ber should be 41. Save the current Simulator scenario into the file testl.scn, using the command: save testl.scn. Do not exit from the Simulator. 4.3.2.4 Generate a black box MSC The MSC generated in Figure 4.42 contained all the model process instances. You will now generate a more abstract "black box" MSC, containing only the blocks (DLCa, dataLink and DLCb), to validate the external behavior of the system: A. In the Simulator, select File > Generate MSC B. In the Generate MSC window, press the Add button under For entities: C. Select blocks datalink, dlca and dlcb (the selection is multiple) and press OK. D. In the Generate MSC window, press Apply and Cancel (do NOT press Save). E. In the Simulator, press on the buttons init and Redo: All. F. Enter the following Simulator command to generate an MSC in the file testl.msc: msc test1 The Editor loads automatically testl.msc. G. In the Editor, double-click on the box testl to display the generated MSC, similar to the one represented in Figure 4.43, edited to add comments. Exit from the Simulator. 4.3.3 Detect a bug in the SDL model 4.3.3.1 Check the number of retransmissions You will check that the retransmission of SABME occurs maximum three times after its first transmission, as specified in Section 3.2.3. A. Prepare the Simulator as indicated in Section 4.3.2.1. B. Execute the 4 start transitions if not already done. 80 Validation of Communications Systems with SDL test1 inst_dlca inst_datalink inst_dlcb BLOCK/ BLOCK/ BLOCK/ v76test v76test/ v76test /dlca datalink /dlcb /* Establishment of DLC number 0: */ lestabreq(0) v76frame( sabme : (.0.) v76frame( sabme : (.0.) __estabind(0) __estabresp v76frame( (ua:(.0.) v76frame(ua:(.) ) _estabconf(0) /* Exchange identification (XID): */ I_setparmreq v76frame( xidcmd 0 ) v76frame( xidcmd : 0 ) I_setparmind I_setparmresp v76frame( xidresp : 0 ) v76frame( xidresp : 0) I_setparmconf /* Transfer of data 86 through DLC number 0: */ I_datareq( 0,86 ) v76frame(i:(.0,86,15. ) v76frame( i : (. 0,86,15 ) I_dataind( 0,86) Release 