270 A Case Study on Application of CSAN Models on Network Modeling Mohammad Abdollahi Azgomi 1 and Ali Movaghar 2 1 Department of Computer Engineering, Iran University of Science and Technology, Tehran, Iran 2 Department of Computer Engineering, Sharif University of Technology, Tehran, Iran E-mail: azgomi@iust.ac.ir and movaghar@sharif.edu Abstract- Petri nets and their extensions are appropriate formalisms for modeling and analysis of communication systems and networks. A number of timed and stochastic extensions have been introduced for Petri nets. Stochastic activity networks (SANs) is one of these extensions that have been used in several projects for modeling and simulation in this area. We have recently introduced coloured stochastic activity networks (CSANs) as a high-level extension for SAN models. CSAN models can be evaluated by state space analysis techniques or discrete-event simulation. The usage of CSANs for network modeling and simulation has some key benefits over the other existing analytic and simulative techniques. To show these benefits, we have done a case study on modeling and evaluation of a switched LAN using a modeling tool called SANBuilder. In this paper, after an introduction to CSANs, we will present the CSAN models of the case study and the evaluation results. Keywords: Network Modeling, Petri Nets, Coloured Stochastic Activity Networks (CSANs) I. INTRODUCTION Petri nets [16] and their extensions are appropriate formalisms for modeling and analysis communication systems and networks. A number of timed and stochastic extensions have been introduced for Petri nets. Stochastic activity networks (SANs) [14, 15] is one of these extensions, which have been used in several projects for modeling and simulation in this area. In a previous paper [1], we studied the advantages and limitations of the applications of SANs for network modeling. Keeping in mind the requirements for the application of a new high-level extension of SANs in communications systems and networks and to remove the limitations of SANs, we have recently introduced coloured stochastic activity networks (CSANs) as a high- level extension for SAN models [2, 3]. A CSAN model is composed of the five primitives of SANs, including place, input gate, output gate, timed activity and instantaneous activity, plus a new kind of place called coloured place. A coloured place holds a list of tokens of a user-defined token type. The type of the objects being held by a coloured place is defined by a token type. A token type is defined in a way similar to the definition of data types, records or structures in high-level programming languages. Each token type has one or more data fields, which may be an ordinal type or a user-defined type. To each coloured place is associated a selection policy, which defines the order of consuming tokens by corresponding activities. Different kinds of the selection policies are FIFO, LIFO or PRIORITY. This feature of CSANs is useful for modeling in many applications, specially, in communication systems and networks. In addition, for hierarchical modeling, another new element called macro activity is introduced. A macro activity is a CSAN submodel that can be connected to other parts of a hierarchical CSAN (HCSAN) model through fusion places. A macro activity has zero or more input and output fusion places. These fusion places will be bound to the places of the composer HCSAN model. CSAN models can be evaluated by state space analysis techniques or discrete-event simulation. For this purpose, we have developed a modeling tool called SANBuilder [4]. This tool provides an integrated development environment (IDE), which allows the construction, compilation, animation, solution and simulation of SAN-based models in a single user-friendly graphical user interface. The usage of CSAN models and SANBuilder tool for modeling and evaluation of communication systems and networks has some key benefits over the other analytic and simulative techniques. To show these benefits, we have done a case study on modeling and evaluation of a switched LAN using SANBuilder tool. In this paper, after an introduction to CSANs and SANBuilder, we will present the CSAN models of the case study and the evaluation results. The rest of this paper is organized as follows. Section 2 gives a survey on related works. In section 3, a flat and then a hierarchical CSAN model for a switched LAN and the results of their simulation are presented. In section 4, CSAN is compared with other modeling techniques. Finally, some concluding remarks are mentioned in section 5. II. RELATED WORKS Extensions of Petri nets have been used for modeling various kinds and different aspects of communication systems. A collection of papers about applications of Petri nets in communication networks have been assembled in [7] and [8]. In this subsection, we will mention some applications of SANs and coloured Petri nets (CPNs) [9] in this area. In [13], SAN models are used to model and evaluate the interconnection networks for ISDN applications. The main contribution of this work is constructing and evaluating some SAN models for Banyan switches networks. Packet-loss probability and packet time delays are some important measures in the study. In [10], SANs have been used to analyze the distribution of consecutive cell-loss, with respect to both Proceedings of the 5 th International Symposium on COMMUNICATION SYSTEMS, NETWORKS AND DIGITAL SIGNAL PROCESSING (CSNDSP'06), Patras, Greece, July 19-21 (2006)