Module Level Communication Protocol Specifications of Applications Software for Distributed Computing Systems

Abstract

While the advantages of distributed computer systems are well established and documented,⁽¹⁾ the technology for developing distributed software is still very immature. A distributed software system consists of a number of distributed processing components (DPCs), which are each executing on a different processing node of the distributed computer system. Each DPC, in turn, consists of a number of functional modules; modules which reside in different DPCs must communicate via message passing. Naturally, the most important aspects of distributed software systems are the communication mechanisms which are required for both message exchange based communication and synchronization. These communication mechanisms are referred to as communication protocols. The ISO Reference Moder defines these communication protocols into seven different layers. The “lowest” layer is called the physical layer and the “highest” layer is called the applications layer. In this paper, we are only concerned with the communication protocols of the applications layer. Specifically, we present guidelines for deriving the applications layer communication protocols for modules which comprise a distributed software system. The techniques which we are presenting are intended for use during the design phase of the software lifecycle, as opposed to the implementation phase. In order to represent (document) the protocols used, we use a communications-based design representation scheme which is based on the Petri net model.⁽³⁾