Which layer provides error detection in Ethernet using CRC?

• A. Physical Layer
• B. Data Link Layer
• C. Network Layer
• D. Transport Layer

Answer: (B)

Error detection with CRC in Ethernet is a function of the Data Link Layer, specifically the MAC sublayer. The frame ends with a Frame Check Sequence (FCS) that contains a CRC value. The sender computes the CRC over the entire frame and puts the result in the FCS; the receiver recalculates the CRC on the received frame and compares it to the FCS. If they match, the frame is considered error-free and delivered to upper layers; if not, it’s discarded. This link-layer check detects errors that occur on the local physical link, not end-to-end. The Physical Layer handles signaling and transmission, the Network Layer handles addressing/routing, and the Transport Layer provides end-to-end reliability with its own mechanisms.