tures of the simulator to understand it. 6.2 CASE STUDY WITH TAU SDL SUITE In Tau SDL Suite, random simulation mode is available in the Validator, not in the Simulator. 6.2.1 Random simulation without observers You will run the random simulation on the V.76 SDL model to discover errors automatically. 6.2.1.1 Run the random simulation A. If you added an observer process to the model as specified in Chapter 5, go back to the version without observer process: in the Organizer, select V76test, choose Edit > Connect, select To an existing file, press the folder-shaped icon and connect to the file v76test.ssy. Also remove block obs if it remains in the Organizer (but do not delete its file). B. In the Organizer, press the save button, select the SDL system V76test and do Generate > Make. C. In the SDL Make window, select Microsoft Validation or Borland Validation, and press Full Make. D. In the Organizer, press the Validate button to start the Validator. E. In the Validator, press the Navigator button. Validation of Communications Systems with SDL: The Art of SDL Simulation and Reachability Analysis. Laurent Doldi © 2003 John Wiley & Sons, Ltd ISBN: 0-470-85286-0 168 Validation of Communications Systems with SDL F. In the Validator command line, enter: Random-Down 500 The Validator performs a random simulation (limited to 500 transitions), and answers (you may get a different number): No down node after 31 steps If you look at the Navigator, as shown in Figure 6.1, you see why the simulation stopped SO early: Warning: implicit signal consumption of V76frame etc. Navigator Up 1: Transition CONTINUE Pld : AtoB:1 State : ready* Input : V76frame Sender <<Block DLCa>> dispatch:1 Parameter(s) XIDcmd 0 No down node Warning: Implicit signal consumption of signal V76frame Sender: AtoB:1 Receiver: <<Block DLCb>> dispatch:1 Figure 6.1 After 31 random simulation steps If you did not get the same error, repeat the sequence Top, Random-Down 500. This error means that when signal v76frame has been transmitted to process dispatch in b