Implementing a sidechain-based asynchronous DPKI

1 Introduction Public key infrastructure(PKI)is an integral part of the network communication system.Relying on the certificate authority,it provides security policies for the systems,which enables users to communicate or conduct e-commerce transactions in a trustworthy relationship.Centralized PKI(CPKI)has been providing the netizens with security services and maintaining the privacy for decades.     

高性能的异步复制系统的设计

为了提高整个远程复制系统的性能,对卷复制系统进行了优化.采用了多线程并行处理技术和流水线技术,设计了一种高性能的日志和位图,采用了网络自适应的复制协议和高效的请求合并策略.实验结果表明,该优化策略减少了应用等待的时间,降低了网络发送的时间开销,合理利用了有限的复制带宽,提高了复制效率.     

远程异步复制系统的数据多缓冲方法

提出了一种在远程异步复制系统(remote asynchronous replication system,RARS)中的数据多缓冲方法.该方法主要包括基于Windows基本卷[3]的海量缓存模型和基于内存的发送缓冲模型.给出了海量缓存和发送缓冲的定义和实现方法,并对该方法进行了性能测试和分析.实验结果表明,该方法解决了磁盘读写速度与网络数据传输速度不匹配的问题,同时不影响本地数据中心数据备份服务的高可用性.     

A Transactional Asynchronous Replication Scheme for Mobile Database Systems

In mobile database systems,mobility of users has a significant impact on data replication.As a result,the various replica control protocols that exist today in traditional distributed and multidatabase environments are no longer suitable To solve this problem,a new mobile database replication scheme,the Transaction-Level Result-Set Propagation(TLRSP)model,is put forward in this paper,The conflict dectction and resolution strategy based on TLRSP is discussed in detail,and the implementation algorithm is proposed,In order to compare the performance of the TLRSP model with that of other mobile replication schemes,we have developed a detailde simulation model.Experimantal results show that the TLRSP model provides an effcient support for replicated mobile database systems by reducing reprocessing overhead and maintaining database consistency.     

Using adaptive scheduling for increased resiliency in passive asynchronous replication

Distributed systems commonly replicate data to enhance system dependability. In such systems, a logical update on a data item results in a physical update on a number of copies. The synchronization and communication required to keep the copies of replicated data consistent introduce a delay when operations are performed. In systems distributed over a bandwidth-constrained area, such operational delays generally prove unacceptable and passive asynchronous replication is often used to mitigate the delays. The research described in this paper looks to develop a new methodology for passive asynchronous replication that includes the introduction of an adaptive data replication scheduler to increase the data redundancy of the most valued data objects in overloaded situations. The approach we describe relies on the batch processing nature of passive asynchronous replication to make update decisions based on a defined policy. The methodology uses an adaptive scheduling algorithm providing near real-time selection of which objects to replicate during overloaded conditions based on a trained multilayer perceptron neural network. Historical replication logs are used for the initial training of the network and supervised training continues as replication logs are created providing periodic improvement through a feedback mechanism. This paper presents summary results of data replication scheduling simulations with an emphasis on the design selection of the adaptive distributed scheduler. This research was supported in part by a research fellowship from the Naval Surface Warfare Center, Dahlgren Division. The views, opinions, and findings contained herein are those of the authors and should not be construed as an official Department of Defense position, policy, or decision.     

ADOPT-ing: unifying asynchronous distributed optimization with asynchronous backtracking

This article presents an asynchronous algorithm for solving distributed constraint optimization problems (DCOPs). The proposed technique unifies asynchronous backtracking (ABT) and asynchronous distributed optimization (ADOPT) where valued nogoods enable more flexible reasoning and more opportunities for communication, leading to an important speed-up. While feedback can be sent in ADOPT by COST messages only to one predefined predecessor, our extension allows for sending such information to any relevant agent. The concept of valued nogood is an extension by Dago and Verfaille of the concept of classic nogood that associates the list of conflicting assignments with a cost and, optionally, with a set of references to culprit constraints. DCOPs have been shown to have very elegant distributed solutions, such as ADOPT, distributed asynchronous overlay (DisAO), or DPOP. These algorithms are typically tuned to minimize the longest causal chain of messages as a measure of how the algorithms will scale for systems with remote agents (with large latency in communication). ADOPT has the property of maintaining the initial distribution of the problem. To be efficient, ADOPT needs a preprocessing step consisting of computing a Depth-First Search (DFS) tree on the constraint graph. Valued nogoods allow for automatically detecting and exploiting the best DFS tree compatible with the current ordering. To exploit such DFS trees it is now sufficient to ensure that they exist. Also, the inference rules available for valued nogoods help to exploit schemes of communication where more feedback is sent to higher priority agents. Together they result in an order of magnitude improvement.     

