Reactive Modules

We present a formal model for concurrent systems. The model represents synchronous and asynchronous components in a uniform framework that supports compositional (assume-guarantee) and hierarchical (stepwise-refinement) design and verification. While synchronous models are based on a notion of atomic computation step, and asynchronous models remove that notion by introducing stuttering, our model is based on a flexible notion of what constitutes a computation step: by applying an abstraction operator to a system, arbitrarily many consecutive steps can be collapsed into a single step. The abstraction operator, which may turn an asynchronous system into a synchronous one, allows us to describe systems at various levels of temporal detail. For describing systems at various levels of spatial detail, we use a hiding operator that may turn a synchronous system into an asynchronous one. We illustrate the model with diverse examples from synchronous circuits, asynchronous shared-memory programs, and synchronous message-passing protocols.     

An Implementation of Constructive Synchronous Programs in POLIS

Design tools for embedded reactive systems commonly use a model of computation that employs both synchronous and asynchronous communication styles. We form a junction between these two with an implementation of synchronous languages and circuits (Esterel) on asynchronous networks (POLIS). We implement fact propagation, the key concept of synchronous constructive semantics, on an asynchronous non-deterministic network: POLIS nodes (CFSMs) save state locally to deduce facts, and the network globally propagates facts between them. The result is a correct implementation of the synchronous input/output behavior of the program. Our model is compositional, and thus permits implementations at various levels of granularity from one CFSM per circuit gate to one CFSM per circuit. This allows one to explore various tradeoffs between synchronous and asynchronous implementations.     

A Gossip-Based Energy Conservation Protocol for Wireless Ad Hoc and Sensor Networks

In this paper, we present an energy conservation scheme for wireless ad hoc and sensor networks using gossiping to place nodes in an energy saving sleep state. The technique is termed the Gossip-based Sleep Protocol (GSP). With GSP, each node randomly goes to sleep for some time with gossip sleep probability p. GSP is based on the observation that in a well connected network there are usually many paths between a source and destination, so a percentage of nodes can be in an energy conserving sleep mode without losing network connectivity. GSP needs few operations, scales to large networks and does not require a wireless node to maintain the states of other nodes. We propose two versions of GSP, one for synchronous networks and one for asynchronous networks, and afterward extend GSP to adapt to network traffic conditions. We show the advantages of the GSP approach through both simulations and analysis.     

A Study of Users’ Reactions to a Mixed Online Discussion Model: A Lag Sequential Analysis Approach

There is an increasing growth of Social Network Services (SNSs). A variety of SNSs are applied in online interpersonal platforms. Among them, asynchronous and synchronous discussions are widely examined. However, there is a lack of research into the effects of integrated discussion services that combines asynchronous and synchronous discussions. Thus, the study investigates users’ performances and behavior patterns in a mixed discussion model that integrates asynchronous and synchronous discussions with a lag sequential analysis. The results showed that most groups chose to adopt the mixed discussion model (i.e., using both synchronous and asynchronous discussions), and only one group totally adopted the asynchronous discussion model. The study further analyzed the learners’ learning effectiveness and behavioral patterns, and the results indicated that the groups using the mixed model had a positive performance to a certain extent in terms of learning effectiveness and knowledge construction. In addition, users with the mixed discussion model demonstrated diverse behaviors, which were more complex than that of those with a single-way discussion model. Furthermore, regarding the groups using “balanced synchronous and asynchronous discussions” and the groups “mainly using synchronous discussion supplemented by less asynchronous discussion” in the mixed model (simultaneously using synchronous and asynchronous discussions), those users who mainly used synchronous discussion supplemented by asynchronous discussion had more diverse behaviors of knowledge construction.     

