Contact Synchronization for the Android Platform

Evaluation of contact synchronization algorithms for the Android platform

Wireless sensor and actuator networks (WSAN) have become pervasive and are found in many embedded and intelligent systems. However, the complexity of applications based on WSANs is limited due to the lack of programming tools for this type of networks. In this paper, we show how a concurrent programming language, SystemJ, is used to develop a middleware-free distributed system that consists of a combination of stationary and mobile WSAN nodes. A distributed Ambient Intelligence (AmI) monitoring and control scenario that consists of collaborating stationary and mobile WSAN nodes with high degree of reactivity is presented. The system is designed and implemented using SystemJ to demonstrate the proposed system-level design approach. SystemJ is designed specifically to handle reactive and concurrent behaviors while providing modular and scalable methodology for distributed system composition. In addition, SystemJ removes the need for a middleware and allows system designers to focus on implementing system functionality rather than to deal with the low level programming details.

Location information is the major component in location based applications. This information is used in different safety and service oriented applications to provide users with services according to their Geolocation. There are many approaches to locate mobile nodes in indoor and outdoor environments. In this paper, we are interested in outdoor localization particularly in cellular networks of mobile nodes and presented a localization method based on cell and user location information. Our localization method is based on hello message delay (sending and receiving time) and coordinate information of Base Transceiver Station (BTSs). To validate our method across cellular network, we implemented and simulated our method in two scenarios i.e. maintaining database of base stations in centralize and distributed system. Simulation results show the effectiveness of our approach and its implementation applicability in telecommunication systems.

We discuss two fundamental problems that arise in distributed systems: first, how to determine the order in which various events were executed, and second, how to obtain a consistent view of the system. To address the first problem, we describe different schemes that implement an abstract notion of time and can be used to order events in a distributed system. To address the second problem, we discuss ways to obtain a consistent state of the system possibly satisfying certain desirable property.

At the present time, information systems affect all aspects of our life, due to the technological advance in communications, in particular, the increase of wireless networks, ad-hoc, mobile devices, that provide access to the information. The implementation of secure and high quality distributed systems and applications is highly required. Such systems can be implemented in a small, medium and large scale. For the scaling of a system or application is required to consider the properties and qualities of the distribution, as well as drawbacks. E-Government is one of the most complex and important sectors for the application of technological development in information systems. An important aspect for the development and efficiency of distributed systems is the design paradigm or architectural style. The selection and development of a framework is an essential part for implementing a system architecture, because the framework allows connection between the concepts of architecture and platform. The plan focuses in the exploration and integration of system architecture, desirable properties and development frameworks for distributed system, especially considering the e-government applications.

Data synchronization-long a staple in le systems-is emerging as a signicant communications primitive. In a distributed system, data synchronization resolves di erences among distributed sets of information. In named data networking (NDN), an information-centric communications architecture, data synchronization between multiple nodes is widely used to support basic services, such as public key distribution, le sharing, and route distribution. While existing NDN synchronization schemes are unctional, their implementations rely on log-based representations of information, which creates a limitation on their performance and scalability. This paper presents iSync, a high performance synchronization protocol for NDN. iSync supports efficient data reconciliation by representing the synchronized datasets using a two-level invertible Bloomfilter (IBF) structure. A set-differences can be found by subtracting a remote IBF from a local IBF. The protocol can obtain multiple differences from a single round of data exchange, and does not require prior context in most application scenarios. We evaluated iSync's performance by comparing it to the CCNx synchronization protocol. Experiments show that iSync is about eight times faster across a range of network topologies and sizes, and that it reduces the number of packets sent by about 90%.

In distribution systems, network reconfiguration and capacitor control, generally, are used to reduce real power losses and to improve voltage profiles. Since both capacitor control and network reconfiguration belong to the complicated combinatorial optimization problems, it is hard to combine them efficiently for better optimization results. In this paper, a joint optimization algorithm of combining network reconfiguration and capacitor control is proposed for loss reduction in distribution systems. To achieve high performance and high efficiency of the proposed algorithm, an improved adaptive genetic algorithm (IAGA) is developed to optimize capacitor switching, and a simplified branch exchange algorithm is developed to find the optimal network structure for each genetic instance at each iteration of capacitor optimization algorithm. The solution algorithm has been implemented into a software package and tested on a 119-bus distribution system with very promising results.

