What mechanisms does the Transport Layer use to check for errors in data transmission?

• A. Checksums and acknowledgments.
• B. IP addresses and port numbers.
• C. ARP and RARP.
• D. Flow control and congestion control.

Answer: (A)

The transport layer achieves error detection and reliable delivery mainly through a checksum mechanism and the use of acknowledgments. A checksum is calculated over the segment's header and payload before sending, and the receiver recomputes it to verify data integrity. If the checksum matches, the data is accepted as intact; if it doesn’t, the segment is discarded, signaling corruption.

Acknowledgments then confirm receipt of data. After a segment arrives correctly, the receiver sends back an acknowledgment to the sender. If an acknowledgment isn’t received in time, the sender retransmits the data. This pairing of error detection (checksum) with delivery confirmation (acknowledgments) underpins reliable transmission and error recovery in the transport layer.

The other options describe functions that aren’t primarily about error checking: IP addresses and port numbers identify the endpoints and the session; ARP and RARP map between IP addresses and hardware addresses; flow control and congestion control manage data rate and network load rather than detect or correct data errors.