Which transport protocol is best suited for reliable, ordered delivery over an unreliable network?

• A. TCP
• B. UDP
• C. ICMP
• D. SCTP

Answer: (A)

Guaranteeing reliability and maintaining the correct order of data across an unreliable network requires a transport protocol that handles acknowledgments, retransmissions, and sequencing. This is exactly what TCP does. It establishes a connection, assigns sequence numbers to data, and uses acknowledgments to confirm receipt. If a packet is lost or corrupted, TCP retransmits it, and it reorders any out-of-sequence data so the application receives a clean, continuous stream in the correct order. It also employs flow control to prevent the sender from overwhelming the receiver and congestion control to adapt to network conditions.

UDP, by contrast, is a best-effort, connectionless protocol with no guarantees about delivery or ordering, so it isn’t suitable for reliable, ordered delivery. ICMP operates at the network layer and isn’t used for transporting application data. SCTP can provide reliability and ordering as well, but TCP is the standard, widely supported choice for reliable, in-order data transfer over IP networks.