Data communications – error detection fundamentals In data link communications, what is the term for the error-detecting code field that is inserted into each frame/block before transmission?

Introduction / Context:
Error detection is a core concept in computer networks and serial links. At the data link layer, frames carry not only payload but also a special field designed to detect whether bits were corrupted in transit. Knowing the precise term for this field helps learners distinguish between general concepts (checksums) and the standardized field name used in data link protocols such as Ethernet and HDLC.

Given Data / Assumptions:

• The question asks for the specific name of the error-detecting code field inserted into a transmitted block/frame.
• We are discussing data link layer framing, not higher-layer application checksums.
• Common implementations include CRC-based protection.

Concept / Approach:
Most link-layer protocols append a dedicated field called the Frame Check Sequence (FCS). An FCS typically contains a cyclic redundancy check (CRC) value computed over the header and payload. The receiver recomputes the CRC and compares it with the FCS to detect errors. While the word “checksum” is a broad class of error checks, the standardized field name in link-layer frames is FCS.

Step-by-Step Solution:
Identify the OSI layer: data link (framing and physical delivery).Recognize the standardized field name used in frames: Frame Check Sequence.Understand that FCS often stores a CRC value for robust error detection.Select “Frame check sequence” as the precise answer.

Verification / Alternative check:
Ethernet frames end with a 4-byte FCS. HDLC frames also include FCS. Textbooks and standards consistently use the term FCS for this field.

Why Other Options Are Wrong:
Checksum: generic term; not the specific standardized field name used in link frames.Flow control: regulates data rate; not an error-detection field.Error detecting code (generic): describes the concept, but the formal field name in frames is FCS.

Common Pitfalls:

• Confusing checksums (generic) with the link-layer FCS (specific).
• Assuming FCS always uses the same polynomial; CRC parameters vary by protocol.
• Thinking FCS corrects errors; it only detects them.

Final Answer:
Frame check sequence