Characterization, testing and reconfiguration of faults in mesh networks

Achieving fault-tolerance through incorporation of redundancy and reconfiguration is quite common. The distribution of faults can have several impacts on the effectiveness of any reconfiguration scheme; in fact, patterns of faults occurring at strategic locations may render an entire VLSI system unusable regardless of its component redundancy and its reconfiguration capabilities. Such fault patterns are called catastrophic fault patterns (CFPs). In this paper, we characterize catastrophic fault patterns in mesh networks when the links are bidirectional or unidirectional. We determine the minimum number of faults required for a fault pattern to be catastrophic. We consider the problem of testing whether a fault pattern is catastrophic. When a fault pattern is not catastrophic we study the problem of finding optimal reconfiguration strategies, where optimality is with respect to either the number of processing elements in the reconfigured network (the reconfiguration is optimal if such a number is maximized) or the number of bypass links to activate in order to reconfigure the array (the reconfiguration is optimal if such a number is minimized). The problem of finding a reconfiguration strategy that is optimal with respect to the size of the reconfigured network is NP-complete, when the links are bidirectional, while it can be solved in polynomial time, when the links are unidirectional. Considering optimality with respect to the number of bypass links to activate, we provide algorithms which efficiently find an optimal reconfiguration.     

Reliable networking in Ethernet ring mesh networks using regular topologies

Telecommunication Systems - Reliable networking is an important factor in Ethernet ring mesh networks (ERMs) with ITU-T G.8032 Ethernet ring protection recommendation or with the IEC 62439-3...     

Reliability of local area networks with bus and ring topologies

The reliability of local area networks with bus and ring topologies with a simple transfer medium are critically analysed. A double transfer medium is used to increase reliability. The efficiencies of these approaches are compared.     

Control of neuromuscular blockade in the presence of sensor faults

The problem of embedding sensor fault tolerance in feedback control of neuromuscular blockade is considered. For tackling interruptions of feedback measurements, a structure based upon Bayesian inference as well as a predictive filter is proposed. This algorithm is general and can be applied to different situations. Here, it is incorporated in an adaptive automatic system for feedback control of neuromuscular blockade using continuous infusion of muscle relaxants. A significant contribution consists in the experimental clinical testing of the algorithm in patients undergoing surgery.     

TMR voting in the presence of crosstalk faults at the voter inputs

In high reliability systems, the effectiveness of fault tolerant techniques, such as Triple-Modular-Redundancy (TMR), must be validated with respect to the faults that are likely in the current technology. In todays' Integrated Circuits (IC), this is the case of crosstalks, whose importance is growing because of device & interconnect scaling. This paper analyzes the problem of crosstalk faults at the inputs of voters in TMR systems. In particular, possible problems are illustrated, and it is shown that such crosstalk may invalidate the reliability of both voting, and diagnosing operations. The problem is analyzed from a probabilistic point of view. Its occurrence is estimated by using a set of TMR systems obtained with combinational benchmarks as functional modules. The possible problems of such operations are discussed in the presence of crosstalk faults. It is shown that crosstalk may invalidate the reliability of both voting, and diagnosis operations. A probabilistic model of the voting & diagnosis operations in the presence of crosstalk has been developed. Finally, such a model has been used to estimate the probability of voting & diagnosis failures in a set of TMR systems obtained by using combinational benchmarks as functional modules. We have shown that the presence of crosstalk faults at voter inputs may impair both the voting, and the diagnosis mechanisms. This problem has been quantified by applying a probabilistic model of crosstalk fault effects on voting and diagnosis to a set of benchmark circuits. Results show that crosstalk may create a reliability problem for TMR systems. Such a problem can be solved by using on-line testing or design for testability providing additional controllability & observability to the replicated functional units.     

Unified approach to synchronous and asynchronous approximateagreement in the presence of hybrid faults

An important problem in fault-tolerant distributed computer systems is maintaining agreement between nonfaulty processes in the presence of undiagnosed faults. Approximate agreement defines a condition in which it is not necessary for the agreed values to be numerically identical. Rather, processes need only agree with each other to within a predefined numerical tolerance. Convergent voting algorithms which achieve approximate agreement have been studied in the context of two classes of systems, synchronous and asynchronous. Studies have also addressed both completely connected and partially connected systems. Together, the two properties of synchrony and connectivity yield 4 different voting domains. In all studies to date, each voting domain has been treated as a separate problem. This paper: shows that for at least one broad family of voting algorithms, the 4 domains are special cases of a more general convergent voting problem; analyzes convergent voting under the 3-mode hybrid fault model of Thambidurai and Park; and presents a set of unifying relations applicable to all 4 voting domains. These relations are used to specify voting algorithms which optimize fault-tolerance, convergence rate, or computational overhead in any given voting domain. The task of designing a voting algorithm for a particular fault-tolerant system is thus greatly simplified     

