What is the role of TCP in network communication?

• A. To provide reliable, ordered, and error-checked delivery of data.
• B. To provide best-effort, unordered delivery.
• C. To route packets across the internet.
• D. To encrypt data end-to-end.

Answer: (A)

TCP's role is to provide reliable, ordered, and error-checked delivery of data between applications over a network. It does this by establishing a connection, using a three-way handshake, and then transmitting data with sequence numbers so the receiver can reorder any out-of-order segments. Acknowledgments confirm receipt, and any lost or corrupted segments are retransmitted. A checksum in each segment helps detect errors, ensuring integrity. TCP also manages flow control with a sliding window to prevent the sender from overwhelming the receiver, and it uses congestion control to adjust the sending rate based on network conditions.

Other options describe different functions: routing across the internet is handled by IP, not TCP; best-effort unordered delivery is what UDP provides; encryption is handled by other protocols (like TLS/SSL or IPsec), not by TCP itself.