Abstract
This paper describes a method of verifying an SDL specification of a switching system by utilizing the algebraic properties of Petri Nets (PN). In order to verify the SDL specification, it is converted into PN, which have been an excellent tool for modeling an asynchronous and parallel system. SDL is based on a finite state machine (FSM) model and FSM can be easily converted into PN. However, SDL has other functions than FSM such as creation and deletion of a process instance, or realization of a synchronous communication between processes by adding a ‘wait’ state. The SDL specification is converted into PN considering these functions. In this paper, Colored Petri Nets (CPN) are used because they have more powerful modeling ability than conventional Petri Nets. Two kinds of invariants, S-invariant and T-invariant, can be calculated from the incidence matrix of the created Petri Nets which means connections between transitions and places. Then, boundness of the specification is verified by S-invariants, and liveness and deadlock-freeness by T-invariants. It is very difficult to get the invariants from the incidence matrix in CPN, because the elements of the matrix are not integers. However, the proposed method can utilize the invariants got from the incidence matrix of conventional PN, which are created from CPN. Besides, in a case that engineers design the SDL specification incrementally, they can ensure the correctness which the specification had before they add new services to it, by checking the invariants. Finally, the method is successfully applied into design of a PBX prototyping system.
