At the Data Link layer, which mechanism is typically used to detect transmission errors on a link?

Introduction:
Reliable communication starts with detecting corrupted frames on each hop. The Data Link layer appends error-detection information so that receivers can discard damaged frames and request retransmission at an appropriate layer. This question asks you to identify the standard mechanism used for detection at Layer 2.

Given Data / Assumptions:

• Focus is strictly on error detection at the Data Link layer.
• Common Layer-2 technologies include Ethernet, PPP, HDLC, and others.
• We are not being asked about forward error correction used on some physical links.

Concept / Approach:
Most Data Link protocols use a frame check sequence computed via a Cyclic Redundancy Check (CRC). The transmitter computes the CRC over the frame; the receiver recomputes and compares. A mismatch signals a corrupted frame. Other techniques listed either serve different purposes or are used at different layers.

Step-by-Step Solution:

Verification / Alternative check:
Ethernet uses a 32-bit CRC (FCS). HDLC/PPP use FCS variants (often CRC-16/CRC-32). These are classic examples of Layer-2 error detection in practice.

Why Other Options Are Wrong:

• Bit stuffing: a framing method to avoid flag patterns within data, not error detection.
• Hamming codes: error correction; not the typical Layer-2 detection mechanism.
• Equalization: mitigates channel distortion at the Physical layer.
• None: incorrect because CRCs are standard.

Common Pitfalls:
Confusing framing (bit stuffing) with integrity checks; thinking that any error-related term implies detection at Layer 2.

Final Answer:
Cyclic redundancy codes (CRC/FCS).