmented datagrams would make you think twice about how badly your application needs to communicate over a network. Fortunately, the Internet architects provided a protocol layer that sits on top of the Internet Protocol.

UDP uses the Internet Protocol to send datagrams from a source to a destination. When the datagram arrives at the destination, it hands the complete datagram packet to the client. If the datagram was fragmented along the way, it reassembles the fragments into a complete datagram beforehand.

Like the Internet Protocol it uses, UDP does not guarantee delivery of a datagram. Its purpose is simply to format a datagram with your data, send it via the Internet Protocol to a destination, and at the destination, deliver the complete datagram to a client.

One interesting aspect of the Internet Protocol is that datagrams can be delivered to a destination in a different sequence than the one in which they were sent. For example: your application sends two datagrams to another computer. The first datagram is routed along a longer path than the second datagram, and therefore arrives at the destination after the second datagram has arrived.