This paper presents a method for modeling of communication protocols using G-Nets — an object-based Petri net formalism. Our approach focuses on specification of one entity in one node at one time, with the analysis that allows consideration of other layers and nodes in addition to module analysis. We extend G-Nets by the notion of timers, which aids the construction of protocol software models. Our method prevents some types of potential deadlocks and livelocks from being introduced into the produced net models. We present certain net synthesis rules to prevent some potential design errors by including error cases in the model. Thus, our node (site) interplay modeling includes cases in which a message may arrive corrupted or can be lost entirely before it would get to its destination node. Also, since our models have deadlock-preserving skeletons, the verification of global deadlock non-existence can be performed on the less complex skeleton rather than on the full G-Net model. Our analysis method discovers some deadlocks plus other unacceptable markings, which do not allow restoration of the initial state. Finding potential livelocks or overspecification is also a part of the analysis.
