Which states are typical in the EPD Pilot protocol state machine?

• A. CONN_INIT, CONNECTED, TRANSFER, ERROR, and CLOSED.
• B. INIT, READY, SENDING, DONE.
• C. LISTEN, ACCEPT, RUN, TERMINATE
• D. START, MIDDLE, END

Answer: (A)

Understanding a protocol’s state machine means seeing how a session moves through distinct phases from start to finish. In the EPD Pilot design, a session begins with CONN_INIT, moves to CONNECTED once the setup succeeds, uses TRANSFER for the actual data exchange, can enter ERROR if something goes wrong, and finally ends in CLOSED when the session terminates. This sequence provides clear boundaries for when data can be sent, when faults are handled, and when resources are released. The explicit ERROR state is important because it separates fault handling from normal transfer and termination, giving a controlled path to recover or fail safely. The CLOSED state ensures a clean shutdown with all resources freed. Other option sets don’t fit as well: they either omit essential phases or mix in states from patterns that don’t reflect a per-session lifecycle, such as server-socket styles (LISTEN, ACCEPT) or overly coarse stages (RUN, TERMINATE, START, END) that don’t capture initialization, ongoing transfer, or error recovery.