What is the role of checksums in a transport protocol?

• A. Detect corruption
• B. Guarantee delivery
• C. Encrypt payload
• D. Enable multiplexing

Answer: (A)

Checksums at the transport layer exist to detect corruption that can occur as data traverses the network. A checksum value is computed from the segment’s header and payload and sent with the segment. When the receiver gets it, it recalculates the checksum and compares it to the transmitted value. If they don’t match, the receiver knows the data was corrupted in transit and can discard the faulty segment or trigger retransmission, preventing corrupted data from being delivered to the application.

This role is why the option focusing on corruption detection is the best fit. It does not guarantee delivery—reliability comes from additional mechanisms like acknowledgments and retransmission. It also doesn’t encrypt the payload, which would be about confidentiality, nor does it enable multiplexing, which is about distinguishing multiple concurrent streams using port numbers.