Handling multiple faults in wormhole mesh networks

Recent researches about the fault and intrusion tolerance of the complex networks take the topology or functions of the networks as benchmark. This paper shows a novel framework of the fault and intrusion tolerance of complex networks in a controllability view, which takes the number of driver nodes as standard. The result, the SF networks have a better fault tolerance than the ER networks, is consistent with the result considered with available researches. But the SF networks and ER networks have poor intrusion tolerance. The reason is that it is more difficult to fully control the real SF networks than to fully control the real ER networks, so it is easier to thoroughly destroy the controllability of the real SF networks than the real ER networks.

Cluster networks are seen as the future access networks for multimedia streaming, e-commerce, network storage, etc. For these applications, performance and high availability are particularly crucial. Regular topologies are preferred when performance is the primary concern. However, due to spatial constraints or fault-related issues, the network structure may become irregular, which makes more difficult to find deadlock-free minimal paths. Over the recent years, several solutions have been proposed. One of them is the LASH routing, which enables minimal routing by assigning paths to different virtual layers. In this paper, we propose an extension of LASH in order to reduce the number of required virtual layers by allowing transitions between virtual layers. Evaluation results show that the new routing scheme (LASH-TOR) is able to obtain full minimal routing with a reduced number of virtual channels. For torus and mesh networks, with only two virtual channels, LASH throughput is increased by an average factor of improvement of 3.30 for large networks. For regular networks with some unconnected (faulty) links, equal performance improvements are achieved. Even for highly irregular networks of size up to 128 switches the new routing scheme only needs three virtual channels for guaranteeing minimal routing. Besides, LASH-TOR performs well compared to dimension order routing for mesh and torus networks.

We propose a deterministic fault-tolerant and deadlock-free routing protocol in 2-dimensional (2-D) meshes based on dimension-order routing and the recently proposed odd-even turn model. The proposed protocol, called extended X-Y routing, does not use any virtual channels by prohibiting certain locations of faults and destinations. Faults are contained in a set of disjointed rectangular regions called faulty blocks. The number of faults to be tolerated is unbounded as long as nodes outside faulty blocks are connected in the mesh network. The extended X-Y routing can also be used under a special convex fault region called orthogonal faulty block, which can be derived from a given faulty block by activating some nonfaulty nodes in the block. Extensions to partial adaptive routing, traffic- and adaptivity-balanced using virtual networks, and routing without constraints using virtual channels and virtual networks are also discussed.

A balanced ring (b-ring) proposed by Gu et al. [Journal of Systems Architecture, 53, (2007), 902–912.] is more effective than a fault ring (f-ring) in providing fault tolerance for mesh and torus networks. By properly utilizing the b-ring, an efficient fault tolerant routing algorithm can be achieved without using any virtual channel. Traffic congestion can also be significantly reduced. However, the algorithm presented by Gu et al. for the formation of b-ring has the demerits that it involves all the nodes of the network each time a b-ring needs to be formed, and thereby increasing the overhead to the whole system. In this paper, we first present an improved algorithm for the formation of b-ring by considering only the nodes on the fault ring in contrast to all. We next present a distributed algorithm for the same, which is also based on the local knowledge, thereby avoiding overhead and thus, enhancing the overall network performances. We show that our sequential algorithm requires O(|f-ring|) time and the distributed algorithm runs in constant time.

In this paper, following our recent developed concept of subnet model in mesh networks, we continue to investigate the characterizations of probabilistic fault tolerance for the mesh networks with faulty node. We consider two fault models: each node has deterministic or stochastic failure probability, then we study the fault tolerance of mesh networks based on our novel technique - subnet model. We derive lower bounds on the connectivity probability for mesh networks. Our study shows that mesh networks of practical size can tolerate a large number of faulty nodes thus are reliable enough for multicomputer systems under deterministic or stochastic node failure probability. Comparing with deterministic node failure probability, stochastic model is close to realistic case.

Compressionless Routing (GR) is a new adaptive routing framework which provides a unified framework for efficient deadlock-free adaptive routing and fault-tolerance. CR exploits the tight-coupling between wormhole routers for flow control to detect potential deadlock situations and recover from them. Fault-tolerant Compressionless Routing (FCR) extends Compressionless Routing to support end-to-end fault-tolerant delivery. Detailed routing algorithms, implementation complexity and performance simulation results for CR and FCR are presented.CR has the following advantages: deadlock-free adaptive routing in torus networks with no virtual channels, simple router designs, order-preserving message transmission, applicability to a wide variety of network topologies, and elimination of the need for buffer allocation messages. FCR has the following advantages: tolerates transient faults while maintaining data integrity (nonstop fault-tolerance), tolerates permanent faults, can be applied to a wide variety of network topologies, and eliminates the need for software buffering and retry for reliability. These advantages of CR and FCR not only simplify hardware support for adaptive routing and fault-tolerance, they also can simplify communication software layers.

