To reduce transmission errors, a check figure (checksum/CRC) is computed and appended to the frame/segment. Which endpoint actually computes this check value before sending?

Introduction / Context:
Error detection in data communication relies on adding redundancy to outbound data so the receiver can verify integrity. Common techniques include parity, checksums, and Cyclic Redundancy Check (CRC). Understanding which side computes and appends the check value clarifies how frames and segments are protected in flight.

Given Data / Assumptions:

• Sender and receiver share the same error-detection algorithm.
• The channel can introduce random bit errors, bursts, or other corruption.
• The receiver can recompute the check to validate correctness.

Concept / Approach:
The transmitting endpoint computes the check figure over the payload (and sometimes header fields), then appends it to the outgoing unit (frame/segment). The receiver recomputes the same function over the received data and compares its locally computed value to the received check field. A mismatch indicates corruption and triggers a discard and, depending on layer, a retransmission.

Step-by-Step Solution:

Verification / Alternative check:
Inspect protocol specs: Ethernet adds a 32-bit FCS generated by the transmitter; TCP/UDP include a checksum set by the sender; PPP/HDLC attach a CRC at transmission time. Receivers recompute and verify but do not originate the transmitted check figure.

Why Other Options Are Wrong:

• Receiving computer: it verifies, not appends the original transmitted check.
• Both compute and append: only the sender appends; the receiver merely recomputes for comparison.
• Start/stop bit generator: pertains to asynchronous serial framing, not error-detection value creation.
• None: incorrect because the transmitter is responsible.

Common Pitfalls:
Assuming “both” because the receiver also computes a value; the receiver’s computation is for verification only and is not attached to the transmitted data.

Final Answer:
Transmitting computer