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

Cross-Layer Resilience Based On Critical Points in MANETs

A fundamental problem in mobile ad hoc and unstructured sensor networks is maintaining connectivity. A network is connected if all nodes have a communication route (typically multi-hop) to each other. Maintaining connectivity is a challenge due to the unstructured nature of the network topology and the frequent occurrence of link and node failures due to interference, mobility, radio channel effects and battery limitations. In order to effectively deploy techniques to improve the resilience of sensor and mobile ad hoc networks against failures or attacks one must be able to identify all the weak points of a network topology. Here we define the weak or critical points of the topology as those links and nodes whose failure results in partitioning of the network. In this dissertation, we propose a set of algorithms to identify the critical points of a network topology. Utilizing these algorithms we study the behavior of critical points and the effect of using only local information in identifying global critical points. Then, we propose both local and global based resilient techniques that can improve the wireless network connectivity around critical points to lessen their importance and improve the network resilience. Next we extend the work to examine the network connectivity for heterogeneous wireless networks that can be result due to factors such as variations in transmission power and signal propagation environments and propose an algorithm to identify the connectivity of the network. We also propose two schemes for constructing additional links to enhance the connectivity of the network and evaluate the network performance of when a random interference factor occurs. Lastly, we implement our resilience techniques to improve the performance