集群环境下的并行聚类算法的通信策略

文章通过理论分析,认为可以根据并行聚类算法的时间特性来决定采用何种通信策略。对具有线性时间特性的聚类算法,可以选择同步通信方式。对具有收敛性时间特性的聚类算法,应该选择异步通信。并且通过试验,表明采用异步通信可以获得较好的性能。     

An adaptive switching scheme for iterative computing in the cloud

Delta-based accumulative iterative computation (DAIC) model is currently proposed to support iterative algorithms in a synchronous or an asynchronous way. However, both the synchronous DAIC model and the asynchronous DAIC model only satisfy some given conditions, respectively, and perform poorly under other conditions either for high synchronization cost or for many redundant activations. As a result, the whole performance of both DAIC models suffers fromthe serious network jitter and load jitter caused bymultitenancy in the cloud. In this paper, we develop a system, namely HybIter, to guarantee the performance of iterative algorithms under different conditions. Through an adaptive execution model selection scheme, it can efficiently switch between synchronous and asynchronous DAIC model in order to be adapted to different conditions, always getting the best performance in the cloud. Experimental results show that our approach can improve the performance of current solutions up to 39.0%.     

Decentralized control of distributed intelligent robots and subsystems

In a distributed robot system, asynchronous and synchronous communication between the system components is necessary to guarantee problem soliving capability in realtime. On that account, the distributed control architecure of the Karlsruhe Autonomous Mobile Robot KAMRO which is being developed at IPR has been extended by these communication kinds. The robot system consists of several subcomponents, like manipulators, two hand-eyecameras, one overhead camera and a mobile platform. To get better problem solving capability than the former centralized control architecture, these components are able to work together in teams (asynchronous communication) or special agents (synchronous communication).     

Synchronisation of linear high-order multi-agent systems via event-triggered control with limited communication

In this paper, the synchronisation problems of multi-agent systems with asynchronous and synchronous event-triggered control under a novel event-triggered condition are solved. Our event-triggered control protocols only require each agent to send its state information to its neighbouring agents when an event-triggered condition is satisfied. Such control protocols substantially reduce the cost of communication. It is worth mentioning that the proposed protocols also ensure that the synchronisation of the multi-agent system with asynchronous and synchronous event-triggered can be achieved asymptotically without Zeno-behaviour. Meanwhile, an ultimate synchronisation trajectory is given. Moreover, our results are applied to solve the formation control problem. Some numerical simulations are presented to illustrate the effectiveness of our protocols.     

Basins of attraction in fully asynchronous discrete-time discrete-state dynamic networks

This paper gives a formulation of the basins of fixed point states of fully asynchronous discrete-time discrete-state dynamic networks. That formulation provides two advantages. The first one is to point out the different behaviors between synchronous and asynchronous modes and the second one is to allow us to easily deduce an algorithm which determines the behavior of a network for a given initialization. In the context of this study, we consider networks of a large number of neurons (or units, processors, etc.), whose dynamic is fully asynchronous with overlapping updates . We suppose that the neurons take a finite number of discrete states and that the updating scheme is discrete in time. We make no hypothesis on the activation functions of the nodes, so that the dynamic of the network may have multiple cycles and/or basins. Our results are illustrated on a simple example of a fully asynchronous Hopfield neural network.     

Of Choices, Failures and Asynchrony: The Many Faces of Set Agreement

Set agreement is a fundamental problem in distributed computing in which processes collectively choose a small subset of values from a larger set of proposals. The impossibility of fault-tolerant set agreement in asynchronous networks is one of the seminal results in distributed computing. In synchronous networks, too, the complexity of set agreement has been a significant research challenge that has now been resolved. Real systems, however, are neither purely synchronous nor purely asynchronous. Rather, they tend to alternate between periods of synchrony and periods of asynchrony. Nothing specific is known about the complexity of set agreement in such a “partially synchronous” setting. In this paper, we address this challenge, presenting the first (asymptotically) tight bound on the complexity of set agreement in such systems. We introduce a novel technique for simulating, in a fault-prone asynchronous shared memory, executions of an asynchronous and failure-prone message-passing system in which some fragments appear synchronous to some processes. We use this simulation technique to derive a lower bound on the round complexity of set agreement in a partially synchronous system by a reduction from asynchronous wait-free set agreement. Specifically, we show that every set agreement protocol requires at least $\lfloor\frac{t}{k}\rfloor + 2$ synchronous rounds to decide. We present an (asymptotically) matching algorithm that relies on a distributed asynchrony detection mechanism to decide as soon as possible during periods of synchrony. From these two results, we derive the size of the minimal window of synchrony needed to solve set agreement. By relating synchronous, asynchronous and partially synchronous environments, our simulation technique is of independent interest. In particular, it allows us to obtain a new lower bound on the complexity of early deciding k-set agreement complementary to that of Gafni et al. (in SIAM J. Comput. 40(1):63–78, 2011), and to re-derive the combinatorial topology lower bound of Guerraoui et al. (in Theor. Comput. Sci. 410(6–7):570–580, 2009) in an algorithmic way.     

