What function does the FCS serve in the Ethernet Trailer?

The Frame Check Sequence (FCS) plays a crucial role in Ethernet communication by providing a method for error detection. It is appended at the end of an Ethernet frame and contains a checksum that is calculated from the frame's contents before transmission. When a receiving device receives the frame, it calculates the checksum again based on the received data and compares it to the FCS value included in the frame. If the two values match, the frame is assumed to be error-free; if they do not match, it indicates that the frame may have been corrupted during transmission, and the frame is typically discarded.

This functionality is essential in maintaining the integrity of data across a network, ensuring that errors introduced by noise, interference, or other issues during transmission are detected promptly. Other options mentioned serve different purposes, such as indicating frame length, identifying the sender, or marking the start and end of frames, but none of these processes relate to error detection as the FCS does.