les and marketing activity to promote and sell new services, administration activity to control the company general working and other nontechnical processes that are fundamental for a good carrier working. In order to model this complex set of activities, the model developed i [28,29] is based on an activity graph, which correlate various activities in terms of cause and effect. In particular, each activity is connected with other activities with oriented branches, tagged with a probability. This is the probability that if the carrier is carrying on the activity at the beginning of the branch, the activity at the end of the branch also will be needed. A very simple example is given in Figure 8.28 where the graph relative to the process of repairing a failed card in an equipment is shown in detail. In Figure 8.29 a small part of the graph of Figure 8.28 is isolated to show how every element of the graph is tagged with a record containing the main element that are needed to evaluate the impact of the consid- ered step on the cost of the overall activity represented by the graph. The considered example regards a spot process of the reactive type: this means that the process happens at random instants as a reaction to a causing event, in this case the indi- viduation of a failed card in an equipment. All spot events have a trigger; if the event is of the reaction type the trigger is an external event, if the event is a direct action (e.g., the planned substitution of a working but obsolete equipment) the trigger is the arrival of the time at which the action was planned. Telecommunication Networks Critical alarm spare available Field intervention and there is another spare Equip. local test Card change local test or no more spares Verify Activate trigger Activate trigger Error for equipment for equipment functional report agent change change Standard SW maintenance Activater trigger Verify local test SW intervention agent FIGURE 8.28 Activity graph relative to the process of repairing a failed card in an equipment. H