What HDLC field is equivalent to the Preamble and SFD fields in an Ethernet Frame?

The HDLC field that is equivalent to the Preamble and Start Frame Delimiter (SFD) fields in an Ethernet frame is the Flag. In HDLC (High-Level Data Link Control), the Flag field is used to signify the beginning and end of a frame. It is represented by the binary sequence 01111110.

This field plays a crucial role in framing, similar to how the Preamble and SFD function in Ethernet. In Ethernet, the Preamble provides a synchronization pattern used for synchronizing the receiver's clock, and the SFD indicates the start of the actual data frame. When a device receives data, it uses these fields to delineate frames, ensuring it can accurately determine where a frame starts and ends.

The other fields in HDLC, such as Control, Address, and Frame Check Sequence, serve different purposes. The Control field is for managing the transmission (like flow control), the Address field identifies the sender and receiver, and the Frame Check Sequence is used for error detection. None of these fields fulfill the same function as the Flag in defining the boundaries of the frame.