he expected behavior(s). 1 In fact, an SDL model can be simulated even if some parts are not terminated, such as informal tasks, informal decisions or empty processes. Informal means that the text is placed between single quotes. Validation of Communications Systems with SDL: The Art of SDL Simulation and Reachability Analysis. Laurent Doldi © 2003 John Wiley & Sons, Ltd ISBN: 0-470-85286-0 40 Validation of Communications Systems with SDL Note that this kind of simulation does not verify the performances, such as response time, of the SDL model. For that, special libraries or extensions to SDL are provided by the simulators. 4.2 CASE STUDY WITH TAU SDL SUITE The tools and platform used for the exercises are described in Section 1.5. The V.76 SDL model used for this case study is presented in Chapter 3. As opposed to ObjectGeode, the simulation features of Tau SDL Suite are split in two tools: The Simulator: interactive simulation and automatic simulation, with ready-first scheduling. The Validator: interactive, random and exhaustive simulation, with or without3 ready-first scheduling. 4.2.1 Prepare the Simulator 4.2.1.1 Compile the SDL model A. Download from the Internet (see the ftp address in Section 1.5) or create the SDL V.76 model, and launch Tau SDL Suite Organizer: double-click the icon v76.sdt4, or for Unix: type sdt v76.sdt. The window represented in Figure 4.1 appears. Organizer - v76. sdt File Edit View Generate Tools Help rw v76.sun V76_DLC rw v76_dlc.sbt dispatch rw dispatch.spr rw dlc.spr CRCok rw crcok.spd V76test v76test.ssy DLCa : V76_DLC DLCb : V76_DLC dataLink rw datalink.sbk AtoB toPeer BtoA toPeer toPeer rw topeer.spt System V76test Figure 4.1 The Tau SDL Suite Organizer 2 When two transitions are ready, the one that actually became ready first will be executed. 3 When two transitions are ready, the two can be fired, even the last to become ready. The choice between the two transitions is made according to the simulation mode: either by the user (interactive) or according to a random number (