 an MSC (or HMSC), the Validator checks that the events occurring during the simulation are identical to the events specified in the MSC. For example, in Figure 5.22, after the output of sA, the output of sB is expected. Unfortunately, the output of sZ occurs and the Validator detects a violation of the MSC test_seq6. Observer MSC Simulation trace MSC test_seq MSC seq_sim proc1 proc1 inst_1 env_0 inst_proc1 env_0 VIOLATION Figure 5.22 MSC violation 5.2.5.2 The MSC symbols used by the Validator During MSC or HMSC loading (either using the textual command Load-MSC or the button Verify MSC), the Validator checks that all the elements used in the MSC exist in the SDL model. For example, in Figure 5.23, the following checks are performed during MSC loading: The entity named dataLink in the MSC retry1 exists in the SDL model HDLC. The signal v76frame in the MSC also exists in the SDL model. The environment instance contains either env_0 or an external channel name (such as chl here). The name dataLink_I located inside the MSC instance is not supposed to match any SDL name. system HDLC ch1 MSC retry1 block [ v76frame ] dataLink env_0 dataLink_1 datalink v76frame (SABME : (.0.)) SIGNAL v76frame(v76_par); Figure 5.23 An MSC (b) consistent with the SDL model HDLC (a) In ObjectGeode, signal sZ would have been ignored because it is not in the observer MSC. To get a violation as in Tau, sZ must be declared as unexpected signal in the MSC simulation properties. 128 Validation of Communications Systems with SDL MSC retry1 process <<block DLCa>> block dispatch process dataLink <<block DLCa>: timer set DLC_1_5 dataLink_1 DLC_1_5 create T320(12.0) signal output timer reset condition v76frame (sabme : (.0.)) signal parameters signal input ready T320 (12.0) global MSC timer timeout reference reinit1 Figure 5.24 The MSC symbols checked dynamically The following MSC symbols, depicted in Figure 5.24, are dynamically checked by the Val- idator during simulation: Signal input and output and their parameter values, Timer set, reset and ti