Self-stabilising Priority-Based Multi-Leader Election and Network Partitioning

A common task in situated distributed systems is the self-organising election of leaders. These leaders can be devices or software agents appointed, for instance, to coordinate the activities of other agents or processes. In this work, we focus on the multi-leader election problem in networks of asynchronous message-passing devices, which are a common model in self-organisation approaches like aggregate computing. Specifically, we introduce a novel algorithm for space- and priority-based leader election and compare it with the state of the art. We call the algorithm Bounded Election since it leverages bounding (i.e. minimisation or maximisation) of candidacy messages to drop or promote candidate leaders and ensure stabilisation. The proposed algorithm is formally proven to be self-stabilising, allows for leader prioritisation, and performs on-the-fly network partitioning (namely, as a side effect of the leader election process, the areas regulated by the leaders are also established). Also, we experimentally compare its performance together with the state of the art of leader election in aggregate computing in a variety of synthetic scenarios, showing benefits in terms of convergence time and resilience

Distributed synchronizers in network simulator (Ns) software

Distributed algorithms are designed for systems consisting of many interconnected processors that communicate with one another by exchanging messages through communication links. Distributed algorithms are used on a wide range of applications, from a VLSI chip to LAN, to the Internet. The advantages of distributed systems include information exchange, resource sharing, replication, parallelization, and modularization; NS (Network Simulator) is an object-oriented, discrete event driven network simulator developed at USC/ISI written in C++ and OTCL. NS is primarily useful for simulating local and wide area networks. It produces one or more text-based output files that contain detailed simulation data. The data can be used for simulation analysis or as an input to a graphical simulation display tool, called Network Animator (NAM); There are two approaches to designing distributed algorithms. In synchronous algorithms, the operation of each process is done in a lock-step behavior, whereas in asynchronous algorithms, the processes take steps in an arbitrary order and at arbitrary relative speeds. Synchronous algorithms are easier to write and prove. However, asynchronous algorithms are easier to implement. Thus, an approach to designing distributed algorithms in asynchronous systems is to start with synchronous algorithms, then transform them into corresponding asynchronous versions by passing them through a special algorithm, called synchronizer. This allows one to use asynchronous systems to run the original synchronous algorithms. The synchronizer itself is an asynchronous algorithm; In this research, we experiment with different types of synchronizers. We implement them by considering two applications: leader election and breadth-first search algorithms. The algorithms are implemented on arbitrary networks. We compare the algorithms in terms of communication complexity. We also discuss the suitability of NS as a platform to implement synchronous and asynchronous algorithms

Leader Election in Anonymous Rings: Franklin Goes Probabilistic

We present a probabilistic leader election algorithm for anonymous, bidirectional, asynchronous rings. It is based on an algorithm from Franklin, augmented with random identity selection, hop counters to detect identity clashes, and round numbers modulo 2. As a result, the algorithm is finite-state, so that various model checking techniques can be employed to verify its correctness, that is, eventually a unique leader is elected with probability one. We also sketch a formal correctness proof of the algorithm for rings with arbitrary size

Automated Synthesis of Distributed Self-Stabilizing Protocols

In this paper, we introduce an SMT-based method that automatically synthesizes a distributed self-stabilizing protocol from a given high-level specification and network topology. Unlike existing approaches, where synthesis algorithms require the explicit description of the set of legitimate states, our technique only needs the temporal behavior of the protocol. We extend our approach to synthesize ideal-stabilizing protocols, where every state is legitimate. We also extend our technique to synthesize monotonic-stabilizing protocols, where during recovery, each process can execute an most once one action. Our proposed methods are fully implemented and we report successful synthesis of well-known protocols such as Dijkstra's token ring, a self-stabilizing version of Raymond's mutual exclusion algorithm, ideal-stabilizing leader election and local mutual exclusion, as well as monotonic-stabilizing maximal independent set and distributed Grundy coloring