TCP/IP is a communication protocol used to connect different hosts in the Internet. It contains four layers, namely the network interface layer, Internet layer, transport layer, and application layer. Which of the following protocols works under the transport layer of TCP/IP?

• A. UDP
• B. HTTP
• C. FTP
• D. SNMP

Answer: (A)

At the transport layer, you have protocols that move data between hosts with end-to-end delivery. UDP fits here because it is a transport-layer protocol that provides a simple, connectionless datagram service with minimal overhead and no guarantees about delivery, order, or duplication. This makes it fast and suitable for time-sensitive tasks where speed matters more than reliability.

The other options are tied to the application layer: HTTP and FTP are application-layer protocols that typically rely on TCP at the transport layer to ensure reliable, ordered delivery. SNMP is also an application-layer protocol, though it often uses UDP as its transport in practice. So among the choices, UDP is the one that operates at the transport layer.