In recent years, the networks of low-power devices have gained popularity. Typically these devices are wireless and interact to form large networks such as the Machine to Machine (M2M) networks, Internet of Things (IoT), Wearable Computing, and Wireless Sensor Networks. The collaboration among these devices is a key to achieving the full potential of these networks. A major problem in this field is to guarantee robust communication between elements while keeping the whole network energy efficient. In this paper, we introduce an extended and improved emergent broadcast slot (EBS) scheme, which facilitates collaboration for robust communication and is energy efficient. In the EBS, nodes communication unit remains in sleeping mode and are awake just to communicate. The EBS scheme is fully decentralized, that is, nodes coordinate their wake-up window in partially overlapped manner within each duty-cycle to avoid message collisions. We show the theoretical convergence behavior of the scheme, which is confirmed through real test-bed experimentation.
Both distributed coordination and local synchronization are used to increase stability and facilitate broadcast message transfer @cite_45 @cite_32 @cite_4 . Examples of such schemes include gradient-based @cite_37 and bio-inspired algorithms @cite_5 . Typically bio-inspired algorithms have higher overheads than gradient-based algorithms @cite_41 @cite_42 @cite_0 . However, Gradient-based schemes can be ridged and unable to cope with the dynamism such as node failures @cite_13 . On the other hand, the emergent nature of firefly-based synchronization can cope with failure. Additionally, when a failure happens in another part of the network firefly-based synchronization does not affect the local cluster.
@cite_37 @cite_4 @cite_41 @cite_42 @cite_32 @cite_0 @cite_45 @cite_5 @cite_13
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Accurately synchronized clocks are crucial for many applications in sensor networks. Existing time synchronization algorithms provide on average good synchronization between arbitrary nodes, however, as we show in this paper, close-by nodes in a network may be synchronized poorly. We propose the Gradient Time Synchronization Protocol (GTSP) which is designed to provide accurately synchronized clocks between neighbors. GTSP works in a completely decentralized fashion: Every node periodically broadcasts its time information. Synchronization messages received from direct neighbors are used to calibrate the logical clock. The algorithm requires neither a tree topology nor a reference node, which makes it robust against link and node failures. The protocol is implemented on the Mica2 platform using TinyOS. We present an evaluation of GTSP on a 20-node testbed setup and simulations on larger network topologies. Industrial wireless sensor network (IWSN) is a key enabling technology for the Internet-of-things (IoT). IWSN acts as one of the fundamental elements of the IoT infrastructure to bridge the physical sensors and actuators in field and backbone systems in the Internet. For deterministic performances, all mainstream IWSN standards utilize the slotted media access control (MAC) where the communication is allocated based on the superframe that comprises a number of slots in either contention-based access or contention-free access modes. In this paper, the planning of the superframe structure of the slotted MAC is investigated by two means: 1) a mathematical model of the MAC access latency based on the queue theory; and 2) an easy-to-use software tool based on packet-level simulation. The mathematical model gives an overall estimation of the average MAC access latency of the whole network. The software tool gives the exact latency of each packet and then can derive the optimal superframe structure of the network. The two means are validated correspondingly. With the methods proposed in this paper, IWSN designers can minimize the MAC access latency while satisfying the requirements at different generating rates of packet, number of nodes in the network, and packet buffer length of each node. People have always tried to understand natural phenomena. In computer science natural phenomena are mostly used as a source of inspiration for solving various problems in distributed systems such as optimization, clustering, and data processing. In this paper we will give an overview of research in field of computer science where fireflies in nature are used as role models for time synchronization. We will compare two models of oscillators that explain firefly synchronization along with other phenomena of synchrony in nature (e.g., synchronization of pacemaker cells of the heart and synchronization of neuron networks of the circadian pacemaker). Afterwards, we will present Mirollo and Strogatz's pulse coupled oscillator model together with its limitations. As discussed by the authors of the model, this model lacks of explanation what happens when oscillators are nonidentical. It also does not support mobile and faulty oscillators. Finally, it does not take into consideration that in communication among oscillators there are communication delays. Since these limitations prevent Mirollo and Strogatz's model to be used in real-world environments (such as Machine-to-Machine systems), we will sum up related work in which scholars investigated how to modify the model in order for it to be applicable in distributed systems. However, one has to bear in mind that there are usually large differences between mathematical models in theory and their implementation in practice. Therefore, we give an overview of both mathematical models and mechanisms in distributed systems that were designed after them. Distributed optimization algorithms are highly attractive for solving big data problems. In particular, many machine learning problems can be formulated as the global consensus optimization problem, which can then be solved in a distributed manner by the alternating direction method of multipliers (ADMM) algorithm. However, this suffers from the straggler problem as its updates have to be synchronized. In this paper, we propose an asynchronous ADMM algorithm by using two conditions to control the asynchrony: partial barrier and bounded delay. The proposed algorithm has a simple structure and good convergence guarantees (its convergence rate can be reduced to that of its synchronous counterpart). Experiments on different distributed ADMM applications show that asynchrony reduces the time on network waiting, and achieves faster convergence than its synchronous counterpart in terms of the wall clock time. Fraglets represent an execution model for communication protocols that resembles the chemical reactions in living organisms. The strong connection between their way of transforming and reacting and formal rewriting systems makes a fraglet program amenable to automatic verification. Grounded on past work, this paper investigates feasibility of adopting fraglets as model for specifying security protocols and analysing their properties. In particular, we give concrete sample analyses over a secure RFID protocol, showing evolution of the protocol run as chemical dynamics and simulating an adversary trying to circumvent the intended steps. The results of our analysis confirm the effectiveness of the cryptofraglets framework for the model and analysis of security properties and eventually show its potential to identify and uncover protocol flaws. Traditionally, synchronization barriers ensure that no cooperating process advances beyond a specified point until all processes have reached that point. In heterogeneous large-scale distributed computing environments, with unreliable network links and machines that may become overloaded and unresponsive, traditional barrier semantics are too strict to be effective for a range of emerging applications. In this paper, we explore several relaxations, and introduce a partial barrier, a synchronization primitive designed to enhance liveness in loosely coupled networked systems. Partial barriers are robust to variable network conditions; rather than attempting to hide the asynchrony inherent to wide-area settings, they enable appropriate application-level responses. We evaluate the improved performance of partial barriers by integrating them into three publicly available distributed applications running across PlanetLab. Further, we show how partial barriers simplify a re-implementation of MapReduce that targets wide-area environments. Decentralized synchronization requires cooperation among network participants so that all nodes agree on a common reference timing. What happens if one node does not follow local synchronization rules and randomly transmits? This paper studies the resilience of two classes of decentralized slot synchronization against random disturbances, and quantifies the impact of the random behavior. It is shown that the coupling strength is a key factor for resilience, and that the synchronization approach based on the theory of coupled oscillators generally behaves better and is more robust than the approach that updates clocks based on the average neighboring timings.