This paper details a layered hierarchical switching software structure with standardized logical interfaces. We also evaluated a pilot project to develop a subscriber switching system which implements ISDN call processing as well as POTS based on this concept. The layered interfaces, named S1 and S2, as well as the software structure are based on a concurrent object-oriented design approach in order to improve program maintainability and extendibility of building-block switching systems based on distributed processing. Our approach focuses on quick service provisioning, reducing the total cost and separately developing each software layer. Therefore, we created a pilot project to test our assumptions, and we compared the results with those of existing switching systems. We also discuss the applicability of this technology to the development of switching software.