A Novel Approach for Survivability of IEEE 802.11 WLAN Against Access Point Failure

In the last decade, wireless networks have become increasingly popular as powerful and cost-effective platforms for mobile communications. Unfortunately, current wireless networks are notoriously prone to a number of problems, such as the loss of link-level connectivity due to user mobility and/or infrastructural failures, which makes it difficult to guarantee their reliability. Today’s users are mostly satisfied with the ability to access wired networks/resources conveniently from mobile stations, even if the access is unreliable. However, as wireless networks become more ubiquitous and start to support more critical applications, users will expect wireless networks to provide the same guarantees of reliability as their wired counterpart are often able to ensure. Research is ongoing to extend the scope of services made available to mobile users to achieve the “anytime, anyplace, any form” communications vision. This vision is to provide voice, data, and multimedia services to users regardless of location, mobility pattern, or type of terminal used for access. In IEEE 802.11 Wireless LAN, if an access-point fails, then, all the mobile stations connected to a wired network via the access-point may lose connectivity. In this thesis work, the problem of enhancing the survivability of IEEE 802.11 WLAN focusing on tolerating Access Point (AP) failures is addressed. In particular, focus on the problem of overcoming these APs failures working with reconfiguration of the remaining APs by changing parameters like the neighboring AP’s MAC address is done. This approach consists of two main phases: Design and Fault Response. In Design phase, we deal with quantifying, placement and setting up of APs according to both area coverage and performance criteria. In Fault Response phase we consider the reconfiguration of the active APs in order to deal with AP fault in the service area

Design and Evaluation of Online Fault Diagnosis Protocols forwireless Networks

Any node in a network, or a component of it may fail and show undesirable behavior due to physical defects, imperfections, or hardware and/or software related glitches. Presence of faulty hosts in the network affects the computational efficiency, and quality of service (QoS). This calls for the development of efficient fault diagnosis protocols to detect and handle faulty hosts. Fault diagnosis protocols designed for wired networks cannot directly be propagated to wireless networks, due to difference in characteristics, and requirements. This thesis work unravels system level fault diagnosis protocols for wireless networks, particularly for Mobile ad hoc Networks (MANETs), and Wireless Sensor Networks (WSNs), considering faults based on their persistence (permanent, intermittent, and transient), and node mobility. Based on the comparisons of outcomes of the same tasks (comparison model ), a distributed diagnosis protocol has been proposed for static topology MANETs, where a node requires to respond to only one test request from its neighbors, that reduces the communication complexity of the diagnosis process. A novel approach to handle more intractable intermittent faults in dynamic topology MANETs is also discussed.Based on the spatial correlation of sensor measurements, a distributed fault diagnosis protocol is developed to classify the nodes to be fault-free, permanently faulty, or intermittently faulty, in WSNs. The nodes affected by transient faults are often considered fault-free, and should not be isolated from the network. Keeping this objective in mind, we have developed a diagnosis algorithm for WSNs to discriminate transient faults from intermittent and permanent faults. After each node finds the status of all 1-hop neighbors (local diagnostic view), these views are disseminated among the fault-free nodes to deduce the fault status of all nodes in the network (global diagnostic view). A spanning tree based dissemination strategy is adopted, instead of conventional flooding, to have less communication complexity. Analytically, the proposed protocols are shown to be correct, and complete. The protocols are implemented using INET-20111118 (for MANETs) and Castalia-3.2 (forWSNs) on OMNeT++ 4.2 platform. The obtained simulation results for accuracy and false alarm rate vouch the feasibility and efficiency of the proposed algorithms over existing landmark protocols

Preface

Elçi, Atilla ( Aksaray, Yazar )Since the beginning of the publication of Subaltern Studies in the early 1980s, new interest has been generated in the study of subalterns in South Asian society. Numerous articles have been written on the subalterns, in historical as well as contemporary contexts. Most of the studies on subalterns are, however, narratives of the socio-political experiences of subalterns and their contribution to society, ignored by the mainstream history; at least the twelve volumes of Subaltern Studies remained centrally concerned with that. On the other hand, critics of subaltern studies challenged the approaches and methodologies of subaltern studies. The question of subaltern reproduction has neither been given appropriate attention in the series of Subaltern Studies, nor has been underlined as the new context of undertaking studies on subalterns. The critics too missed the issue of subaltern reproduction. The issue that is of critical importance to understanding subalterns is their reproduction: why and how does a society produce and reproduce subalterns? How do subalterns negotiate their social and political emancipation? How do they absorb social and political changes? These questions are relevant in historical as well as contemporary contexts. This volume is an attempt to capture some of the processes of the use of ideology, knowledge and power to reproduce subalterns and subalternity in Indian society; to map the dominant trajectories of emancipation and assertion adopted by the subalterns; and to analyse the forces of social and cultural changes including resistance to those changes