Compare TCP and UDP in terms of reliability and connection orientation.

• A. TCP is connectionless and unreliable; UDP is connection-oriented and reliable.
• B. TCP is connection-oriented and reliable with in-order delivery; UDP is connectionless, unreliable, and does not guarantee order.
• C. Both provide reliable delivery but only TCP is connection-oriented.
• D. UDP provides in-order delivery; TCP does not.

Answer: (B)

Reliability and whether a connection is established are the key ideas. TCP is connection-oriented: before any data flows, it performs a handshake to set up a connection, and that connection stays open for the duration of the communication. It also provides reliable delivery by acknowledging received data, retransmitting lost segments, and keeping data in order so the receiver assembles the stream exactly as sent.

UDP, on the other hand, is connectionless: there’s no setup phase before sending data. It offers unreliable delivery, meaning there’s no guarantee a datagram will arrive, no automatic retransmission, and no built-in mechanism to ensure packets arrive in the original order. Each datagram is treated independently, which makes UDP faster and lighter-weight for certain applications but less dependable for guaranteed delivery or sequencing.

So the statement that best fits the real behavior is that TCP is connection-oriented and reliable with in-order delivery, while UDP is connectionless, unreliable, and does not guarantee order. The other options contradict these established properties (for example, TCP is not unreliable or connectionless, and UDP does not provide reliable delivery or guaranteed in-order delivery).