Q.931 call protocol validation and performance assessment, based on LOTOS

This paper reports the validation and performance analysis of a Q.931 signalling software, which was developed in the frame of the project Factory Customer Premises Network (FCPN, Esprit P2198). In FCPN, a top-down stepwise refinement approach was used, supported by the LOTOS formal description technique. This approach was based on a sequence of design steps, where each step consisted of three tasks: production of the target design, assessment of the design, and prototyping or implementation. This paper addresses the second task, i.e. the assessment of the Q.931 protocol specification. The assessment of the functional requirements is based on testing. The main issues involved in the testing task are discussed, and the test suite derived for the Q.931 specification is described. The non-functional requirements are considered using two different approaches. Firstly, the paper reports real performance measures taken in Q.931 protocol prototype implemented with the LOTOS-to-C compiler TOPO. Secondly, it presents an extension of the LOTOS language called LOTOS-TP, which includes simulation oriented features, and discusses its application to the Q.931 specification. The resulting model can be used to simulate the Q.931 protocol and evaluate its performance in various environments