Fault-tolerant real-time communication in distributed computingsystems

The delivery delay in a point-to-point packet switching network is difficult to control due to the contention among randomly-arriving packets at each node and multihops a packet must travel between its source and destination. Despite this difficulty, there are an increasing number of applications that require packets to be delivered reliably within prespecified delay bounds. This paper shows how this can be achieved by using real-time channels which make “soft” reservation of network resources to ensure the timely delivery of real-time packets. We first present theoretical results and detailed procedures for the establishment of real-time channels and then show how the basic real-time channels can be enhanced to be fault-tolerant using the multiple disjoint paths between a pair of communicating nodes. The contribution of the former is a tighter schedulability condition which makes more efficient use of network resources than any other existing approaches, and that of the latter is a significant improvement in fault tolerance over the basic real-time channel, which is inherently susceptible to component failures     

Fault-tolerant communication algorithms in toroidal networks

Fault-tolerant communication algorithms for k-ary n-cubes are introduced. These include: One-to-all broadcasting, all-to-all broadcasting, one-to-all personalized communication, and all-to-all personalized communication. Each of these algorithms can tolerate up to (2n-2) node failures provided that k>(2n-2) and k>3. Extensions of these algorithms with up to 2n-1 node failures are also described. The communication complexities of the proposed algorithms are derived when wormhole or store and forward packet routing is used     

Hard real-time communication in multiple-access networks

With the increasing use of distributed hard real-time systems, the ability of computer networks to handle hard real-time message traffic is becoming more important. For traditional networks, maximizing the throughput or minimizing the average message delay is the most important performance criteria. In the hard real-time domain, however, concern focuses on satisfying the time constraints of individual messages. This paper examines recent developments in hard real-time communication in local area multiple-access networks. Two general strategies are used in hard real-time communication: the guarantee strategy and the best-effort strategy. In the former, messages are guaranteed to meet their deadlines during normal operation of the network. In the best-effort strategy, the network will attempt to send messages before their deadlines, but no guarantees are given. Real-time message traffic can be distinguished according to whether it is best suited for the guarantee strategy or the best-effort strategy. Although this paper concentrates on multiple-access networks, many of the concepts presented and lessons learned are also applicable to other types of networks.     

Guaranteed real-time communication in packet-switched networks with FCFS queuing

In this paper, we propose a feasibility analysis of periodic hard real-time traffic in packet-switched networks using first come first served (FCFS) queuing but no traffic shapers. Our work constitutes a framework that can be adopted for real-time analysis of switched low-cost networks like Ethernet without modification of the standard network components. Our analysis is based on a flexible network and traffic model, e.g., variable-sized frames, arbitrary deadlines and multiple switches. The correctness of our real-time analysis and the tightness of it for network components in single-switch networks are given by theoretical proofs. The performance of the end-to-end real-time analysis is evaluated by simulations. Moreover, our conceptual and experimental comparison studies between our analysis and the commonly used Network Calculus (NC) shows that our analysis can achieve better performance than NC in many cases.     

Fault-tolerant communication in embedded supercomputing

A framework consisting of reusable modules acting at different levels can provide fault tolerance mechanisms for synchronous and asynchronous communication to ensure coherence of parallel tasks     

Fault-tolerant stabilisation in double-integrator networks

This article considers a network of agents with double-integrator internal dynamics, which share pieces of information on their position states. For such a system, a fault-tolerant decentralised stabilisation problem is addressed. The goal consists in placing the closed-loop poles in the open left-half of the complex plane, even in the presence of faults of the transmitting and receiving apparatuses of one or more agents. By exploiting some previous results on fault-tolerant control, a necessary and sufficient condition for the problem to admit a solution is proved. Further, an explicit formula is given for the local regulators, which can be taken of the first-order, actually the least one. Finally, the theory is extended to networks of agents with multiple-integrator internal dynamics.     

Experimental evaluation of behavior-based failure-detection schemesin real-time communication networks

Effective detection of failures is essential for reliable communication services. Traditionally, non-real-time computer networks have relied on behavior-based techniques for detecting communication failures. That is, each node uses heartbeats to detect the failure of its neighbors and the end-to-end transport protocol (e.g., TCP) achieves reliable communication by acknowledgment/retransmission. Recently, there has been a growing demand for reliable “real-time” communication, but little research has been done on the failure detection problem. In this paper, we present two behavior-based failure-detection schemes-neighbor detection and end-to-end detection-for reliable real-time communication services and experimentally evaluate their effectiveness. Specifically, we measure and analyze the coverage and latency of these detection schemes through fault-injection experiments. The experimental results have shown that nearly all failures can be detected very quickly by the neighbor detection scheme, while the end-to-end detection scheme uncovers the remaining failures with larger detection latencies     

