1 SSCOP Protocol Throughput Evaluation – Simulation Based on Estelle Specification Cristian Negulescu, Eugen Borcoci POLITEHNICA University of Bucharest, Electronics and Telecomm. Faculty, Telecomm. Dept., 1-3 Bvd.Iuliu Maniu, Bucharest -6, 77202, Romania E-mail: ncristi@first.elcom.pub.ro eugenbo@first.elcom.pub.ro ABSTRACT The contribution applies the performance evaluation (PE) methodology, based on annotated Estelle specification simulation, to a real protocol - the Service Specific Connection Oriented Protocol (SSCOP) - approved as B-ISDN ATM Adaptation Layer (AAL) protocol standard by ITU- T. The complete Estelle SSCOP specification was written, conforming the ITU-T Reccomendation Q.2110/1994 and validated for the main connection management and data transfer related functions.The PE are performed on the Estelle Development Tool (EDT/XEDT) developed at Institut National des Télécommunications - Evry, France. We mainly studied - the SSCOP throughput,for different parameters of the user and underlying layer and for different protocol configurations. We obtained similar results to those reported in other studies ( but they used simplified analytical models and/or simulation done on separate models). Our PE run on the real protocol and for extended range of environment conditions, using the rich set of predefined functions of XEDT and appropriated observers. Extensive simulation in severe error conditions have revealed some specification errors and even flow control inefficiencies of the SDL protocol definition Q.2110. Therefore the PE simulations can additionally be used as a complement to the validation process by verification automata and can lead to improvement of the protocol definition. Some simple adaptive flow control policies are proposed and experimented by the authors and show an improved throughput and less control packets overhead. The general conclusion is that the methodology accompanied by a poweful tool is valuable for real life systems design since it gives a user a possibility to evaluate performance in the early stage of protocol development. I INTRODUCTION The performance related features of the communication protocols are currently of increasing interest, especially in the context of high speed networks and new application, like real-time and multimedia traffic carried by such networks. This paper continues some previous work devoted to performance evaluation (PE) and parameter tailoring of complex communication protocols by simulation of their Estelle formal specifications. The general objective is to apply and further develop the Estelle - based methodology for complex protocol design with early performance evaluation. While using the same formal specification as written for validation and implementation of the protocol, predictions on the performance figures can be obtained