For complex software systems, a central design concern is system architecture. The systematic treatment of architectural specification and refinement is a proper basis for an engineering approach to system design. However, conventional Petri nets models do not provide adequate abstractions for architectural specification, because their primary concern is behavior modeling and analysis. As an attempt to address this problem, we present a formal model called NOAM (Net-based and Object-based Architectural Model) for architectural specification and prototyping of real-time distributed systems. Building on the existing contributions from Petri nets, NOAM not only supports precise specification of real-time behavior embodied in a system architecture, but also provides a framework for systematic architectural refinement and exploration. Special focus is placed on using the formal model, and our support environment to prototyping NOAM specifications, and to meet real-time constraints.