Problem diagnosis in large distributed computer systems and networks is a challenging task that requires fast and accurate inferences from huge volumes of data. In this paper, the PMC diagnostic model is considered, based on the diagnostic approach of end-to-end probing technology. A probe is a test transaction whose outcome depends on some of the system's components; diagnosis is performed by selecting appropriate probes and analyzing the results. In the PMC model, every computer can execute a probe to test a dedicated system's components. Furthermore, any test result reported by a faulty probe station is unreliable and the test result reported by fault-free probe station is always correct. The aim of the diagnosis is to locate all faulty components in the system based on collection of the test results. A dual-cube DC(n) is an (n + 1)-regular spanning subgraph of a (2n + 1)-dimensional hypercube. It uses n-dimensional hypercubes as building blocks and returns the main desirable properties of the hypercube so that it is suitable as a topology for distributed systems. In this paper, we first show that the diagnosability of DC(n) is n + 1 and then show that adaptive diagnosis is possible using at most 22n+1 + n tests for a 22n+1-node distributed system modeled by dual-cubes DC(n) in which at most n + 1 processes are faulty. Furthermore, we propose an adaptive diagnostic algorithm for the DC(n) and show that it diagnoses the DC(n) in three testing rounds and at most 22n+1 + O(n3) tests, where each node is scheduled for at most one test in each round.

This paper proposes an extension of the precision time protocol (IEEE 802.1AS) to improve clock synchronization in hybrid networks including both wireless and wire-bound segments. This extension targets systems based on Time Sensitive Networking (TSN) such as industrial applications and vehicular systems. By considering the deterministic delays and the clock drift, the precision of the clock synchronization of the standard 802.1AS scheme can be significantly improved. Furthermore, in order to support dynamic communication environments with mobile nodes, the problem of asymmetric delays in the transmission of the timing packets of the synchronization protocol is also considered. Therefore, a Path Deviation Delay (PDD) filter is introduced to monitor the traffic behavior of timing packets as well as to exclude outlier values which can occur as a result of dynamic and asymmetric scenarios. The paper presents a simulation framework for the proposed protocol to evaluate it with TSN-based systems that support the TSN features (e.g. IEEE 802.1Qci and IEEE 802.1Qbv sub-standards). The simulation results show that the proposed protocol improves the synchronization precision compared with the standard 802.1AS protocol. It shows that the proposed protocol enhances the synchronization precision to less than 1 microsecond. In contrast, the synchronization error increases significantly with the standard protocol in the presence of different asymmetric ratios and in mobile node scenarios.

While dealing with Mobile Distributed systems, we come across some issues like: mobility, low bandwidth of wireless channels and dearth of stable storage on mobile nodes, disconnections, inadequate battery power and high failure rate of mobile nodes. Minimum-process coordinated checkpointing is considered an attractive methodology to introduce fault tolerance in mobile systems transparently. In this paper, we propose a non-blocking coordinated global state compilation algorithm for mobile computing systems, which requires only a minimum number of processes to take permanent recovery points. We reduce the communication complexity as compared to the Cao-Singhal algorithm [4], while keeping the number of useless recovery points unchanged. Finally, the paper presents an optimization technique, which significantly reduces the number of useless recovery points at the cost of minor increase in the communication complexity. In coordinated global state compilation, if a single process fails to take its tentative recovery point; all the recovery point effort is aborted. We try to reduce this effort by taking soft recovery points in the first phase at Mobile Hosts.

