 the Simulator can also be used to observe an SDL model with an MSC, using the Organizer command Simulator Test > New Simulator. 114 Validation of Communications Systems with SDL obs_1 inst_dlca Figure 5.4 The observer MSC obs_1 of the MSC to verify: in this case, the Simulator will not explore the states leading to an error (a violation) of the MSC, because the default configuration is error cut (equivalent to prune in Tau). 5.2 CASE STUDY WITH TAU SDL SUITE In Chapter 4, we have used the Tau SDL Suite Simulator. To benefit from automatic observation features, we will now switch to the Tau SDL Suite Validator. Note that the Simulator can also be used to check the SDL model against an MSC. 5.2.1 Simulate with user-defined rules In the Validator, only one user-defined rule can be used at a time. To check several conditions, you can use the operator or to group them in a single rule. 5.2.1.1 Detect DLC establishment We want to detect that a DLC is established. This means, in our V.76 SDL model, that: instance 1 of process DLC in block DLCa is in state connected, and instance 1 of process DLC in block DLCb is in state connected. It seems that the Validator rules do not accept qualifiers such as <<Block DLCa> there are two processes named DLC, one in block DLCa and the other in block DLCb, it is not possible to write a rule to detect that both DLCs are in state connected. An observer process could be used instead. The solution would be to modify the SDL model to have a copy of block V76_DLC on each side: transformation of the block type V76_DLC into a block named V76a, making a copy of it and naming the copy V76b and in each block, renaming the DLC process, respectively, DLC a and DLC_b. Then, the Validator user-defined rule would be: state (DLC_a : 1) =connected and state (DLC_b 1) =connected Rather than performing this model modification, you will use rules concerning process AtoB and BtoA, which do not require the use of qualifiers, as they are unique in the system. Automatic Observation of Simulations 115 5.2.1.2