Atomic broadcast in asynchronous crash-recovery distributed systems and its use in quorum-based replication

Atomic broadcast is a fundamental problem of distributed systems: It states that messages must be delivered in the same order to their destination processes. This paper describes a solution to this problem in asynchronous distributed systems in which processes can crash and recover. A consensus-based solution to atomic broadcast problem has been designed by Chandra and Toueg for asynchronous distributed systems where crashed processes do not recover. We extend this approach: it transforms any consensus protocol suited to the crash-recovery model into an atomic broadcast protocol suited to the same model. We show that atomic broadcast can be implemented requiring few additional log operations in excess of those required by the consensus. The paper also discusses how additional log operations can improve the protocol in terms of faster recovery and better throughput. To illustrate the use of the protocol, the paper also describes a solution to the replica management problem in asynchronous distributed systems in which processes can crash and recover. The proposed technique makes a bridge between established results on weighted voting and recent results on the consensus problem.     

Optimal anticipative scheduling with asynchronous transmissionopportunities

Service is provided to a set of parallel queues by a single server. The service of queue i may be initiated only at certain time instances {t_nⁱ}_n=1^∞ that constitute the connectivity instances for queue i. The service of different customers cannot overlap. Scheduling is required to resolve potential contention of services initiated at closely spaced, closer than the service time, connectivity instances. At any time t, the future connectivity instances are available for scheduling. An anticipative policy is given, which at time t schedules the transmissions until a certain future time t+h. The length of the scheduling horizon h is selected based on the backlog at t. The allocation of the server in the interval [t, t+h], is done in accordance to the backlogs of the individual queues at t. The throughput region of the system is characterized, and it is shown that the policy we propose achieves maximum throughput. The policy has a low implementation complexity which is bounded for all the achievable throughput vectors. The average delay and the scheduling complexity are studied by simulation, and the trade-off between the two is demonstrated. The above scheduling problem arises in the access layer of the cross-links of a satellite network     

Synthesising an asynchronous DMA controller with Balsa

A DMA controller has been designed and implemented as part of the AMULET3i asynchronous microprocessor macrocell using a mixture of synchronous and asynchronous circuit techniques. The synthesis language Balsa has been used to implement the major part of the controller, the asynchronous control. The use of Balsa has allowed the controller to be rapidly re-engineered in response to a changing specification.     

Implementing dataflow with threads

A general algorithm is presented for implementing dataflow computations with multiple threads that communicate using only reads and writes of shared memory.     

Performing work with asynchronous processors: Message-delay-sensitive bounds

This paper considers the problem of performing tasks in asynchronous distributed settings. This problem, called Do-All, has been substantially studied in synchronous models, but there is a dearth of efficient algorithms for asynchronous message-passing processors. Do-All can be trivially solved without any communication by an algorithm where each processor performs all tasks. Assuming p processors and t tasks, this requires work Θ (p · t). Thus, it is important to develop subquadratic solutions (when p and t are comparable) by trading computation for communication. Following the observation that it is not possible to obtain subquadratic work when the message delay d is substantial, e.g., d = Θ (t), this work pursues a message-delay-sensitive approach. Here, the upper bounds on work and communication are given as functions of p, t, and d, the upper bound on message delays, however, algorithms have no knowledge of d and they cannot rely on the existence of an upper bound on d. This paper presents two families of asynchronous algorithms achieving, for the first time, subquadratic work as long as d = o (t). The first family uses as its basis a shared-memory algorithm without having to emulate atomic registers assumed by that algorithm. These deterministic algorithms have work O (tp^ε + pdt/d^ε) for any ε > 0. The second family uses specific permutations of tasks, with certain combinatorial properties, to sequence the work of the processors. These randomized (deterministic) algorithms have expected (worst-case) work O (t log p + pd log (2 + t/d)). Another important contribution in this work is the first delay-sensitive lower bound for this problem that helps explain the behavior of our algorithms: any randomized (deterministic) algorithm has expected (worst-case) work of Ω (t + pd log_d+1t).     

Efficient asynchronous federated learning with sparsification and quantization

While data is distributed in multiple edge devices, federated learning (FL) is attracting more and more attention to collaboratively train a machine learning model without transferring raw data. FL generally exploits a parameter server and a large number of edge devices during the whole process of the model training, while several devices are selected in each round. However, straggler devices may slow down the training process or even make the system crash during training. Meanwhile, other idle edge devices remain unused. As the bandwidth between the devices and the server is relatively low, the communication of intermediate data becomes a bottleneck. In this article, we propose time-efficient asynchronous federated learning with sparsification and quantization, that is, TEASQ-Fed. TEASQ-Fed can fully exploit edge devices to asynchronously participate in the training process by actively applying for tasks. We utilize control parameters to choose an appropriate number of parallel edge devices, which simultaneously execute the training tasks. In addition, we introduce a caching mechanism and weighted averaging with respect to model staleness to further improve the accuracy. Furthermore, we propose a sparsification and quantitation approach to compress the intermediate data to accelerate the training. The experimental results reveal that TEASQ-Fed improves the accuracy (up to 16.67% higher) while accelerating the convergence of model training (up to twice faster).     

