If ATP quantities are insufficient, orders can be promised on the basis of capable-to-promise (CTP) quantities,
indicating the slack capacity remaining after matching available capacity with already committed customer orders.
In case of unforeseen events, like a breakdown of machines, shortage planning comes into play, specifying which (committed) customer orders will not be served in time.
Only simple rules are implemented in standard software so far (Fischer, 2001; Kilger and Schnee-weiss, 2002)