Search-based Stress Testing of Wireless Network Protocol Stacks

Abstract—The operation of wireless network protocol stacks is heavily dependent on the actual deployment of the system and especially on the corresponding network topology, e. g., due to channel contention. The nature of wireless communication does not allow for a-priori determination of network topology; network-defining metrics such as neighbor density and routing span may drastically differ for various deployments. Therefore, it is a difficult problem to foresee and consider the large number of possible topologies that a system may run on during protocol stack development. We propose to use an automated approach for searching topologies for which a protocol stack exhibits particularly poor quantitative performance. We formulate stress testing of protocol stacks on specific topologies as a multi-objective optimization problem and use an evolutionary algorithm for finding a set of small topologies that particularly stress the protocol stack of a wireless network. For searching the topology space, we present novel problem-specific variation operators and show their improvements on search performance in case studies. We showcase our results on stress testing using two protocol stacks for wireless sensor networks

Modeling and analysis of influence power for information security decisions

Users of computing systems and devices frequently make decisions related to information security, e. g., when choosing a password, deciding whether to log into an unfamiliar wireless network. Employers or other stakeholders may have a preference for certain outcomes, without being able to or having a desire to enforce a particular decision. In such situations, systems may build in design nudges to influence the decision making, e. g., by highlighting the employer’s preferred solution. In this paper we model influencing information security to identify which approaches to influencing are most effective and how they can be optimized. To do so, we extend traditional multi-criteria decision analysis models with modifiable criteria, to represent the available approaches an influencer has for influencing the choice of the decision maker. The notion of influence power is introduced to characterize the extent to which an influencer can influence decision makers. We illustrate our approach using data from a controlled experiment on techniques to influence which public wireless network users select. This allows us to calculate influence power and identify which design nudges exercise the most influence over user decisions

Quality-of-service provisioning for dynamic heterogeneous wireless sensor networks

A Wireless Sensor Network (WSN) consists of a large collection of spatially dis- tributed autonomous devices with sensors to monitor physical or environmental conditions, such as air-pollution, temperature and traffic flow. By cooperatively processing and communicating information to central locations, appropriate ac- tions can be performed in response. WSNs perform a large variety of applications, such as the monitoring of elderly persons or conditions in a greenhouse. To correctly and efficiently perform a task, the behaviour of the WSN should be such that sufficient Quality-of-Service (QoS) is provided. QoS is defined by constraints and objectives on network quality metrics, such as a maximum end- to-end packet loss or minimum network lifetime. After defining the application we want the WSN to perform, many steps are involved in designing the WSN such that sufficient QoS is provided. First, a (heterogeneous) set of sensor nodes and protocols need to be selected. Furthermore, a suitable deployment has to be found and the network should be configured for its first use. This configuration involves setting all controllable parameters that influence its behaviour, such as selecting the neighbouring node(s) to communicate to and setting the transmission power of its radio, to ensure that the WSN provides the required QoS. Configuring the network is a complex task as the number of parameters and their possible values are large and trade-offs between multiple quality metrics exist. High transmission power may result in a low packet loss to a neighbouring node, but also in a high power consumption and low lifetime. Heterogeneity in the network causes the impact of parameters to be different between nodes, requiring parameters of nodes to be set individually. Moreover, a static configuration is typically not sufficient to make the most efficient trade-off between the quality metrics at all times in a dynamic environment. Run-time mechanisms are needed to maintain the required level of QoS under changing circumstances, such as changing external interference, mobility of nodes or fluctuating traffic load. This thesis deals with run-time reconfiguration of dynamic heterogeneous wire- less sensor networks to maintain a required QoS, given a deployed network with selected communication protocols and their controllable parameters. The main contribution of this thesis is an efficient QoS provisioning strategy. It consists of three parts: a re-active reconfiguration method, a generic distributed service to estimate network metrics and a pro-active reconfiguration method. In the re-active method, nodes collaboratively respond to discrepancies be- tween the current and required QoS. Nodes use feedback control which, at a given speed, adapts parameters of the node to continuously reduce any error between the locally estimated network QoS and QoS requirements. A dynamic predictive model is used and updated at run-time, to predict how different parameter adap- tations influence the QoS. Setting the speed of adaptation allows us to influence the trade-off between responsiveness and overhead of the approach, and to tune it to the characteristics of the application scenario. Simulations and experiments with an actual deployment show the successful integration in practical scenar- ios. Compared to existing configuration strategies, we are able to extend network lifetime significantly, while maintaining required packet delivery ratios. To solve the non-trivial problem of efficiently estimating network quality met- rics, we introduce a generic distributed service to distributively compute various network metrics. This service takes into account the possible presence of links with asymmetric quality that may vary over time, by repeated forwarding of informa- tion over multiple hops combined with explicit information validity management. The generic service is instantiated from the definition of a recursive local update function that converges to a fixed point representing the desired metric. We show the convergence and stability of various instantiations. Parameters can be set in accordance with the characteristics of the deployment and influence the trade-off between accuracy and overhead. Simulations and experiments show a significant increase in estimation accuracy, and efficiency of a protocol using the estimates, compared to today’s current approaches. This service is integrated in various protocol stacks providing different kinds of network metric estimates. The pro-active reconfiguration method reconfigures in response to predefined run-time detectable events that may cause the network QoS to change signifi- cantly. While the re-active method is generally applicable and independent of the application scenario, the, complementary, pro-active method exploits any a-priori knowledge of the application scenario to adapt more efficiently. A simple example is that as soon as a person with a body sensor node starts walking we know that several aspects, including the network topology, will change. To avoid degradation of network QoS, we pro-actively adapt parameters, in this case, for instance, the frequency of updating the set of neighbouring nodes, as soon as we observe that a person starts to walk. At design time, different modes of operation are selected to be distinguished at run-time. Analysis techniques, such as simulations, are used to determine a suitable configuration for each of these modes. At run time, the approach ensures that nodes can detect the mode in which they should operate. We describe the integration of the pro-active method for two practical monitoring applications. Simulations and experiments show the feasibility of an implementa- tion on resource constrained nodes. The pro-active reconfiguration allows for an efficient QoS provisioning in combination with the re-active approach

Energy-Efficiency and Reliability Trade-Off in Wireless Sensor Networks

U ovoj disertaciji je kvantitativno određen odnosa energetske efikasnosti i pouzdanosti u bežičnim senzorskim mrežama na fizičkom sloju i sloju kontrole pristupa medijumu. Pronađene su optimalne vrednosti ovog odnosa u smislu višeciljne optimizacije sa Pareto pristupom, bez preferenci.In this dissertation we quantify energy-efficiency and reliability trade-off in wireless sensor networks at physical and medium access control layers. We find the trade-off optimal solutions in the sense of multi-objective Pareto optimality, without preferences

Configuring heterogeneous wireless sensor networks under quality-of-service constraints

Ph.DNUS-TU/E JOINT PH.D. PROGRAMM

Quality-of-service trade-off analysis for wireless sensor networks

10.1016/j.peva.2008.10.007Performance Evaluation663-5191-208PEEV