Reliability analysis of component-level redundant topologies for solid-state fault current limiter

Experience shows that semiconductor switches in power electronics systems are the most vulnerable components. One of the most common ways to solve this reliability challenge is component-level redundant design. There are four possible configurations for the redundant design in component level. This article presents a comparative reliability analysis between different component-level redundant designs for solid-state fault current limiter. The aim of the proposed analysis is to determine the more reliable component-level redundant configuration. The mean time to failure (MTTF) is used as the reliability parameter. Considering both fault types (open circuit and short circuit), the MTTFs of different configurations are calculated. It is demonstrated that more reliable configuration depends on the junction temperature of the semiconductor switches in the steady state. That junction temperature is a function of (i) ambient temperature, (ii) power loss of the semiconductor switch and (iii) thermal resistance of heat sink. Also, results’ sensitivity to each parameter is investigated. The results show that in different conditions, various configurations have higher reliability. The experimental results are presented to clarify the theory and feasibility of the proposed approaches. At last, levelised costs of different configurations are analysed for a fair comparison.     

Reliability and cost evaluation of third-generation wireless accessnetwork topologies: a case study

The "explosive growth in bursty traffic" changes the network dynamics and requires a good evaluation of various classes of service when designing an access network. From a topological standpoint, the multiservice networks in this paper are heterogeneous systems which integrate both a core and some wireless access networks into an infrastructure similar to third-generation wireless networks. Such networks require reliable and cost-effective solutions to the problem of selecting access technologies for satisfying performance and quality of service requirements related to the services and applications envisioned. This paper analyzes the reliability aspects of some access network topologies to insure a certain level of quality of service at the lowest cost for the end users. It considers a mass market equivalent to 1.6 million subscribers, the objective being to determine the cost the users are ready to pay to benefit from services and applications provided by these multiservice networks. For these purposes, the relative behavior of 3 access-network topologies are studied: the tree with parallel backup links, the ring, and the partially meshed topologies. In ring topology, simulation results show that a great connectivity in the access network is not justified in terms of reliability requirements; the partially meshed topology, even if it has redundant links which affect its cost, outperforms the tree with parallel backup links; and the ring topology is more reliable in terms of disconnected sessions than the tree topology. By considering both reliability and cost, a tree with parallel backup links appears the best topology for the access network and its cost is acceptable for the end user. This study can be extended by: (1) establishing the cost as a function of the quality of service; (2) optimizing the partially meshed topology for more reliable networks; and (3) defining a (shaping) policy to deal with a variety of traffic schemes     

Comparison of the square-wave and quasi-resonant topologies

The waveforms of a square-wave DC-DC converter and a quasiresonant DC-DC converter are examined in detail and a comparison is made between the switching losses and conduction losses for each topology. Using data from commercially available semiconductor devices, conservative estimates are then given for the switching frequency at which the resonant approach becomes advantageous. The effect of an isolation transformer on this comparison is also addressed     

Bi-directional 2-D mesh representation for video object rendering,editing and superresolution in the presence of occlusion

In this paper, we propose a new bi-directional 2-D mesh representation of video objects, which utilizes forward and backward reference frames (keyframes). This framework extends the previous uni-directional mesh representation to enable efficient rendering, editing, and superresolution of video objects in the presence of occlusion by allowing bi-directional texture mapping as in MPEG B-frames. The video object of interest is tracked between two successive keyframes (which can be automatically or interactively selected) both in forward and backward directions. Keyframes provide the texture of the video object, whereas its motion is modeled by forward and backward 2-D meshes. In addition, we employ “validity maps”, associated with each 2-D mesh, which allow selective texture mapping from the keyframes. Experimental results for efficient video object editing and object-based video resolution enhancement in the presence of self-occlusion are presented to demonstrate the effectiveness of the proposed representation.     

Reliability and availability analysis of warm standby systems in the presence of chance with multiple critical errors

This paper presents a reliability and availability analysis of k active, N warm standby units in the presence of chance with M multiple critical errors. The system is in a failed state when (N + 1) units have failed (active and/or warm standby units have failed) or one of the multiple critical errors has occurred. Failed units are not repaired but a failed system will be repaired with repair times arbitrarily distributed. The expressions for reliability, availability and steady-state availability are derived.     

