UDP

User Datagram Protocol (UDP) runs a distant second place to TCP in terms of the number of applications that use it, but don't let that make you think UDP is not important. UDP is perfect for the types of sessions that don't require the overhead of all that connection- oriented stuff. Probably the best example of an application that uses UDP is the Dynamic Host Configuration Protocol (DHCP). DHCP can't assume there's another computer ready on either side of the session, so each step of a DHCP session just sends the information for that step without any confirmation.

You might also be tempted to think that UDP wouldn't work for any situation in which critical data transfer takes place?untrue! Trivial File Transfer Protocol (TFTP) is one example of a protocol with which you can transfer files from one machine to another. But TFTP, using UDP, doesn't have any data protection, so you would never use TFTP between computers across the Internet. TFTP is popular for moving files between computers on the same LAN, where the chances of losing packets is very small.