Coordinated checkpointing is an effective fault tolerant technique in distributed system as it avoids the domino effect and require minimum storage requirement. Most of the earlier coordinated checkpoint algorithms block their computation during checkpointing and forces minimum-process or non-blocking but forces all nodes to takes checkpoint even though many of them may not be necessary or non-blocking minimum-process but takes useless checkpoints or reduced useless checkpoint but has higher synchronization message overhead or has high checkpoint request propagation time. Hence in mobile distributed systems there is a great need of minimizing the number of communication message and checkpointing overhead as it raise new issues such as mobility, low bandwidth of wireless channels, frequently disconnections, limited battery power and lack of reliable stable storage on mobile nodes. In this paper, we propose a minimum-process coordinated checkpointing algorithm for mobile distributed system where no useless checkpoints are taken, no blocking of processes takes place and enforces a minimum-number of processes to take checkpoints. Our algorithm imposes low memory and computation overheads on MH's and low communication overheads on wireless channels. It avoids awakening of an MH if it is not required to take its checkpoint and has reduced latency time as each process involved in a global checkpoint can forward its own decision directly to the checkpoint initiator.

An Inexact Agreement protocol alows processors that each have a value approximating $\hat{\nu}$ to compute new values that are closer to each other and close to $\hat{\nu}$. Two fault-tolerant protocols for Inexact Agreement are described. As long as fewer than 1/3 of the processors are faulty, the protocols give the required convergence; they also permit iteration and thus convergence to any desired precision. When between 1/3 and 2/3 of the processors are faulty, the protocols may not converge. However, then processors either detect that too many faults have occurred or the new values computed by processors remain close to each other and to $\hat{\nu}$. In this case, the divergence is bounded. Use of the protocols for clock synchronization in a distributed system is explained.

Advanced active-safety-critical automotive applications require close coordination of different activities including sensing, processing and actuations, typically performed by different Electronic Control Units (ECU) connected over a communication network. It is imperative that ECUs executing these tasks have a common reference of time. In a distributed system, a periodic resynchronization is a common approach to ensure this. In this paper, we have proposed a new protocol for clock synchronization keeping resource-constraints automotive systems. Our specific contributions include: (a) as compared to standard treatment of drift as a linear function of time, we use a realistic non-linear model of drift, and (b) in order to minimize communication overhead, we propose an algorithm to anticipate the time at which a specific ECU would go out of sync and participate only such identified ECUs for resynchronization instead of all ECUs, as traditionally done. Analytical results show that the proposed protocol incurs minimal communication as well computational load on the ECUs.KeywordsPropagation DelayTime StampMaster NodeClock SynchronizationElectronic Control UnitThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Mobile ad hoc networks (MANETs) are infrastructureless and distributed communication systems that require sophisticated approaches to routing to cope with node mobility and heterogeneous application requirements. In the past few years, distributed hash table (DHT) has come forth as a useful additional technique to the design and specification of spontaneous and self-organized networks. Researchers have exploited its advantages by implementing it at the network layer and developing scalable routing protocols for MANETs. The implementation of DHT-based routing in a MANET requires different algorithms and specifications compared to routing in the Internet because a MANET has its unique characteristics, such as node mobility, spontaneous networking, decentralized architecture, limited transmission range, dynamic topology, and frequent network partitioning/merging. In this article, we present a comprehensive survey of research related to DHT-based routing that aims at enhancing the scalability of MANETs. We present a vivid taxonomy of DHT-based routing protocols and the guidelines to design such protocols for MANETs. We compare the features, strengths, and weaknesses of existing DHT-based routing protocols and highlight key research challenges that are vital to address. The outcome of the analysis serves as a guide for anyone willing to delve into research on DHT-based routing in MANETs.

The active nature of next generation distribution systems requires a highly accurate real-time monitoring for state estimation and situational awareness. This paper considers the problem of robust placement of a limited number of voltage magnitude meters and phasor measurement units for state estimation in an active distribution system comprising topological reconfigurations. The trace of the inverse of the Fisher information matrix is chosen as criterion for the estimation accuracy. For meter placement in a single configuration distribution system, the greedy approach provides a near-optimal solution as well as a theoretical approximation guarantee. However, for meter placement in an active distribution system, a robust approach is required to optimize the worst case estimation accuracy among all possible configurations of the system. In this paper, a simple robust algorithm, called submodular saturation algorithm, for meter placement in active distribution systems is proposed. Numerical results on three different active distribution systems show that the submodular saturation algorithm outperforms the greedy algorithm and the genetic algorithm in most cases, and provides competitive results in other cases.