In data communications, which summation-based operation is applied to blocks of bits to verify integrity as an error-detecting code at the receiver?

Introduction:
Error detection ensures that corrupted data is identified so that it can be retransmitted or discarded. One of the simplest integrity checks computes a summarized value over a block of bits and sends it with the data. The receiver recomputes the same value and compares the results to detect errors. This question asks for the name of that summation-based mechanism.

Given Data / Assumptions:

• The mechanism operates over a block (e.g., a segment, packet, or frame payload).
• The transmitter computes a numeric summary and appends it.
• The receiver recomputes that summary and compares to the transmitted value.

Concept / Approach:
A checksum is produced by summing (often using 1's complement arithmetic or modular sums) all words in a block and then sending the complement or the final sum as the checksum field. The receiver performs the same summation; a mismatch indicates that one or more bits were altered in transit. While more robust methods like CRCs are widely used at the data link layer, checksums remain common at the transport layer (e.g., UDP/TCP) and in file formats due to their simplicity and speed.

Step-by-Step Solution:

Verification / Alternative check:
In practice, IP, TCP, and UDP include 16-bit checksums. Many firmware images and archive formats also use checksums for basic integrity assurance, confirming the term and its application.

Why Other Options Are Wrong:

• Codec/Coder-decoder: devices or algorithms that convert between analog/digital or compress/decompress; not integrity checks.
• Attenuation: signal power loss over distance; unrelated to integrity verification.
• None of the above: incorrect because “checksum” precisely matches the description.

Common Pitfalls:
Assuming all error detection uses CRCs; forgetting that checksums are still prevalent at higher layers due to speed and ease of implementation.

Final Answer:
Checksum.