When a faster delivery mechanism is needed and D. When applications do not need to guarantee delivery of the data.
UDP and TCP are both protocols that are used to send bits of data (packets) to the internet. However, if you use UDP, the bits of data are sent directly to the recipient and the protocol would not wait for any confirmation that the data has been received by the recipient before sending the next batch of data on the queue.
This protocol makes the process of data transfer faster because it continuously sends data without any receipt confirmation. However, if the recipient was not able to receive the UDP packet, the data transferred will be incomplete and it may cause the transfer to fail.