Synchronous Message Research Articles

Two-hop time synchronization protocol for sensor networks

One of the critical middleware services for sensor networks is the time synchronization, which provides supports to different applications. Synchronization protocols used for Internet and LANs are not appropriate in the sensor networks for the high-density and limited energy resource. This paper describes two-hop time synchronization (TTS) that aims at reducing the synchronization overhead and providing more accurate network-wide synchronization. The synchronization message exchanges are minimized by making full use of sensors’ broadcast domain and enlarging the common node synchronization range in multi-hop scenarios. By halving synchronization hops, the TTS achieves high multi-hop synchronization precision. The proposed protocol contains single-hop synchronization model, multi-hop synchronization algorithm, and a power control scheme. We prove that the extension of single-hop TTS to network-wide synchronization is NP-complete. The complexity and convergence time of multi-hop TTS are analyzed in detail. We simulate TTS on MATLAB and show that it requires minimal overhead and convergence time compared with other protocols. We also implement TTS on common sensors and its multi-hop synchronization error is less than that of receiver-receiver synchronization (R-RS).

An enhanced (t,n) threshold directed signature scheme

A directed signature scheme is devised to achieve directivity for verification such that only a designated verifier can check the validity of a signature and, in times of trouble, any third party can verify the signature with the help of the signer or the designated verifier. A threshold directed signature scheme distributes responsibility and authority for generating a directed signature to several users via a threshold mechanism. Lu et al. recently proposed a novel (t,n) threshold directed signature scheme. In this paper, we show that the scheme is vulnerable to a rogue-key attack which is mounted by an adversary who can arbitrarily select his or her public key. Through the rogue-key attack, the adversary can forge a signature on any message for a set of signers. In order to thwart such a rogue-key attack, we propose an enhanced (t,n) threshold directed signature scheme with a reliable key registration protocol. The protocol guarantees that a user should have access to the secret key corresponding to the user’s public key. Under the computational Diffie-Hellman assumption, we prove that the improved scheme is secure, that is, it achieves existential unforgeability under the chosen message attack, invisibility, and transitivity in the registered key model. We stress that the security of our improved scheme does not depend on a specific broadcast channel for synchronous message transmission.

Pronto: A Low Overhead Message Passing System for High Performance Many-Core Processors

Many-core processors provide the raw computation power required by modern high-performance multimedia and signal processing workloads. The conversion of this computation power into ex- ecution performance is often constrained by the overheads of communication between concurrent tasks. This paper presents Pronto, a low overhead message passing system which simplies the semantics of data movement between communicating tasks by performing buffer management, message synchronization and address translation directly in hardware. The integration of these functions into hardware results in transfer latencies upto 30% shorter than state of the art MPI derivatives. The overheads for communication with Pronto in an 18-core processor array are under 5% for 64-word burst transfers, and less than 0.5% of total execution time using workloads such as the JPEG decoder and FIRlter. Furthermore, this paper also studies the effect of task mapping and interconnect traffic on the predictability of data block arrival times, and provides insight on where interconnect contention can be tolerated.

Minimum mutable checkpoint-based coordinated checkpointing protocol for mobile distributed systems

Coordinated checkpointing is an attractive approach to add fault tolerance to mobile distributed systems transparently against various predictable and unexpected faults. This approach avoids domino effect and require minimum stable storage but may require additional synchronisation messages and blocking. Coordinated checkpointing overhead can be minimised either by minimising processes to checkpoint or by making checkpointing process non-blocking. In literature it has been reported that there cannot be a minimum process non-blocking coordinated checkpointing protocol. Minimisation of processes to checkpoint for an initiation can be combined with non-blocking by taking some additional checkpoints that may be discarded on completion of the checkpoint protocol unnecessary checkpoints. Such checkpoints are called mutable if stored on local memory of mobile host temporarily. In this paper, we investigated this problem further and designed an efficient coordinated checkpointing protocol that is non-blocking, requires coordination of only minimum number of processes and reduces the overhead of unnecessary checkpoints significantly. Simulation studies show that our protocol reduces the number of unnecessary checkpoints almost to zero.

Time Synchronization for Heterogeneous WSNs Based on Cluster

Aiming at that there are some heterogeneous nodes in special applications, time synchronization algorithm for heterogeneous WSNs based on cluster (TSBC) is proposed in this paper. In every round of TSBC, time synchronization is started by sink node, every heterogeneous node sends cluster head request message to sink node when it receives the time synchronization start message, and take itself as a cluster head when it receives the acknowledgement sent by sink node. Then, every cluster head broadcasts elected message in the net, common nodes select the nearest cluster head as their cluster head and join the cluster. Time synchronization begins firstly between sink node and cluster heads, and then begins between cluster heads and common nodes. The components of transmitting delay of synchronization message between sender and receiver are analyzed and computed, consequently, the time offset of nodes are obtained, and the frequency drift are computed by linear regression method. Simulation results indicate that TSBC has higher synchronization ratio and synchronization precision, longer lifetime and lower energy consumption than FTSP in heterogeneous WSNs.

