Abstract. This paper deals with a study and a mathematical model of concurrent Points of Control and Observation (PCOs) realized in Testing and Test Control Notation version 3 (TTCN-3). We study test scenarios that are gaining importance as TTCN-3 is emerging as a notation suitable for conducting load tests too. We investigate communication between parallel test components (PTCs) and analyze race conditions between the queues underlying the implemented PCOs. This way, we build an analytic model to investigate behavior of PCOs under stress conditions and to assess possible latencies messages in a TTCN-3 based load test system might suffer. We present a discrete-time Quasi Birth-Death process to predict performance indices of test components and we propose to use the results to avoid indefinite postponement in the communication of PTCs. Also, we aim to use the model for calculating traffic intensity limits under which it is feasible to use TTCN-3 for load testing. Furthermore, we present the output of the model together with an example load test scenario that is vulnerable to that types of latencies.

In our work, we investigate efficient usage of TTCN-3 based test components in the emerging field of distributed performance testing of communicating systems. TTCN-3 is a high level formal specification language used for the specification of Abstract Test Suites (ATSs) suitable for various testing purposes mainly in telecommunication systems testing. A TTCN-3 based test system may consist of several distributed Parallel Test Components (PTCs) and can be executed utilizing diverse hardware platforms. Our aim is to aid development of load tests by establishing a framework, while collecting best practices at the same time, that can be used to execute tests over mixed hardware resources efficiently. We, mainly focus on automated and dynamic deployment of load test components implemented purely in TTCN-3. Also, the deployment method takes test system load into account by monitoring the participating workstations' behavior on-line. A potential test method is shown that can be used for testing server applications using low-cost or even legacy hardware as the platform for distributed test components. A basic scenario involving SMTP (Simple Mail Transfer Protocol) service testing is presented as an example.

This paper deals with the examination and mathematical modeling of rule-based systems and list topologies applied in software architectures as well as in hardware solutions. In our investigation we focus on telecommunication applications utilizing list topologies. We introduce Quasi Birth-Death processes as the mathematical formalism behind our models. Besides, we extend the simple model of list topologies with respect to the input and output interfaces of the implementation. Furthermore, we present our model on the example of Access Control Lists applied in IP routers and we show results that can be derived from the model. I. INTRODUCTIONIn practice, during the examination of telecommunication or software systems that operate using sequential lists as data structures, and search through these lists by means of various search methods, we faced a significant proposition. Namely, that it might be enough to use simple averaging and to operate with mean values in case we want to optimize the behavior of these systems [17]. But, in case we also want to derive performance indices more precisely the arrival intensity of the traffic needs to be taken into consideration. When the examined system is loaded, queuing appears at the system's interfaces and that has a serious impact on the system's performance. Our aim is to develop a mathematical model that is capable of describing and calculating performance indices more precisely with the system's interfaces included in the investigation.Although, systems previously using sequential lists are replaced in some cases with other structures, e.g. hashes, balanced tree structures, etc., sequential lists are still in operation (maybe by applying a few tricks) in several application areas, e.g. databases, alternative behavior in software architectures, and firewall rules. Namely, these applications operate with lists, sequentially searching through them step-by-step. The replacement of these data structures might solve a few bottlenecks if they can be applied, but we also want to model and investigate existing systems and their performance.Recently, there have been several approaches to automate performance evaluation of software architectures. Most of them start from a software specification that can be given in various formal description languages [8], [9], [10], [11]. In most cases a mathematical formalism is targeted also, as a basis for prediction of various performance indices. Our aim is to develop models that can be easily adopted by setting their

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