Resource-on-demand schemes in 802.11 WLANs with non-zero start-up times

Increasing the density of access points is one of the most effective mechanisms to cope with the growing traffic demand in wireless networks. To prevent energy wastage at low loads, a resource-on-demand (RoD) scheme is required to opportunistically (de)activate access points as network traffic varies. While previous publications have analytically modeled these schemes in the past, they have assumed that resources are immediately available when activated, an assumption that leads to inaccurate results and might result in inappropriate configurations of the RoD scheme. In this paper, we analyze a general RoD scenario with N access points and non-zero start-up times. We first present an exact analytical model that accurately predicts performance but has a high computational complexity, and then derive a simplified analysis that sacrifices some accuracy in exchange for a much lower computational cost. To illustrate the practicality of this model, we present the design of a simple configuration algorithm for RoD. Simulation results confirm the validity of the analyses, and the effectiveness of the configuration algorithm

Modeling client arrivals at access points in wireless campus-wide networks

Our goal is to model the arrival of wireless clients at the access points (APs) in a production 802.11 infrastructure. Such models are critical for benchmarks, simulation studies, design of capacity planning and resource allocation, and the administration and support of wireless infrastructures. Our contributions include a novel methodology for modeling the arrival processes of clients at APs and the use of a powerful visualization tool for finding detailed interior features and quantile plots with simulation envelope for goodness-of-fit test. Time-varying Poisson processes can model well the arrival processes of clients at APs. We validate these results by modeling the visit arrivals at different time intervals and APs. Furthermore, we propose a clustering of the APs based on their visit arrival and functionality of the area in which these APs are located.Link_to_subscribed_fulltex

A Simulation-based Methodology for the Assessment of Server-based Security Architectures for Mobile Ad Hoc Networks (MANETs)

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonA Mobile Ad hoc Network (MANET) is typically a set of wireless mobile nodes enabled to communicate dynamically in a multi-hop manner without any pre-existing network infrastructure. MANETs have several unique characteristics in contrast to other typical networks, such as dynamic topology, intermittent connectivity, limited resources, and lack of physical security. Securing MANETs is a critical issue as these are vulnerable to many different attacks and failures and have no clear line of defence. To develop effective security services in MANETs, it is important to consider an appropriate trust infrastructure which is tailored to a given MANET and associated application. However, most of the proposed trust infrastructures do not to take the MANET application context into account. This may result in overly secure MANETs that incur an increase in performance and communication overheads due to possible unnecessary security measures. Designing and evaluating trust infrastructures for MANETs is very challenging. This stems from several pivotal overlapping aspects such as MANET constraints, application settings and performance. Also, there is a lack of practical approaches for assessing security in MANETs that take into account most of these aspects. Based on this, this thesis provides a methodological approach which consists of well-structured stages that allows the exploration of possible security alternatives and evaluates these alternatives against dimensions to selecting the best option. These dimensions include the operational level, security strength, performance, MANET contexts along with main security components in a form of a multidimensional security conceptual framework. The methodology describes interdependencies among these dimensions, focusing specifically on the service operational level in the network. To explore these different possibilities, the Server-based Security Architectures for MANETs (SSAM) simulation model has been created in the OMNeT++ simulation language. The thesis describes the conceptualisation, implementation, verification and validation of SSAM, as well as experimentation approaches that use SSAM to support the methodology of this thesis. In addition, three different real cases scenarios (academic, emergency and military domains) are incorporated in this study to substantiate the feasibility of the proposed methodology. The outcome of this approach provides MANET developers with a strategy along with guidelines of how to consider the appropriate security infrastructure that satisfies the settings and requirements of given MANET context