ow three times: trans atob (1) : from_ready_input_v76frame trans atob (1) : decision_lose_the_frame(Yes') trans time (12.0) trans dlca!dlc (1) : timeout_t320 trans dlca!dlc (1) : from_waitua_input_t320 82 Validation of Communications Systems with SDL retry1 inst_1_dlca.dispatch inst_1_atob PROCESS/ PROCESS/ v76test/dlca/ v76test/datalink/ dispatch(1) inst_1_dlca.dlc atob(1) I_estabreq( 0) PROCESS/ v76test/ dlca/dlc(1) 'n320cnt= 0' v76frame( sabme : (.0.) ) t320(12.0) v76frame( sabme : (.0.) ) 'n320cnt = 1' t320(12.0) v76frame( sabme : (.0.) ) 'n320cnt = 2' t320 (12.0) v76frame( sabme : (.0.) ) 'n320cnt = 3' t320 (12.0) dicstopped( 0) Figure 4.45 MSC generated by the Simulator showing three SABME retransmissions In the generated MSC, represented in Figure 4.45, you see that the number of retransmission of SABME is correct, but the Simulator indicates37: exception state, Unexpected signal dlcstopped in dlca!dispatch. It means that the signal dlcstopped transmitted by DLC goes into the input queue of process dispatch in block dlca, but unfortunately, in the current state of dispatch, the input of signal dlcstopped is not specified. K. Save the Simulator scenario leading to the bug: in the Simulator, select File > Scenario > Save As, enter retry1 and press save. L. To save the current MSC into the file retryl.msc, type in the Simulator: msc retry1 Do not exit from the Simulator. 4.3.3.2 Analyze the bug To understand the bug, you will search in which state process dispatch (in block dlca) was when process DLC transmitted to it the signal dlcstopped. 37 If you do not see this error, in the Simulator select Edit > Configuration and check the box Trap unexpected signals. Interactive Simulation 83 A. Return to the previous simulation step by pressing the undo Simulator button. In the Simulator, select the transition 38 trans dlca!dlc(1): from_waitua_input_t320 as shown in Figure 4.46, the Editor displays in bold the corresponding input (T320). In the ELSE branch, you see the output of DLCstopped, which caused the problem.