改进的基于智能卡的远程异步认证协议

远程认证协议允许远程服务器和用户通过不安全信道实现相互认证。唐宏斌等指出Chen等方案的基于智能卡的远程认证协议存在着一些安全问题,如丢失智能卡攻击,重放攻击等,并且提出一种基于智能卡的远程认证协议,为了抵抗重放攻击而引入时间戳机制。提出一种改进的基于智能卡的远程异步认证方案,在能抵抗提到的所有攻击条件下,不需要考虑时钟同步问题而能抵抗重放攻击,使操作更简单且未增加计算性能代价。     

Fault-containing self-stabilization in asynchronous systems with constant fault-gap

This paper presents a new transformation which adds fault-containment properties to silent self-stabilizing algorithms. The transformation features a constant slow-down factor and the fault-gap—that is the minimal time between two containable faults—is also constant. The transformation scales well to arbitrarily large systems and avoids global synchronization. The presented transformation is the first with a constant fault-gap and requires no knowledge of the system size.     

Timing analysis of MSC specifications with asynchronous concatenation

Message Sequence Chart (MSC) is a graphical and textual language for describing the interactions between system components, and MSC specifications (MSSs) are a combination of a set of basic MSCs (bMSCs) and a High-level MSC that describes potentially iterating and branching system behavior by specifying the compositions of basic MSCs, which offer an intuitive and visual way of specifying design requirements. With concurrent, timing, and asynchronous properties, MSSs are amenable to errors, and their analysis is important and difficult. This paper deals with timing analysis of MSC specifications with asynchronous concatenation. For an MSC specification, we require that for any loop, its first node be flexible in execution time and its any associated external timing constraint be enforced on the entire loop. Such an MSC specification is called a flexible loop-closed MSC specification (FLMSS). We show that for FLMSSs, the reachability analysis and bounded delay analysis problems can be solved efficiently by linear programming. The solutions have been implemented into our tool TASS and evaluated by experiments.     

Faster asynchronous systems

A testing scenario in the sense of De Nicola and Hennessy is developed to measure the worst-case efficiency of asynchronous systems. The resulting testing-preorder is characterized with a variant of refusal traces and shown to satisfy some properties that make it attractive as a faster-than relation. Finally, one implementation of a bounded buffer is shown to be strictly faster than two others – in contrast to a result obtained with a different approach by Arun-Kumar and Hennessy.     

Model-driven development of asynchronous message-driven architectures with AsyncAPI

In the Internet-of-Things (IoT) vision, everyday objects evolve into cyber-physical systems. The massive use and deployment of these systems has given place to the Industry 4.0 or Industrial IoT (IIoT). Due to its scalability requirements, IIoT architectures are typically distributed and asynchronous. In this scenario, one of the most widely used paradigms is publish/subscribe, where messages are sent and received based on a set of categories or topics. However, these architectures face interoperability challenges. Consistency in message categories and structure is the key to avoid potential losses of information. Ensuring this consistency requires complex data processing logic both on the publisher and the subscriber sides. In this paper, we present our proposal relying on AsyncAPI to automate the design and implementation of these asynchronous architectures using model-driven techniques for the generation of (part of) message-driven infrastructures. Our proposal offers two different ways of designing the architectures: either graphically, by modeling and annotating the messages that are sent among the different IoT devices, or textually, by implementing an editor compliant with the AsyncAPI specification. We have evaluated our proposal by conducting a set of experiments with 25 subjects with different expertise and background. The experiments show that one-third of the subjects were able to design and implement a working architecture in less than an hour without previous knowledge of our proposal, and an additional one-third estimated that they would only need less than two hours in total.

     

Integrating synchronous and asynchronous collaboration with virtualnetwork computing

With thin-client virtual network computing technology, the support for synchronous collaboration offered by traditional CSCW tools has been extended to asynchronous participation in a shared workspace. Using frame buffer rectangles to relay pixel values, the system considered acquires and stores the ongoing computer session and offers all participants a joint viewing of their shared workspace. The system also forwards input from the real-time conferees to the remote session and offers support for teleoperations from multiple distributed users. It also lets latecomers retrieve and play back parts of the session they have missed with VCR-like control (fast forward, rewind, play, and stop). Distributed users can access the remote session from heterogeneous platforms such as X Window or Windows NT, or with a Web browser such as Netscape