In addition to Recommendations Z.101 to Z.104, the following rules apply to the logic procedures of the interworking specifications. In accordance with the basic concepts of SDL, internal inputs and outputs are used for logic procedures that do not go beyond the functional block involved. In addition, some SPITEs are used as internal inputs to describe the information flow at the interface between the signalling and switching procedures. All other inputs and outputs, including FITEs and BITEs as well as signals, which pass from one functional block to another are considered as being external.