Performance evaluation of buffered multiple-path ATM switch architectures A.A.VEGLIS 1 AND A.S.POMBORTSIS 2 1 Computer Lab Dept. of Journalism & MMC 2 Dept. of Informatics Aristotle Univ. of Thessaloniki 54006 Thessaloniki - Greece. Abstract: The performance analysis of network architectures is a very crucial factor in designing ATM high- speed communications networks. Very often, simulation is the only feasible method because of the nature of the problem and because analytical techniques become too difficult to handle. However simulation can be costly to develop and run. The mathematical analysis approach is preferable but in most cases not applicable. This paper presents an evaluation of buffer Clos network that is based on the analytical simulation method, that has been presented in [6]. The method comprises the probabilistic analysis and the simulation technique with the help of a mathematical software package. The analysis enables us to observe the behavior of various parameters of the network architecture under various traffic conditions. Keywords: performance evaluation, analytical simulation, Clos networks, uniform traffic load. 1. Introduction. Asynchronous Transfer Mode is the high-edge technology employed in an increasing number of WAN production links, because of its high throughput and guaranteed quality of service that is able to provide. Different taxonomies of ATM switches can be found, depending on the parame- ters assumed as a key to classify different struc- tures [4]. Two of the most significant features of these structures are their blocking / nonblocking property and the type of buffers arrangement in the structure. Blocking networks are typically multi- stage structures that support one path between any inlet and outlet. Early ATM switch designs were mostly based on variations of banyan networks [7]. These net- works have simple routing control, modular con- struction and can be pipelined, but do not have the required performance. Clos network is a multi- stage network that consists of three stages. It is widely used in telecommunications, and has been the focus of much research [8]-[11]. This network provides multiple paths between any input - output pair, and thus exhibits superior performance and fault tolerance in comparison with the conventional multistage networks [3, 5]. The performance of the network is a crucial factor in designing an ATM architecture. The methods for performance evaluation of network architectures fall into two categories: measurement techniques and predictive techniques [7]. The later category comprises mathematical analysis and simulation. Measurement methods require real networks to be available for experimentation. Very often, simulation is the only feasible method, because of the nature of the problem and because analytical techniques become too difficult to handle. However simulation can be costly to develop and run. The mathematical analysis approach is preferable, but in most cases not applicable. The method with the lower computational cost and with good accuracy for evaluating interconnection networks is the probabilistic analysis with independence assumption [2, 3, 5]. But this method can only be applied to networks without buffers. This paper presents an evaluation of buffer Clos network that is based on the analytical simulation method that has been presented in [6]. The study enables us to observe the behavior of various parameters of the network under various traffic conditions. The rest of the paper is organized as follows: Section 2 includes a description of a Clos network. In Section 3 we analyze the performance of the Clos network under uniform traffic. The simulation environment is discussed in Section 4. Some numerical results are presented in section 5. Concluding remarks can be found in Section 6. 2. Network description The Clos Network was introduced by Clos in [1]. It is defined by three integer parameters f, n, r, and can