1. A digital communication unit operating in accordance with an Open Systems Interconnection (OSI) 7-layer communication model, including: a single amalgamated state table into which three OSI upper layer state tables have been merged and comprising an array of cells in rows and columns, the cells containing entries each of which consists of a predicate actions and next state information; table row look-up means responsive to message protocol data units (PDU's); table column look up means storing an amalgamated state; entry logic means for processing the entries of a selected one of the array of cells; predicate logic means for processing the predicate of a selected entry; and a variable list containing the variables referred to by predicates and actions; the variable list including a variable which represents a plurality of session layer states associated with a presentation layer service; and the predicates including a set of new predicates which detect a variety of possible combinations of states of the variable which represents the plurality of session layer states associated with the presentation dervice.