Which protocol is used when guaranteed delivery of each packet is not necessary, using a best-effort delivery mechanism?

• A. UDP
• B. FTP
• C. SSH
• D. TCP

Answer: (A)

Best-effort versus reliable delivery at the transport layer. UDP is the protocol that fits best here because it is connectionless and does not provide guarantees about delivery, order, or error recovery. It simply sends datagrams without establishing a session or performing retransmissions, which makes it fast and lightweight—ideal when occasional packet loss is acceptable, such as in streaming or real-time communications.

In contrast, the other options rely on TCP, which provides reliable, ordered delivery with acknowledgments and retransmission. That means data is guaranteed to arrive correctly, which is not what the question describes. FTP and SSH use TCP under the hood, so they ensure delivery rather than offering best-effort service.