基于去同步技术的异步8051设计与实现

随着半导体工艺的发展,同步电路面临的时钟偏差、功耗等问题日益突出,异步设计方法得到广泛研究和关注。去同步技术可以方便地实现从同步向异步的转化,成为很有前途的异步电路设计方法。基于去同步技术设计实现了一款异步8051微控制器,着重介绍了基于去同步技术的设计流程与异步控制器设计方法。分析表明,在相同的电压、温度条件下,该异步8051性能与同步8051相当,而功耗约为1/2。     

Shared-per-wavelength asynchronous optical packet switching: A comparative analysis

This paper compares four different architectures for sharing wavelength converters in asynchronous optical packet switches with variable-length packets. The first two architectures are the well-known shared-per-node (SPN) and shared-per-link (SPL) architectures, while the other two are the shared-per-input-wavelength (SPIW) architecture, recently proposed as an optical switch architecture in synchronous context only, which is extended here to the asynchronous scenario, and an original scheme called shared-per-output-wavelength (SPOW) architecture that we propose in the current article. We introduce novel analytical models to evaluate packet loss probabilities for SPIW and SPOW architectures in asynchronous context based on Markov chains and fixed-point iterations for the particular scenario of Poisson input traffic and exponentially distributed packet lengths. The models also account for unbalanced traffic whose impact is thoroughly studied. These models are validated by comparison with simulations which demonstrate that they are remarkably accurate. In terms of performance, the SPOW scheme provides blocking performance very close to the SPN scheme while maintaining almost the same complexity of the space switch, and employing less expensive wavelength converters. On the other hand, the SPIW scheme allows less complexity in terms of number of optical gates required, while it substantially outperforms the widely accepted SPL scheme. The authors therefore believe that the SPIW and SPOW schemes are promising alternatives to the conventional SPN and SPL schemes for the implementation of next-generation optical packet switching systems.     

Consensus in the presence of mortal Byzantine faulty processes

We consider the problem of reaching agreement in distributed systems in which some processes may deviate from their prescribed behavior before they eventually crash. We call this failure model “mortal Byzantine”. After discussing some application examples where this model is justified, we provide matching upper and lower bounds on the number of faulty processes, and on the required number of rounds in synchronous systems. We then continue our study by varying different system parameters. On the one hand, we consider the failure model under weaker timing assumptions, namely for partially synchronous systems and asynchronous systems with unreliable failure detectors. On the other hand, we vary the failure model in that we limit the occurrences of faulty steps that actually lead to a crash in synchronous systems.     

Formal modelling and verification of GALS systems using GRL and CADP

A GALS (Globally Asynchronous, Locally Synchronous) system consists of several synchronous components that evolve concurrently and interact with each other asynchronously. The design of GALS systems is tedious and error-prone due to the high degree of synchronous and asynchronous concurrency present in complex architectures. In this paper, we present GRL (GALS Representation Language), a formal language designed to model GALS systems, for the purpose of formal verification of the asynchronous aspects. GRL combines the synchronous reactive model underlying dataflow languages and the asynchronous concurrent model underlying process algebras. We propose a translation from GRL to LNT, a value-passing concurrent language with classical process algebra flavour. This makes possible the analysis of GRL specifications using all the state-of-the-art simulation and verification functionalities provided by the CADP toolbox.     

