What is the last byte of the preamble called?

The last byte of the preamble is known as the Start Frame Delimiter (SFD). This byte plays a critical role in Ethernet frames, signaling the beginning of the actual frame data. The preamble itself, which consists of several bytes preceding the data, serves to allow devices on a network to synchronize and prepare for receiving the incoming frame.

When this SFD byte is detected, it indicates that the following bits are the start of the frame's header and, ultimately, the data that the network devices will process. This is fundamental in helping to ensure that data is correctly segmented during transmission, allowing for effective communication in network environments.

The other choices do not refer to the last byte of the preamble. The End Frame Marker typically relates to signaling the end of a frame, while the Packet Terminator and Frame Check Sequence have different functions altogether, such as detecting errors within the frame rather than delineating frame boundaries. The SFD is unique in its role of marking the transition from the preamble to the data frame.