Fault-tolerant communication with partitioned dimension-orderrouters

The current fault-tolerant routing methods require extensive changes to practical routers such as the Cray T3D's dimension-order router to handle faults. In this paper, we propose methods to handle faults in multicomputers with dimension-order routers with simple changes to router structure and logic. Our techniques can be applied to current implementations in which the router is partitioned into multiple modules and no centralized crossbar is used. We consider arbitrarily located faulty blocks and assume only local knowledge of faults. We apply our techniques for torus networks and show that, with as few as four virtual channels per physical channel, deadlock- and livelock-free routing can be provided even with multiple faults and multimodule implementation of routers. Our simulations of the proposed technique for 2D tori and mesh indicate that the performance degradation is similar to that seen in the case of cross-bar based designs previously proposed     

Fault-tolerant scheduling for real-time embedded control systems

With the increasing complexity of industrial application, an embedded control system (ECS) requires processing a number of hard real-time tasks and needs fault-tolerance to assure high reliability. Considering the characteristics of real-time tasks in ECS, an integrated algorithm is proposed to schedule real-time tasks and to guarantee that all real-time tasks are completed before their deadlines even in the presence of faults. Based on the nonpreemptive critical-section protocol (NCSP), this paper analyzes the blocking time introduced by resource conflicts of relevancy tasks in fault-tolerant multiprocessor systems. An extended schedulability condition is presented to check the assignment feasibility of a given task to a processor. A primary/backup approach and on-line replacement of failed processors are used to tolerate processor failures. The analysis reveals that the integrated algorithm bounds the blocking time, requires limited overhead on the number of processors, and still assures good processor utilization. This is also demonstrated by simulation results. Both analysis and simulation show the effectiveness of the proposed algorithm in ECS.     

Fault-tolerant adaptive scheduling for embedded real-time systems

Describes a fault-tolerant algorithm which uses a time-value scheduling approach to detect faults, sustain high processor utilization, and ensure timely execution of critical tasks     

Fault-tolerant and real-time scheduling for mixed-criticality systems

The design and analysis of real-time scheduling algorithms for safety-critical systems is a challenging problem due to the temporal dependencies among different design constraints. This paper considers scheduling sporadic tasks with three interrelated design constraints: (i) meeting the hard deadlines of application tasks, (ii) providing fault tolerance by executing backups, and (iii) respecting the criticality of each task to facilitate system’s certification. First, a new approach to model mixed-criticality systems from the perspective of fault tolerance is proposed. Second, a uniprocessor fixed-priority scheduling algorithm, called fault-tolerant mixed-criticality (FTMC) scheduling, is designed for the proposed model. The FTMC algorithm executes backups to recover from task errors caused by hardware or software faults. Third, a sufficient schedulability test is derived, when satisfied for a (mixed-criticality) task set, guarantees that all deadlines are met even if backups are executed to recover from errors. Finally, evaluations illustrate the effectiveness of the proposed test.     

Fault-tolerant de Bruijn and shuffle-exchange networks

This paper addresses the problem of creating a fault-tolerant interconnection network for a parallel computer. Three topologies, namely, the base-2 de Bruijn graph, the base-m de Bruijn graph, and the shuffle-exchange, are studied. For each topology an N+k node fault-tolerant graph is defined. These fault-tolerant graphs have the property that given any set of k node faults, the remaining N nodes contain the desired topology as a subgraph. All of the constructions given are the best known in terms of the degree of the fault-tolerant graph. We also investigate the use of buses to reduce the degrees of the fault-tolerant graphs still further     

Fault-tolerant wormhole routing for hypercube networks

We present an adaptive fault-tolerant wormhole routing algorithm for hypercubes by using 3 virtual networks. The routing algorithm can tolerate at least n−1 faulty nodes and can route a message via a path of length no more than the shortest path plus four. Previous algorithms which achieve the same fault tolerant ability need 5 virtual networks. Simulation results are also given in this paper.     

