Marco Ajmone Marsan, Gianfranco Balbo. A Class of Generalized Stochastic Petri Nets for the Performance Evaluation of Multiprocessor Systems. ACM Transactions on Computer Systems, Vol. 2, No. 2, May 1984, pp. 93-122.
Click http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.90.8002&rep=rep1&type=pdf link to open resource.