We develop two algorithms for important problems in mobile ad hoc networks (MANETs). A MANET is a collection of mobile processors (“nodes”) which communicate via message passing over wireless links. Each node can communicate directly with other nodes within a specified transmission radius; other communication is accomplished via message relay. Communication links may go up and down in a MANET (as nodes move toward or away from each other); thus, the MANET can consist of multiple connected components, and connected components can split and merge over time. We first present a deterministic leader election algorithm for asynchronous MANETs along with a correctness proof for it. Our work involves substantial modifications of an existing algorithm and its proof, and we adapt the existing algorithm to the asynchronous environment. Our algorithm’s running time and message complexity compare favorably with existing algorithms for leader election in MANETs. Second, many algorithms for MANETs require or can benefit from knowledge about the size of the network in terms of the number of processors. As such, we present an algorithm to approximately determine the size of a MANET. While the algorithm’s approximations of network size are only rough ones, the algorithm has the important qualities of requiring little communication overhead and being tolerant of link failures.

<p>Structured overlay networks form a major classof peer-to-peer systems, which are touted for their abilitiesto scale, tolerate failures, and self-manage. Any long livedInternet-scale distributed system is destined to facenetwork partitions. Although the problem of network partitionsand mergers is highly related to fault-tolerance andself-management in large-scale systems, it has hardly beenstudied in the context of structured peer-to-peer systems.These systems have mainly been studied under churn (frequentjoins/failures), which as a side effect solves the problemof network partitions, as it is similar to massive nodefailures. Yet, the crucial aspect of network mergers has beenignored. In fact, it has been claimed that ring-based structuredoverlay networks, which constitute the majority of thestructured overlays, are intrinsically ill-suited for mergingrings. In this thesis, we present a number of research papers representing our work on handling network partitions and mergers in structured overlay networks. The contribution of this thesis is threefold. First, we provide a solution for merging ring-based structured overlays. Our solution is tuneable, by a {\em fanout} parameter, to achieve a trade-off between message and time complexity. Second, we provide a network size estimation algorithm for ring-based structured overlays. We believe that an estimate of the current network size can be used for tuning overlay parameters that change according to the network size, for instance the fanout parameter in our merger solution.Third, we extend our work from fixing routing anomalies to achieving data consistency. We argue that decreasing lookup inconsistencies on the routing level aids in achieving data consistency in applications built on top of overlays. We study the frequency of occurence of lookup inconsistencies and discuss solutions to decrease the affect of lookup inconsistencies.</p>

Structured overlay networks form a major classof peer-to-peer systems, which are touted for their abilitiesto scale, tolerate failures, and self-manage. Any long livedInternet-scale distributed system is destined to facenetwork partitions. Although the problem of network partitionsand mergers is highly related to fault-tolerance andself-management in large-scale systems, it has hardly beenstudied in the context of structured peer-to-peer systems.These systems have mainly been studied under churn (frequentjoins/failures), which as a side effect solves the problemof network partitions, as it is similar to massive nodefailures. Yet, the crucial aspect of network mergers has beenignored. In fact, it has been claimed that ring-based structuredoverlay networks, which constitute the majority of thestructured overlays, are intrinsically ill-suited for mergingrings. In this thesis, we present a number of research papers representing our work on handling network partitions and mergers in structured overlay networks. The contribution of this thesis is threefold. First, we provide a solution for merging ring-based structured overlays. Our solution is tuneable, by a {\em fanout} parameter, to achieve a trade-off between message and time complexity. Second, we provide a network size estimation algorithm for ring-based structured overlays. We believe that an estimate of the current network size can be used for tuning overlay parameters that change according to the network size, for instance the fanout parameter in our merger solution.Third, we extend our work from fixing routing anomalies to achieving data consistency. We argue that decreasing lookup inconsistencies on the routing level aids in achieving data consistency in applications built on top of overlays. We study the frequency of occurence of lookup inconsistencies and discuss solutions to decrease the affect of lookup inconsistencies.