One aspect of the invention provides an apparatus for modelling a plurality of switching operations arranged in a plurality of switching stages. The apparatus comprises a respective switch stage component for each switching stage, and each switch stage component comprises a respective addressable switch state indicator for each switching operation associated with the respective switching stage. The values of the switch state indicators in a given switch stage component identify a respective switch state indicator in another switch stage component. The switch stage components are interconnected such that addressing a switch state indicator in one switch stage component causes the respective identified switch state indicator in another switch stage component to be addressed. In the preferred embodiment, each switch stage component comprises a respective Look-Up Table.