A MapReduce Iteration Framework in Local Parallel and Message Synchronization

With the development of large-scale distributed computing, Stand-alone operating environment to meet the demand of the time and space overhead of massive data based on. There is more attention to how to design the distributed algorithm for efficient cloud computing environment. The MapReduce model cannot solve the issue. In this paper, the redesign of the computing model of MapReduce, ensure the existing calculation models compatible with the old MapReduce operation. At the same time, the framework used the message synchronization mechanism to implement state data changing interaction tasks in Parallel Layer. Compared to the original MapReduce operation, greatly reduces the processing time of the MapReduce iterative algorithm.

The development of synchronous text-based instant messaging as an online interviewing tool

The article reports the development of a synchronous text-based online interviewing tool with a continuity of private discussion that is not achieved in open-ended questionnaires, email interviews and online discussion boards. The participants were women who had undergone a surgical or natural menopause, who in a pilot interview highlighted the potential sensitivity of this subject and inspired the implementation of this method. The overall feedback was positive with the main advantages centred on feelings of anonymity, convenience and a more comfortable interview environment. Disadvantages included lack of body language and technical issues with computers. This technique ensures a degree of confidentiality while still obtaining depth of enquiry, where other qualitative methods potentially risk invading a participant’s privacy. It can be offered both alongside other interviewing techniques to allow participant choice and on its own when exploring sensitive and personal topics or when extra participant anonymity is appropriate.

The Research of Clock Traffic Congestion Model and Synchronization Technology

Considering the limited bandwidth, delay and the flow of mutual association, the greater the flow, the delay lags the more obvious; when flow close to saturation, delay will become very serious. According to the PTP local clock offset correction mechanism; this paper proposed an adaptive routing algorithm based on through node flow congestion forecast message. The method based on least squares support vector machine on the discharge time series online regression estimate future period of time clock node network flow value, from this investigation clock node congestion degree index, so the choice of adaptability PTP since the minimum delay routing, improve the synchronous message delivery success rate, reduce the complex network of synchronous accuracy vulnerable data flow congestion hysteresis effect.

Measurement and modeling of paging channel overloads on a cellular network

IP and cellular networks used to be isolated from each other. In recent decade however, the two networks have started to overlap with the emergence of devices that access the Internet using cellular infrastructures. One important question then is whether actions or threats on the Internet side can impact the telecom or cellular side. We address this problem in the paper and specifically consider the paging channel, which is a key conduit shared by both Internet and cellular traffic. Our contributions are as follows: we illustrate through experiments on a CDMA2000 cellular network that attacks launched from the Internet can significantly increase the paging load and increase the delay of paging messages including cellular call setup requests; we derive a simple but accurate queuing model for the paging system in a CDMA2000 network and use this model to demonstrate that the paging channel exhibits sharp rather than graceful degradation under load; and through this model, we identify critical parameters that impact paging performance. Although our study is focused on CDMA2000 networks, similar problems exist in other types of cellular networks that employ a single control channel with limited bandwidth for both synchronous and asynchronous control messages.

Application of Web 2.0 Tools in IIT (Indian Institute of Technology) & IIM (Indian Institute of Management) Libraries of India: a Study

Internet‟s rapid growth and broad penetration, along with affordable enabling Web 2.0 technologies, has not only democratized access to information but also catalyzed open access publishing which has contributed to the explosion of freely available digital information. The paper describes how the IIT and IIM Libraries provide access to their collection and user support for all that access using Web 2.0 technologies such as synchronous messaging and streaming media, blogs, wiki and social networking.

Improving Communication Patterns for Distributed Cluster-based Individual-oriented Fish School Simulations

Parallel discrete event simulation (PDES) have shown to be an useful paradigm for simulating complex and large-scale models. An individual-oriented approach allows modelers capture complex emerging global behaviors generated by simple local interaction, like observed in self-organized systems. Usually, this type of simulations are highly expensive in terms of computing and communications. One one hand, we can reduce the computing involved in individual interactions by means of developing a robust partitioning method. On the other hand, we have to be able to efficiently handle a huge number of individuals interacting with other individuals stored in memory of remote processors. In this work we will analyze and compare three communication strategies: synchronous and asynchronous message passing (via MPI) and bulk-synchronous parallel (BSP) for our distributed cluster-based individual-oriented fish school simulator. In this type of simulations, the main contributions of our work are: a) we showed that distributed time-driven simulations do not always improve the performance when using synchronous communication strategies, b) we show asynchronous communications strategies are more efficient. In addition, we have verified that the bulk-synchronous parallel method is a scalable.