一种传感器网络容错拓扑控制算法

基于对局部最小生成树拓扑控制算法的研究,提出了对该算法改进的容错拓扑控制算法。通过广播来收集节点的局部信息构造局部最小生成树,并通过深度优先搜索算法使得任意两节点间至少存在K（K=2,3）条内部节点互不相交的路径,保证网络的K连通和容错特性。仿真结果表明：该算法降低了网络的功耗,提高例了网络的容量,网络的容错性能和生存能力都有了较大的提高。     

Multi-hop cellular networks: Architecture and protocols for best-effort and real-time communication

Until recently, research on cellular networks concentrated only in single-hop cellular networks. The demand for high throughput has driven to architectures that use multiple hops in the presence of infrastructure. We propose an architecture for multihop cellular networks (MCNs). MCNs combine the benefits of having a fixed infrastructure of base stations and the flexibility of Ad hoc networks. They are capable of achieving much higher throughput than current cellular systems, which can be classified as single-hop cellular networks (SCNs). In this work, we propose an extended architecture for MCN using the IEEE 802.11 standard for wireless LANs for connection-less service and a TDMA-based solution for real-time support. We provide a general overview of the architecture and the issues involved in the design of MCNs, in particular the challenges to be met in the design of a routing protocol, a channel assignment scheme, and a mobility management scheme. We also propose a routing protocol called Base-Assisted Ad hoc Routing (BAAR) protocol for use in such networks and a model for the performance analysis of MCNs and SCNs. We also conduct extensive experimental studies on the performance of MCNs and SCNs under various load (TCP, UDP, and real-time sessions) and mobility conditions. These studies clearly indicate that MCNs with the proposed architecture and routing protocol are viable alternatives for SCNs, in fact they provide much higher throughput. MCNs are very attractive for best-effort packet radio where they can achieve an increase in throughput up to four when compared to similar SCNs. But for real-time traffic, even though they do outperform SCNs, they also suffer from a few disadvantages such as frequent hand-offs and throughput degradation at high mobility. We also present results from a detailed comparison study of our architecture for MCN with the Hybrid Wireless Network (HWN) architecture and Integrated Cellular Ad hoc Relaying (iCAR) Architecture.     

Fault-tolerant analysis of a class of networks

In this paper, we explore the 2-extraconnectivity of a special class of graphs G(G₀,G₁;M) proposed by Chen et al. [Y.-C. Chen, J.J.M. Tan, L.-H. Hsu, S.-S. Kao, Super-connectivity and super edge-connectivity for some interconnection networks, Applied Mathematics and Computation 140 (2003) 245-254]. As applications of the results, we obtain that the 2-extraconnectivities of several well-known interconnection networks, such as hypercubes, twisted cubes, crossed cubes, Möbius cubes and locally twisted cubes, are all equal to 3n−5 when their dimension n is not less than 8. That is, when n?8, at least 3n−5 vertices must be removed to disconnect any one of these n-dimensional networks provided that the removal of these vertices does not isolate a vertex or an edge.     

异构分布式实时系统的容错优化调度算法

针对分布式实时系统,在分析了单处理调度算法的基础上,结合版本复制技术和首次适应方法,给出了一种容错调度算法。分析了算法的可调度性,给出任务的可调度性条件。在满足任务容错可调度的情况下,以提高处理器的利用率为目标,对基版本时限进行了优化,给出了基版本优化时限的求取算法。仿真结果表明,本文算法将可以得到比FTEDFFF和FTRMFF更高的处理器利用率。     

一种容错的传感器网络数据融合隐私保护算法

由于网络通信具有易错的特点,提出一种具有容错性的隐私保护数据聚集算法。通过椭圆曲线加密方案对节点数据进行加密,保证数据的隐私性,采用加同态加密技术,实现了端到端的聚集加密,节省能耗和带宽。同时,构造轨道图拓扑结构,使得每个节点有多个父节点,当节点与主父节点发生链路失效时,其他父节点能够修复聚集值。仿真实验结果显示,提出的方案在适当增加通信量的情况下,具有较高的数据安全性、很好的容错性和高精度的聚集值。     

可重构系统中实时任务容错调度算法

现在FPGA已被广泛的应用,但三模冗余(TMR)结构不能充分利用FPGA资源,基于主/从版本技术,提出一种实时任务容错调度算法。算法通过后向调度从版本,使得从版本在其截止期限内尽可能地推迟执行,从而同一任务的主从版本在执行时间上没有重叠或较少重叠,当任务主版本成功执行时释放任务从版本所占用的资源。仿真实验表明,与TMR相比,此方法能更有效地利用FPGA资源,提高硬件任务的接受率。     

Fault-tolerant design for wide-area Mobile IPv6 networks

Mobile IPv6 provides the mobility management for IPv6 protocol. To establish a reliable Mobile IPv6 network, fault tolerance should be also considered in the network design. This paper presents an efficient fault-tolerant approach for Mobile IPv6 networks. In the proposed approach, if a failure is detected in the home agent (HA) of a mobile node, a preferable survival HA is selected to continuously serve the mobile node. The preferable survival HA is the HA that does not incur failure and is neighboring the current location of the mobile node. The proposed approach is based on the preference of each mobile node to achieve the fault tolerance of the HA. Finally, we perform simulations to evaluate the performance of the proposed approach.