Different Levels Of Fault Tolerance Research Articles

Distributed Application Checkpointing for Replicated State Machines

Application checkpointing is a widely used recovery mechanism that consists of saving an application's state periodically to be used in case of a failure. In this study we investigate the utilisation of distributed checkpointing for replicated state machines. Conventionally, for replicated state machines, checkpointing information is stored in a replicated way in each of the replicas or separately in a single instance. Applying distributed checkpointing provides a means to adjust the level of fault tolerance of the checkpointing approach by giving away from recovery time. We use a local cluster and cloud environment to examine the effects of distributed checkpointing in a simple state machine example and compare the results with conventional approaches. As expected, distributed checkpointing gains from memory consumption and utilise different levels of fault tolerance while performing worse in terms of recovery time.

СПОСОБИ СИНТЕЗУ ТОПОЛОГІЧНИХ ОРГАНІЗАЦІЙ НА ОСНОВІ КОДОВИХ ПЕРЕТВОРЕНЬ ДЕ БРУЙНА

Urgency of the research. Today, topological organizations such as trees, fat trees, 3D-mesh, 6D-tor, DragonFly are used as a way of network organization in data centers. All these topologies have fault-tolerant properties due to the presence of several alternative routing paths. Therefore, the task of developing new topologies that have many balanced routes (one cost path) is relevant. One of the best options for research on tree topology improvement is the combination with de Bruijn graphs in different number systems, which allows varying the degree of vertices, diameter and number of alternative paths for routing. This paper proposes a new way to obtain specified characteristics when combining tree-based topologies with a de Bruijn graph. Target setting. When creating high-performance computing systems, it is important to develop their topological organizations in advance, which allows in time to anticipate the characteristics of the system. Actual scientific researches and issues analysis. At present there are a number of works devoted to topologies based on de Bruijn sequences. There is a detailed review of the synthesis of hybrid topologies based on de Bruijn graphs and hypercube. Uninvestigated parts of general matters defining. The possibility of using hybrid topologies based on de Bruijn sequences and different types of trees remains unexamined at present. The research objective. The tasks are to develop a way to synthesize new topologies based on trees and de Bruijn sequences and to analyze the characteristics of the synthesized topological organizations for different levels of fault tolerance. The statement of basic materials. The synthesis of five topologies based on trees and de Bruijn sequences is described. A comparative analysis of all synthesized topologies is performed. Coclusions. An analysis of the characteristics is performed, the main advantages and disadvantages of the proposed topological structures are highlighted, and suggestions for their improvement are made.

Fault-Tolerant Relay Node Placement in Heterogeneous Wireless Sensor Networks

Existing work on placing additional relay nodes in wireless sensor networks to improve network connectivity typically assumes homogeneous wireless sensor nodes with an identical transmission radius. In contrast, this paper addresses the problem of deploying relay nodes to provide fault tolerance with higher network connectivity in heterogeneous wireless sensor networks, where sensor nodes possess different transmission radii. Depending on the level of desired fault tolerance, such problems can be categorized as: 1) full fault-tolerant relay node placement, which aims to deploy a minimum number of relay nodes to establish k(k ? 1) vertexdisjoint paths between every pair of sensor and/or relay nodes and 2) partial fault-tolerant relay node placement, which aims to deploy a minimum number of relay nodes to establish k(k ? 1) vertex-disjoint paths only between every pair of sensor nodes. Due to the different transmission radii of sensor nodes, these problems are further complicated by the existence of two different kinds of communication paths in heterogeneous wireless sensor networks, namely, two-way paths, along which wireless communications exist in both directions; and one-way paths, along which wireless communications exist in only one direction. Assuming that sensor nodes have different transmission radii, while relay nodes use the same transmission radius, this paper comprehensively analyzes the range of problems introduced by the different levels of fault tolerance (full or partial) coupled with the different types of path (one-way or two-way). Since each of these problems is NP-hard, we develop O(?k <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> )-approximation algorithms for both one-way and two-way partial fault-tolerant relay node placement, as well as O(?k <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> )-approximation algorithms for both one-way and two-way full fault-tolerant relay node placement (? is the best performance ratio of existing approximation algorithms for finding a minimum k-vertex connected spanning graph). To facilitate the applications in higher dimensions, we also extend these algorithms and derive their performance ratios in d-dimensional heterogeneous wireless sensor networks (d ? 3). Finally, heuristic implementations of these algorithms are evaluated via QualNet simulations.

Distributed network control for establishing reliability-constrained least-cost lightpaths in WDM Mesh networks

The trend in the development of intelligent optical networks has recently started moving towards a unified solution, to support voice, data, and various multimedia services. In this scenario different applications/end users may need different levels of fault-tolerance and differ in how much they are willing to pay for the service they get. A control scheme which is used to set up and tear down lightpaths, should not only be fast and efficient, but also be scalable. In addition, it should also try to minimize the number of blocked connections while satisfying the requested level of fault-tolerance. In this work we choose reliability of a connection as a quality of service (QoS) parameter to denote different levels of fault-tolerance. We prove that reliability-constrained least-cost (RCLC) routing problem is NP-complete and propose a distributed control scheme based on preferred link approach for establishing RCLC lightpaths. We prove the correctness of the proposed scheme and show that the scheme is flexible in that a variety of heuristics can be employed to order the neighboring links of any given node. Four heuristics are proposed and their performance is studied through extensive simulation experiments on wavelength selective networks for different network configurations. The simulation results show that our heuristics provide better performance in terms of average call acceptance rate, average path cost, average routing distance, and average connection setup time; when the connection requests with different reliability requirements arrive to and depart from the network randomly. Furthermore, if a network service provider feels that it can earn more revenue by admitting more number of calls with reliability requirements, it can do so by manipulating the parameters of our scheme, such as the maximum number of preferred links used at each node.

Differentiated QoS for survivable WDM optical networks

Optical networks based on WDM technology have become a promising solution to realize transport networks that can meet the ever-increasing demand for bandwidth. As WDM networks carry a huge volume of traffic, maintaining a high level of survivability is an important and critical issue. The. development of GMPLS switching technology led to the direct integration of IP and WDM. In these IP-over-WDM networks different applications/end users need different levels of fault tolerance and differ in how much they are willing to pay for the service they get. The current trend in network development is moving toward a unified solution providing support for voice, data, and various multimedia services. Therefore, it imperative that WDM networks incorporate fault tolerance to single or multiple component failures, protection bandwidth, recovery time, and recovery granularity besides resource utilization and call acceptance ratio. This article presents a survey of various methods that have been proposed for providing service differentiation in survivable WDM networks and discuss their performance. Such methods are broadly classified under various paradigms such as differentiated reliability, R-connections, quality of protection, and quality of recovery.

AN OPERATIONAL APPROACH TO BUDGET-CONSTRAINED RELIABILITY ALLOCATION

In this paper the problem of maximal increase of system reliability is formulated as a resource allocation problem under a budget constraint. Dynamic programing is used for the optimal solution. Time to system failure is dictated by a Markov process. The system is composed of several subsystems. Each subsystem has several possible configurations that exhibit different levels of fault tolerance and incur different incremental costs at different times. Configuration dependence among subsystems is allowed. An example resembling a fault tolerant industrial process is presented, for which the proposed algorithm is used to obtain a set of maximally reliable solutions corresponding to a set of budget constraints.