Does cooperative e-learning improve graduate student project outcomes?

Cooperative learning was applied in an online graduate project management course to compare the effectiveness of asynchronous versus synchronous online team meetings. A quasi-experiment was constructed to allocate students to project teams while ensuring there was a balance of requisite skills, namely systems analysis and design along with HTML/Javascript programming. The project was constructed with a level of difficulty that required cooperative learning for high marks. The treatment in the experiment required the control group to use an asynchronous discussion forum for project meetings, and the test group to use synchronous video, audio, and text messaging for their team meetings. Prior ability was measured and numerous experimental controls were imposed.

Optimistic parallelism based on speculative asynchronous message passing

This article proposes a new speculative multi-threading execution model for object-oriented programs. Using this model, sequential object-oriented programs are partitioned into multiple speculative object threads according to their structure and semantics by compiler and runtime system. Object threads that serve as the basic unit of the parallel target code are dynamically mapped onto thread units of the target machine. However, synchronous message passing between objects in a source program prevents parallel execution of object threads in the target code at synchronous points. By speculating the execution of message passing in object-oriented programs, we can convert synchronous message passing into speculative asynchronous message passing. This enables us to decrease synchronization overhead in runtime and to exploit greater parallelism for such programs. The runtime system verifies speculative asynchronous message passing by comparing it with non-speculative synchronous message passing so that parallel execution remains predictable and deterministic. This model was implemented as a prototype system, Rope, for evaluation. Experiments with a Java version of the Olden benchmark suite showed that the proposed model exhibits excellent accelerating effects for object-oriented programs.

A Distributed O(1)-Approximation Algorithm for the Uniform Facility Location Problem

We investigate a metric facility location problem in a distributed setting. In this problem, we assume that each point is a client as well as a potential location for a facility and that the opening costs for the facilities and the demands of the clients are uniform. The goal is to open a subset of the input points as facilities such that the accumulated cost for the whole point set, consisting of the opening costs for the facilities and the connection costs for the clients, is minimized. We present a randomized distributed algorithm that computes in expectation an ${\mathcal {O}}(1)$ -approximate solution to the metric facility location problem described above. Our algorithm works in a synchronous message passing model, where each point is an autonomous computational entity that has its own local memory and that communicates with the other entities by message passing. We assume that each entity knows the distance to all the other entities, but does not know any of the other pairwise distances. Our algorithm uses three rounds of all-to-all communication with message sizes bounded to $\mathcal{O}(\log(n))$ bits, where n is the number of input points. We extend our distributed algorithm to constant powers of metric spaces. For a metric exponent l≥1, we obtain a randomized ${\mathcal {O}}(1)$ -approximation algorithm that uses three rounds of all-to-all communication with message sizes bounded to $\mathcal{O}(\log(n))$ bits.

Exploring asynchronous and synchronous tool use in online courses

While the independent contributions of synchronous and asynchronous interaction in online learning are clear, comparatively less is known about the pedagogical consequences of using both modes in the same environment. In this study, we examine relationships between students' use of asynchronous discussion forums and synchronous private messages (PM). We find that asynchronous notes contain more academic language and less social language, are more difficult to read, and are longer compared to PM. In addition, we find that the most active forum-posters are also the most active PM users, suggesting that PMing is not reducing their contribution to public discourse. Finally, we find that those who frequently PM are less likely to rapidly scan forum notes, and that they spend more time online than those who make less use of PM. We suggest that PM supports asynchronous discussions in the formation of a community of inquiry. ► Little is known about combining synchronous and asynchronous communication. ► The most active synchronous students tend also to be most active asynchronously. ► Synchronous communication supports the exchange of social content. ► Synchronous and asynchronous communication play complementary, supporting roles.

Semiconductor lasers driven by self-sustained chaotic electronic oscillators and applications to optical chaos cryptography

In this work, we numerically study the dynamics of vertical cavity surface emitting laser (VCSEL) firstly when it is driven by Chua's oscillator, secondly in case where it is driven by a broad frequency spectral bandwidth chaotic oscillator developed by Nana et al. [Commun. Nonlinear Sci. Numer. Simul. 14, 2266 (2009)]. We demonstrated that the VCSEL generated robust chaotic dynamics compared to the ones found in VCSEL subject to a sinusoidally modulated current and therefore it is more suitable for chaos encryption techniques. The synchronization characteristics and the communication performances of unidirectional coupled VCSEL driven by the broad frequency spectral bandwidth chaotic oscillators are investigated numerically. The results show that high-quality synchronization and transmission of messages can be realized for suitable system parameters. Chaos shift keying method is successfully applied to encrypt a message at a high bitrate.

