Link failure detection, network recovery, and network reliability in multi-hop wireless networks

In this thesis, we study Wireless Mesh Network (WMN) and Mobile Ad hoc NETwork (MANET), which are two kinds of wireless multi-hop communication networks. WMNs and MANETs are promising technologies that have the ability to provide effective solutions to many applications in the technological, social, military, disaster recovery, and economic fields. Some of these applications are the extension of the cellular network's coverage, broadband internet access, and community and neighborhood networks. The big challenge in these kinds of networks is the frequent link failures, which make them less reliable compared to other kinds of networks. Implementing a fast mechanism to detect link failures, effective and reliable routing protocols and metrics, and a powerful reconfiguration scheme to recover from the link failures greatly enhance the WMNs and MANETs performance, and increase their reliability and availability. Our research has three directions. In the first direction, we study link failure detection approaches and link failure recovery techniques. In this direction, we mathematically analyze Hello based link failure detection approach implemented in routing protocols that use two routes, one as a primary route, and the other one as a backup route that is immediately used upon link failures. The objectives behind the above analysis are to mathematically calculate the packet delivery ratio, and to find how much gain we could achieve by using two routes instead of one. Our results show that the packet delivery is increased by 1.5 times by using two routes instead of one. It also shows that applying two routes is essential to cover high link failure rate values, and the need using two routes instead of one is more urgent in WMNs and MANETs with higher link failure rate values, i.e. less reliable networks. In addition to that, we propose a novel framework that dynamically assigns the values of Hello based link failure detection scheme parameters based on the communication types and the QoS requirements. Besides that, we propose a novel protocol to enhance the Hello based link failure detection scheme performance. In the second direction, we study the reliable routing protocols and metrics. This thesis proposes a novel adaptive routing protocol to increase the network connectivity and reliability, while minimizing the hop count, reducing the network nodes' spatial distribution and memory, and simplifying the routing process. The network reliability and connectivity are investigated in the last direction. Based in our study, the only ways to provide reliable and stable communications, virtually decrease the packet loss to zero, and to support multimedia communications in MANETs and WMNs are by using multi-route instead of one, and letting the routing protocols select the most stable routes among the available routes. The network node density specifies the probability that a route exists between any randomly chosen source and destination pair. Thus, to ensure the existence of two routes between any source and destination pairs, the node density must be above a certain threshold. In this thesis, we propose a mathematical model to find the above threshold. Our results show that the probability to have two routes exponentially increases with the number of nodes until it reaches the saturation region where the increase of the number of nodes has negligible improvements in terms of network availability. In addition to that, we study the effects of nodes mobility on the network connectivity. Our work is evaluated by MATLAB