Moving from Weakly Endochronous Systems to Delay-Insensitive Circuits

We consider the problem of synthesizing the asynchronous wrappers and glue logic needed for the correct GALS implementation of a modular synchronous system. Our approach is based on the weakly endochronous synchronous model, which defines high-level, implementation-independent conditions guaranteeing correct desynchronization at the level of the abstract synchronous model. We can therefore factor the synthesis problem into (1) a high-level, implementation-independent phase insuring the weak endochrony of each synchronous module and (2) the actual wrapper synthesis phase, highly simplified by the high-level assumptions, yet flexible enough to produce various, efficient implementations.We focus here on the synthesis of delay-insensitive asynchronous wrappers from weakly endochronous synchronous modules, and show how this can be done for a simple DLX processor model.     

时变复杂动力学网络的同步控制

研究时变复杂动力学网络的同步控制问题.假定网络模型中的同步轨迹及耦合配置矩阵、内部耦合矩阵的各元素均有界,当这些界值可以预估或不确定时,分别应用线性反馈控制和自适应反馈控制策略使该网络实现全局同步.通过构造Lyapunov函数,证明了对于任意初始状态的时变复杂动力学网络模型在相应的控制手段下总可以实现渐近同步.特别是设计的自适应反馈控制策略对网络的拓扑结构、节点间的耦合强度及时滞等因素表现出较强的鲁棒性.数值仿真证实了上述结论的有效性.     

Fault-tolerant control of a class of asynchronous sequential machines with permanent faults

In this note, we address a fault-tolerant control scheme for asynchronous sequential machines with permanent faults. The considered asynchronous machine is influenced by faults that change perpetually a portion of its state transition logic. If the asynchronous machine has appropriate analytic redundancy in its reachability, we can design a corrective controller so that the stable-state behavior of the closed-loop system can match that of a reference model despite occurrences of permanent faults. It is assumed that the controller is always fault-free. The existence condition and design procedure for an appropriate controller are presented based on the corrective control scheme. We also provide a controller synthesis example for validating the proposed scheme.     

Distributed event-triggered consensus for multi-agent systems with quantisation

This paper studies the consensus problem for multi-agent systems with quantised information communication via event-triggered control. First, the asynchronous event-triggered control for multi-agent systems is considered based on distributed uniform-quantised protocols. It is shown that practical consensus among agents is guaranteed and occurrence of Zeno behaviour is prevented under the designed event-triggering mechanisms. Second, under the proposed protocols using logarithmic quantised information, both synchronous and asynchronous event-triggered control algorithms are given to solve the practical consensus problem. Meanwhile, Zeno behaviour of the closed-loop systems can be excluded under the proposed event-triggered algorithms. Finally, numerical simulations are given to illustrate the effectiveness of the derived results.     

Cryptographically-enforced hierarchical access control with multiple keys

Hierarchical access control policies, in which users and objects are associated with nodes in a hierarchy, can be enforced using cryptographic mechanisms. Protected data is encrypted and authorized users are given the appropriate keys. Lazy re-encryption techniques and temporal hierarchical access control policies require that multiple keys may be associated with a node in the hierarchy. In this paper, we introduce the notion of a multi-key assignment scheme to address this requirement. We define bounded, unbounded, synchronous, and asynchronous schemes. We demonstrate that bounded, synchronous schemes provide an alternative to temporal key assignment schemes in the literature, and that unbounded asynchronous schemes provide the desired support for lazy re-encryption.     

On the power of synchronization between two adjacent processes

We study the power of local computations on labelled edges (which allow two adjacent vertices to synchronize and to modify their states simultaneaously in function of their previous states) through the classical election problem. We characterize the graphs for which this problem has a solution. As corollaries we characterize graphs which admit an election algorithm for two seminal models: Angluin’s model and asynchronous systems where processes communicate with synchronous message passing (i.e., there is a synchronization between the process sending the message and the one receiving it).