Which of the following uses UDP services?

TFTP, or Trivial File Transfer Protocol, is designed to be a simpler, lightweight alternative to FTP for transferring files. One of the main characteristics of TFTP is that it operates over UDP (User Datagram Protocol) instead of TCP (Transmission Control Protocol). This decision is based on TFTP's intended use case, which typically involves scenarios where quick transfers of files are necessary, and the overhead of a connection-oriented protocol like TCP is not warranted.

Using UDP allows TFTP to deliver data without establishing a connection, enabling it to send packets with less latency. While this means TFTP has some limitations, such as the lack of built-in error checking, it is well-suited for applications like transferring firmware images to devices where speed is a priority, and the overhead of ensuring delivery is either handled at a different level or is acceptable.

In contrast, protocols like HTTP, FTP, and SMTP require reliable connections and error-checking mechanisms, which is why they utilize TCP. TCP's features include connection establishment, reliable delivery, and flow control, making it preferable for tasks that require guaranteed data transmission integrity.