Failures are normal rather than exceptional in cloud computing environments, high fault tolerance issue is one of the major obstacles for opening up a new era of high serviceability cloud computing as fault tolerance plays a key role in ensuring cloud serviceability. Fault tolerant service is an essential part of Service Level Objectives (SLOs) in clouds. To achieve high level of cloud serviceability and to meet high level of cloud SLOs, a foolproof fault tolerance strategy is needed. In this paper, the definitions of fault, error, and failure in a cloud are given, and the principles for high fault tolerance objectives are systematically analyzed by referring to the fault tolerance theories suitable for large-scale distributed computing environments. Based on the principles and semantics of cloud fault tolerance, a dynamic adaptive fault tolerance strategy DAFT is put forward. It includes: (i) analyzing the mathematical relationship between different failure rates and two different fault tolerance strategies, which are checkpointing fault tolerance strategy and data replication fault tolerance strategy; (ii) building a dynamic adaptive checkpointing fault tolerance model and a dynamic adaptive replication fault tolerance model by combining the two fault tolerance models together to maximize the serviceability and meet the SLOs; and (iii) evaluating the dynamic adaptive fault tolerance strategy under various conditions in large-scale cloud data centers and consider different system centric parameters, such as fault tolerance degree, fault tolerance overhead, response time, etc. Theoretical as well as experimental results conclusively demonstrate that the dynamic adaptive fault tolerance strategy DAFT has high potential as it provides efficient fault tolerance enhancements, significant cloud serviceability improvement, and great SLOs satisfaction. It efficiently and effectively achieves a trade-off for fault tolerance objectives in cloud computing environments.

Fault tolerance is one of the most important issues for the design of cost-effective and high performance interconnection networks. In this paper, a new fault tolerance routing algorithm for n-dimensional meshes is presented. The presented algorithm is based on a planer fault model which only disables minimum fault-free nodes to form rectangular fault regions. The algorithm uses three virtual channels per physical channel and only employs a very simple deadlock avoidance scheme. In spit the variety fault regions in n-dimensional mesh, the presented algorithm is always connected as long as fault regions do not disconnect the network. The result of simulation shows that the proposed routing algorithm is of feasibility of gracefully degraded operation.

Numerous researchers have suggested numerous solutions based on routing and energy to overcome the prevalence of WSN faults in the current literature. Clustering is the most commonly used energy-efficient and fault-tolerant management technique in WSNs, grouping sensors to manage them and perform distributed activities such as resource management. Although clustering methods are most commonly used to reduce energy consumption, they can also achieve various quality-driven goals, such as network fault tolerance capability. As a result of WSN's unpredictable nature, developing fault tolerance mechanisms is essential. Redundancy and diversity methods are commonly used in networks to increase fault tolerance. As a network management challenge, clustering methods should tolerate malfunctioning sensors while maintaining the network's coverage and stability. Sensors are prone to failure due to their operation in hostile environments with limited battery power. The state of the deployed sensor or cluster head (CH) can be active, redundant, or dead/faulty for the same target region of interest (R). The network's overall lifetime and fault tolerance capability can also be extended by using these backup sensors. By putting redundant sensors into sleep mode, can extend the network lifetime without compromising the quality of service. Sensor networks are generally designed to endure far longer than individual sensors. It is commonly performed by putting sensors to sleep. We propose a robust distributed clustered fault tolerance scheduling (RDCFT) approach that efficiently checks the status of the deployed sensor periodically (based on a sweep-line redundancy check algorithm) in WSNs. Simulation results are based on analytical and experimental studies to validate the effectiveness and usefulness of the proposed work.

Due to adverse effects of hostile deployment environment(s), sensors nodes (SNs) deployed in the network may drain or get damaged. This attributes for loss of connectivity between the sensors and the sink node. Hence it is necessary to design the wireless sensor network (WSN) in a manner that the network is capable of coping up with the failure of few nodes/links. Using single hop data communication model reduces the lifetime of the network as the SNs are resource constrained (in terms of battery). Relay nodes (RNs) facilitate in improving network lifetime, fault tolerance and/or connectivity. Finding minimum number of relay nodes for a fault tolerant, fully connected network is a NP Hard problem. In this paper, we follow two phase relay node placement procedure to achieve the objective. In the first phase, we cluster the SNs using mean shift algorithm and place RNs as the cluster heads. In the second phase, we use metaheuristic algorithms like Moth Flame Optimization (MFO), Differential Evolution (DE), Bat algorithm (BA) and Biogeography Based Optimization algorithm (BBO) to place the RNs such that the required fault tolerance is achieved along with fully connected network. Extensive simulation results prove that MFO algorithm performs better for fault tolerant relay node placement problem.

