USER DATAGRAM PROTOCOL

What UDP Does

UDP's only real task is to take data from higher-layer protocols and place it in UDP messages, which are then passed down to the Internet Protocol for transmission. The basic steps for transmission using UDP are:

   1. Higher-Layer Data Transfer: An application sends a message to the UDP software.

   2. UDP Message Encapsulation: The higher-layer message is encapsulated into the Data field of a UDP message. The headers of the UDP message are filled in, including the Source Port of the application that sent the data to UDP, and the Destination Port of the intended recipient. The checksum value may also be calculated.

   3. Transfer Message To IP: The UDP message is passed to IP for transmission.

And that's about it. Of course, on reception at the destination device this short procedure is reversed.

What UDP Does Not

In fact, UDP is so simple, that its operation is very often described in terms of what it does not do, instead of what it does. As a transport protocol, some of the most important things UDP does not do include the following:

    * UDP does not establish connections before sending data. It just packages it and… off it goes.

    * UDP does not provide acknowledgments to show that data was received.

    * UDP does not provide any guarantees that its messages will arrive.

    * UDP does not detect lost messages and retransmit them.

    * UDP does not ensure that data is received in the same order that they were sent.

    * UDP does not provide any mechanism to manage the flow of data between devices, or handle congestion.