Which sublayer adds a trailer to frames to detect transmission errors?

• A. LLC sublayer
• B. Physical sublayer
• C. Network sublayer
• D. MAC sublayer

Answer: (D)

The MAC sublayer adds a trailer to frames to detect transmission errors. At the Data Link Layer, the MAC (Media Access Control) processes frame formatting and handles error detection by computing a Frame Check Sequence (a CRC) over the frame and appending it as a trailer. When the frame is received, the MAC recalculates the CRC and compares it to the FCS in the trailer to determine if the frame was corrupted; if it was, the frame is discarded or flagged. The LLC sublayer focuses on logical link control and multiplexing, not on error-detecting trailers. The Network sublayer handles routing and addressing, while the Physical sublayer deals with signaling and bit-level transmission. So the MAC sublayer is the one responsible for adding the error-detecting trailer.