Diagnosis of single stuck-at faults and multiple timing faults in scan chains

A diagnosis technique to locate single stuck-at faults and multiple timing faults in scan chains is presented. This technique applies single excitation (SE) patterns, in which only one bit is flipped in the presence of multiple faults. With SE patterns, the problem of unknown values in scan chains is eliminated. The diagnosis result is therefore deterministic, not probabilistic. In addition to the first fault, this technique also diagnoses the remaining timing faults by applying multiple excitation patterns. Experiments on benchmark circuits show that average diagnosis resolutions are mostly less than five, even for the tenth fault in the scan chain.     

分群协议中冲突与拓扑信息误差研究

分析了实际应用中无线网络典型多址接入方式CSMA和TDMA的常见冲突,以及在网络分群结构中可能引起的拓扑信息误差,提出了度量这种拓扑信息误差的指标,并给出了几种改进措施。结合802.15.4协议实现了分群算法,并用NS2网络仿真工具分析了通信距离、移动速度对该指标的影响。     

Lee distance,Gray codes,and the torus

The torus is a topology that is the basis for the communication network of several multicomputers in use today. This paper briefly explores several topological characteristics of a generalized torus network using concepts from Coding theory and Graph theory. From Coding theory, the Lee distance metric and Gray codes are extended to mixed radix numbers. Lee distance is used to state the number and length of disjoint paths between two nodes in a torus. In addition, a function mapping a sequence of mixed radix numbers to a mixed radix Gray code sequence is described; and, provided at least one radix is even, this sequence is used to embed in the torus a cycle of any even length, including a Hamiltonian cycle. The torus is defined both as a cross product of cycles and using Lee distance. The graph-theoretic definition of a torus leads to a simple single node broadcasting algorithm, which is described in the last section. This revised version was published online in June 2006 with corrections to the Cover Date.     

Neighborhood topologies in fully informed and best-of-neighborhood particle swarms

In this study, we vary the way an individual in the particle swarm interacts with its neighbors. The performance of an individual depends on population topology as well as algorithm version. It appears that a fully informed particle swarm is more susceptible to alterations in the topology, but with a good topology, it can outperform the canonical version.     

Reliability and availability analysis of a k-out-of-N:G redundant system with repair in the presence of chance of multiple critical errors

The paper presents a reliability and availability analysis of a k-out-of-N:G redundant system with repair facilities in the presence of chance of multiple critical errors. The system is in a failed state when N−k+1 units have failed or any one of the multiple critical errors has occurred. Failed units and failed system will be repaired with constant repair rate to state with N−k+1 failed units. Laplace transforms of the state probabilities, the reliability and the availability of the system are derived. The system steady-state availability is also given.     

Basic considerations and topologies of switched-mode assistedlinear power amplifiers

This paper presents a combined power amplifier system consisting of a linear amplifier unit with a switched-mode (class D) current dumping stage arranged in parallel. With this topology, the fundamental drawback of conventional linear power amplifiers-the high loss-is avoided. Compared to a pure class D (switching) amplifier, the presented system needs no output filter to reduce the switching frequency harmonics. This filter (usually of multistage type) generally deteriorates the transient response of the system and impairs the feedback loop design. Furthermore, the low-frequency distortions of switching amplifiers caused by the interlock delay of their power transistors are avoided with the presented switched-mode assisted linear amplifier system. This can be considered as a master-slave system with a guiding linear amplifier and a supporting class D slave unit. The paper describes the operating principle of the system, analyzes the fundamental relationships for the circuit design, and presents simulation results. Finally, various further topologies of switched-mode assisted linear amplifiers are given     

Using the multilevel imbricated cells topologies in the design of low-power power-factor-corrector converters

Power-factor-corrector (PFC) converters are now commonly used in low-power supply systems connected to AC networks. In addition to their basic PFC properties, they constitute the best technical solution to directly obtain the compatibility with a large range of AC voltages provided by different distribution networks around the world (typically, from 85 to 265 V rms). It is the main application of these converters. This function is achieved with an additional cost and volume, and this extra price to pay needs to be minimized. In this context, we first recall the main approaches of the design of conventional PFCs based on the boost converter topology. We emphasize the different critical points of the sizing that mainly concern the input choke and the silicon devices, in regard with the choice of the switching frequency. Few ways of improvement are then presented for these conventional PFCs. In a second part, always in the context of a large input voltage range, we consider the possibility to introduce the multi-level concept to reduce the input choke and filters. A solution using a multi-level flying capacitor two-cell converter is presented. It is shown that it can lead to a significant increase of the performances, with several options of sizing which can be suited to different requirements of the applications.