Hang Up Command (Net Bios, 12h)

        This command is used to close or terminate a session. It may be
        issued by either the CALLer or LISTENer. The LSN field contains
        the session number of the session to be closed.

        If any RECEIVE commands for the session are outstanding on the
        machine issuing the HANG UP, they are completed with RETCODE =
        0Ah (session closed). If SEND commands are outstanding, the HANG
        UP completion will be delayed until the SEND has completed.

        If the remote end has any RECEIVE or SEND commands in progress
        when HANG UP is started, they will be terminated with RETCODE =
        0Ah. If no remote RECEIVEs or SENDs are terminated with session
        closed, and if RECEIVE ANY commands are outstanding at the
        remote, one and only one of the RECEIVE ANYs will be terminated
        with the session closed error. If no commands are outstanding at
        the remote machine when the HANG UP occurs, then the next session
        command issued by the remote will be terminated RETCODE set to
        either 08h (invalid session) or 0Ah (session closed).