UDP - User Datagram Protocol

The User Datagram Protocol is an alternative protocol to TCP, that is used for low-latency and loss tolerating connections. Both, UDP and TCP resides at the 'transport layer' of the TCP/IP protocol suite. They are one of the core protocols of the TCP/IP protocol suite.

There are 2 main functions of the UDP protocol. First, it assigns port number to each process and forwards the incoming packet to that port. Second, UDP protocol checks the ordering of incoming frames, that the complete message arrives intact and in-order.

UDP protocol doesn't send any type of control information along with the IP Datagrams, there by reducing the "size" of the UDP message to a larger extent. 

Working of UDP protocol
UDP is a connectionless protocol as oppose to TCP. This means the receiver don't acknowledge the received frames, so even if the frame get lost during the transmission, sender won't be informed.

Another thing is that, as oppose to TCP, a UDP message don't follow any specific order, the messages that arrives first are the ones to be displayed first. These features of UDP protocol makes it suitable for a limited and specific type of applications like video conferencing, IP telephony, media streaming etc. 

Difference between UDP and TCP
The major difference between TCP and UDP is that, TCP is a connection-oriented protocol i.e, the receiver is acknowledged about the status of the message - received or lost. In case of UDP no such synchronization is maintained, the sender won't be informed of the lost or corrupted frames.