Sample Exam on Petri Nets

<strong>Sample</strong> <strong>Exam</strong> on Petri Nets
Exercise 1
Let us consider the Petri net in figure 1. We consider a communication system between
a satellite and control station located on the ground. We assume there are two
classes of messages that must be transmitted: (i) messages that contain data related to
scientific experiences and (ii) messages that contain data related to satellite control and
monitoring.
For the first class, a computer program F 1 is in charge of writting and formatting
the message. Then if the channel C 1 is free, the message is sent.
For the second class, two cases can occur. The first case is the transmittion of
regular messages, while the second case is the transmittion of alarm messages. The
regular messages are written and formatted by a computer program called F 2 . They
are sent through channel C 1 when it is free. The alarm messages are formatted by a
program called F 3 and are transmitted through a special channel, called C a .
1. Show that the system can be modeled by the Petri net, given in figure 1, by
linking the processes related to programs F 1 , F 2 and F 3 to places and by linking
the state of the channels C 1 and C a to other places.
2. Analyse the network, using the method of reduction (clearly justify the rules).
Exercise 2
Let us consider the Petri net in figure 2 (it is a simplified piece of the previous one).
1. Write the incidecne matrix C of the this network and compute P-invariance vectors.
Figure 1: Petri Net A.
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Figure 2: Petri Net B.
2. If we assume that this piece is just related to the management of channel C 1 , do
you think this is correctly managed
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