We explore basic necessary protocols to achieve tolerance for quantum computation in the cluster state and circuit models. For the cluster state model we simulate the implementation of an arbitrary rotation via only measurement on a decohered cluster state. Fidelity is used to quantify the accuracy of the initial cluster state and a gate fidelity for the arbitrary rotation is determined. In the circuit model we compare the accuracy of two methods that can be used to construct a logical zero state appropriate for the [7, 1, 3] Steane quantum error correction code in a non-equiprobable Pauli operator error environment: a tolerant method done by applying error correction on seven qubits all in the state zero, and a non-fault tolerant method done by implementing the encoding gate sequence. We find that the latter construction method, in spite of its lack of fault tolerance, outputs a seven qubit state with a higher fidelity than the first (fault tolerant) method. However, the fidelity of the single qubit of stored information exhibits almost equivalent values between the two construction methods.

This article examines the functioning of sensor networks as a key component of the Internet of Things (IoT) technology, which facilitates integration between the physical and digital worlds. It analyzes the challenges sensor networks face, including limited resources, node failures, scalability, and security threats. The main components of sensor networks are discussed: sensors, smart elements, gateways, and communication modules that enable data collection and transmission for further analysis. Attention is drawn to the fact that sensor networks are often targets of malicious attacks, such as DDoS, Sinkhole, and routing attacks, which necessitate the development of new protection methods. The paper thoroughly examines threats from illegitimate elements in sensor networks that can disrupt network operations, cause data leaks, and affect network resilience and fault tolerance by exhausting resources. To effectively detect such nodes, it is proposed to apply mechanisms for traffic analysis, energy consumption monitoring, and encryption. The nature of failures in sensor networks and the interrelationship between fault tolerance and security are explored. Probabilities of failure for networks of different sizes are calculated, and mechanisms for improving fault tolerance, including node redundancy, self-healing algorithms, and fault tolerance mechanisms, are proposed. A methodology for detecting malicious nodes based on traffic and energy characteristics analysis is suggested. It was found that nodes exceeding threshold values for the number of transmitted packets or energy consumption may be malicious. It is noted that combining various methods will improve the accuracy of detecting malicious nodes at early stages, significantly enhancing the level of information security in sensor networks. Prospects for further research into the development of new protective mechanisms and improvements in the fault tolerance of sensor networks are highlighted.

Talking out the network issues, the switching techniques specify the connection activities performed by the switching elements when a message is received at the input port. Traditional switching mechanisms such as Wormhole Switching (WS) realize high performance, but prone to deadlock in the vicinity of faults. While some techniques such as adaptive routing can alleviate the problem, it cannot solve the problem by itself. This has motivated the development of different switching techniques. The Scouting Switching (SS) has been suggested as an efficient switching mechanism for reconciling the confliction demands on communication performance and fault-tolerance in interconnection networks. Although SS has been around for years and it can greatly benefit from adaptive routing as it reduces blocking in the network, there has been hardly any attempt to provide an analytical model for SS when fully adaptive routing along with virtual channels is used. Besides, mesh is one of the most desirable topologies regarding to characteristics which can offer very good scalability. In an effort to fill this gap, this paper proposes the first analytical model for 2-D mesh networks using SS augmented with virtual channels. Experimental results show that this model is able to predict message latency with a good degree of accuracy.

The emergence of Cloud Computing has brought new dimension to the world of information technology. Even though Cloud Computing provide various benefits like agility, on-demand provisioning of resources, reduced cost, multi-tenancy etc., there are risks and flaws associated with it. One key research challenge in Cloud Computing is to ensure continuous reliability and guaranteed availability of resources provided by it. So there is a need for a robust Fault Tolerant (FT) system in Cloud Computing. To better understand FT in Cloud Computing, it is essential to understand the different types of faults. In this paper, we highlight the basic concepts of fault tolerance by understanding the different FT policies like Reactive FT policy and Proactive FT policy and the associated FT techniques used on different types of faults. A study on various fault tolerant methods, algorithms, frameworks etc., has been carried out which are developed and implemented by research experts in this field. This is an area where lot of research is happening and these studies will guide us to build a robust FT technique in Cloud.

Fault tolerance (FT) is a topic of major concern in achieving dependable systems, for both real time as well as non real time systems. The paper provides a model of achieving fault tolerance, based on the ISO/ITU Reference Model for Open Distributed Processing (RM-ODP). This reference model provides a system software engineering methodology for fault tolerance, an object based model of fault tolerance, system requirements for achieving fault tolerance in an open manner, modeling constructs and rules to enable a proper system specification of fault tolerance, and business rules in terms of policies to achieve a well formed system specification. All these aspects are discussed at some depth, but the author primarily focuses on how certain behavior can be specified and achieved in an object based system, the constructs of the Unified Modeling Language (UML) and the Object Constraint Language (OCL).