signals. In practice, the simulation is simpler when reasonable environment is on, because there are generally fewer transitions to select in the list. But in certain models, some behaviors can only be simulated when reasonable environment is off (for example, here you cannot send any L_EstabReq to the model before starting the 4 process instances). 106 Validation of Communications Systems with SDL F:ADONNEES\TRANSMETAivreSimul\models0GW76\v76 F:ADONNEESITRANSMETAlivreSimul\models0GW76\v76 File Edit View Execu:e Tools Help File Edit View Execute Tools Help About selection: About selection: Stop if Filter Stop if Filter step = 1 Watch Print trans dicaldispatch start Watch Print trans dicaldispatch start START START NEXTSTATE ready NEXTSTATE ready Traces: Traces: Defaults Defaults Firable Transitions: Firable Transitions: Save Restore Restore atot(1): start atob(1) start btoa(1): start btoa(1) start SDL tracking SDL tracking dicaldispatch : from_ready_input_l_datareq with _datareq(0 diobidiopatch otart Start MSC dicaldispatch from_ready_input_I_datareq with datareq(1 Start MSC Watch dicaldispatch from_ready_input_l_estabreq with _estabreq Watch dicaldispatch from_ready_input__estabreq with _estabreq MSC-driven: dicaldispatch : from_ready_input__setparmreq with _setpare MSC-driven: Activate dicaldispatch from_ready_priority_input_|_releasereq with L Activate dicbidispatch start Redo: Redo: Now 0 Now 0 Verify. Verify. Figure 4.65 Reasonable environment off (a) and on (b) If loose time progression is off, the Simulator will not allow any time progression while the simulation is not 'blocked'. We remind you that in the Simulator, the execution duration of the SDL instructions is supposed to be zero. If you simulate the model shown in Figure 4.66, once you have executed the start transition, timer TIMERI is started, and process procl is in state stl. system L_time block b1 process proc1 SET(TIMER1) proc1 TIMER TIMER1:= 15.0; DCL X Integer; Figure 4.66 Example with timer If loose time progression is off, as shown in Figu