Which statement correctly contrasts UDP and TCP regarding reliability and ordering?

• A. UDP is generally unreliable and does not guarantee in-order delivery; TCP provides reliability and in-order delivery.
• B. UDP guarantees delivery; TCP does not.
• C. Both guarantee delivery in order.
• D. UDP is connection-oriented with a handshake.

Answer: (A)

Reliability and ordering are the key ideas here. UDP is a lightweight, connectionless protocol that sends datagrams without establishing a connection and without guaranteeing delivery or order. Packets can be lost, arrive out of order, or even be duplicated, and there’s no built‑in mechanism to recover lost data.

TCP, in contrast, creates a reliable channel. It uses a handshake to set up a connection, numbers the data, acks received segments, and retransmits any that are lost, ensuring data arrives intact and in the exact order it was sent. It also includes flow control and congestion control to manage the data pace.

That’s why the statement describing UDP as generally unreliable and not guaranteeing in-order delivery, with TCP providing reliability and in-order delivery, is the best fit.

The other options don’t align with how these protocols actually work: UDP does not guarantee delivery; TCP does guarantee delivery; both protocols do not both guarantee in-order delivery; and UDP is not connection-oriented and does not use a handshake.