User Datagram Format (UDP) is simpler, faster and cheaper than TCP. UDP is connectionless and unreliable which means that it does not establish a virtual circuit like TCP, nor does it demand an acknowledge. It merely sends out the message. UDP headers are all 8 bytes, while TCP headers can be 20-60 bytes long. Like TCP, UDP provides delivery of segments using IP. Below is a diagram of the UDP header:

A description of each of the header components and their size in bits follows:

 UDP is used for things like FINGER and other programs which prioritize speed over reliability, and whose data is not worth the overhead that establishing a TCP connection demands. UDP is neither intelligent enough to compensate for congestion and receiver's speed, nor is it complex enough to care. There is no guarantee that the segments will arrive in order, or at all. It's also possible, if a long enough delay causes a re-send, to receive duplicate segments.

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