HIGH THROUGHPUT OF ASYNCHRONOUS TRAFFIC AND MAXIMUM CAPACITY OF SYNCHRONOUS SOURCES WITH THE NEW FDDI'S MAC PROTOCOL

It is well known that Fiber Distributed Data Interface (FDDI) offers an excellent cost-benefit and guarantees a reliable and powerful network. It is also fact that the FDDI is suitable for synchronous traffic because of the high speed and the performance guarantees it provides. However, these guarantees are achieved at the expense of asynchronous traffic because the synchronous messages are given highest priority over asynchronous messages, resulting in excessive delays and low throughput for asynchronous message. This paper, presents a modification of the FDDI's MAC(Media Access Control) protocol to control the maximum token rotation time not to exceed the TTRT (Target Token Rotation Time) in the worst case, the realization of this condition leads to set the TTRT to the message generation period (Tg) instead of one half of it (Tg/2). The new protocol of FDDI’s MAC increasing both the throughput of asynchronous traffic and the capacity of synchronous sources. The proposed MAC is evaluated by means of computer simulation. The simulation results confirm that the new proposed MAC provides FDDI more efficient for supporting multimedia applications.

Oh! Web 2.0, Virtual Reference Service 2.0, Tools & Techniques (II)

The paper describes the theory and definition of the practice of librarianship, specifically addressing how Web 2.0 technologies (tools) such as synchronous messaging, collaborative reference service and streaming media, blogs, wikis, social networks, social bookmarking tools, tagging, RSS feeds, and mashups might intimate changes and how libraries provide access to their collections and user support for that access.

Adaptive Time Synchronization for Homogeneous WSNs

Wireless sensor networks (WSNs) are being used for observing real-world phenomenon. It is important that sensor nodes (SNs) must be synchronized to a common time in order to precisely map the data collected by SNs. Clock synchronization is very challenging in WSNs as the sensor networks are resource constrained networks. It is essential that clock synchronization protocols designed for WSNs must be light weight i.e. SNs must be synchronized with fewer synchronization message exchanges. In this paper, we propose a clock synchronization protocol for WSNs where first of all cluster heads (CHs) are synchronized with the sink and then the cluster nodes (CNs) are synchronized with their respective CHs. CNs are synchronized with the help of time synchronization node (TSN) chosen by the respective CHs. Simulation results show that proposed protocol requires considerably fewer synchronization messages as compared with the reference broadcast synchronization (RBS) protocol and minimum variance unbiased estimation (MUVE) method. Clock skew correction mechanism applied in proposed protocol guarantees long term stability and hence decreases re-synchronization frequency thereby conserving more energy.

A novel efficient power‐saving MAC protocol for multi‐hop MANETs

SUMMARYFollowing recent advances in the performance of ad hoc networks, the limited life of batteries in mobile devices poses a bottleneck in their development. Consequently, how to minimize power consumption in the Medium Access Control (MAC) layer of ad hoc networks is an essential issue. The power‐saving mode (PSM) of IEEE 802.11 involves the Timing Synchronization Function to reduce power consumption for single‐hop mobile ad hoc networks (MANETs). However, the IEEE 802.11 PSM is known to result in unnecessary energy consumption as well as the problems of overheating and back‐off time delay. Hence, this study presents an efficient power‐saving MAC protocol, called p‐MANET, based on a Multi‐hop Time Synchronization Protocol, which involves a hibernation mechanism, a beacon inhibition mechanism, and a low‐latency next‐hop selection mechanism for general‐purpose multi‐hop MANETs. The main purposes of the p‐MANET protocol are to reduce significantly the power consumption and the transmission latency. In the hibernation mechanism, each p‐MANET node needs only to wake up during one out of every N beacon interval, where N is the number of beacon intervals in a cycle. Thus, efficient power consumption is achieved. Furthermore, a beacon inhibition mechanism is proposed to prevent the beacon storm problem that is caused by synchronization and neighbor discovery messages. Finally, the low‐latency next‐hop selection mechanism is designed to yield low transmission latency. Each p‐MANET node is aware of the active beacon intervals of its neighbors by using a hash function, such that it can easily forward packets to a neighbor in active mode or with the least remaining time to wake up. As a consequence, upper‐layer routing protocols can cooperate with p‐MANET to select the next‐hop neighbor with the best forwarding delay. To verify the proposed design and demonstrate the favorable performance of the proposed p‐MANET, we present the theoretical analysis related to p‐MANET and also perform experimental simulations. The numerical results show that p‐MANET reduces power consumption and routing latency and performs well in extending lifetime with a small neighbor discovery time. Copyright © 2011 John Wiley & Sons, Ltd.