oa (1) : decision_lose_the_frame 'Yes') This prevents the Simulator from losing the frame in block dataLink. L. Press on to start the random simulation: at Step 12 (you may get a different number), the simulation stops (deadlock). M. Press on init KI, press four times on redo (to skip the start) and then on the simulation stops at Step 41, indicating success(test1). It means that this time, the Simulator has selected the correct transitions, simulating the behavior expected by the MSC testl. If you simulate manually with the same Simulator settings (filter etc.), you will see that most of the time there is only one transition to fire; therefore the probability to randomly play Random Simulation 179 the expected scenario is high. If you remove filter error(observation), the success is extremely difficult to obtain randomly. 6.3.4 Details on random simulation 6.3.4.1 Testing the simulator randomness To know exactly the repartition of random choices performed by the Simulator, we have sim- ulated the model shown in Figure 6.8. Each spontaneous transition increments a variable, to count the number of time it is executed by the Simulator. After executing the first transition (start), the Simulator, as expected, proposes five firable transitions, as illustrated in Figure 6.9. Then we remove the traces to speed up the simulation and enter the following command to run 1000 random simulation steps: go until rstep = 1000 system syst1 block block1 process proc1 block1 proc1 n5 Integer:= 0; n1:=n1+1 n2:= n2 + 1 n3:= n3 + 1 n4:= n4 + 1 n5:= n5+1 Figure 6.8 SDL model to test random choices $ F:ADONNEES\TRANSMETAlivreSimul\modelsOGAxxxrand\rand File Edit View Execute Tools Help About selection: step = 1 Stop if Filter trans proc1(1): start Watch Print Traces: Firable Transitions: Defaults proc1(1) : from_st1_input_none_1 proc1(1) from_st1_input_none_2 Save Restore proc1(1) from_st1_input_none_3 proc1(1) from_st1_input_none_4 SDL tracking proc1(1): from_st1_input_none_5 Start MSC 1001/1001 Watch. Now: 0 MSC-driven Figure 6.9 The