def AE_5(dul):
    """Association establishment action AE-5.

    From Idle state, on receiving a remote connection attempt, respond and
    start ARTIM. This is the first step in associating a remote AE (requestor)
    to the local AE (acceptor).

    State-event triggers: Sta1 + Evt5

    Parameters
    ----------
    dul : dul.DULServiceProvider
        The DICOM Upper Layer Service instance for the local AE

    Returns
    -------
    str
        ``'Sta2'``, the next state of the state machine
    """
    # Start ARTIM timer
    dul.artim_timer.start()

    return 'Sta2'