Network Reliability

Free Space Optic (FSO) communication systems have the great potential of serving as high bandwidth links. However, their popularity and widespread use is limited by the fact, that this technology is dependent upon an unobstructed line of sight more than any other wireless communication system. Especially weather conditions affecting visibility, such as fog or heavy rain, often cause unacceptable link failures. To increase reliability, a variety of hybrid FSO/RF systems has been introduced, among them a great number of switch-over systems. These systems require an accurate and timely detection of link failure and an appropriate algorithm to react. Generally, the received signal strength is considered as an indicator for link quality. Fluctuations in this indicator prohibit the use of simple threshold comparison techniques. In this paper, a set of switch-over algorithms is introduced and analyzed, using attenuation measurement data of fog events.

The reachability of a strongly connected network may be destroyed after link damage. Since many networks have directed links with the potential for reversal, the reachability may be restored by reversing the direction of links. In this paper, the reliability of a network that allows reversal of links is discussed.

In this part, the problem is clearly defined from a practical point of view. A general multi stage mathematical programming formulation of the problem addressing the shortcomings is presented. The complexity issues of this general formulation is also addressed and discussed. Finally, we propose a directed graph, minimum edge cost network flow modeling of the problem for a truly multi stage formulation that would guarantee global optimality. Results form a simple test case based on the proposed formulation is presented and analyzed.

Based on VANETs (Vehicle Ad-hoc Networks), a stable, reliable and low delay wireless network access environment is an inevitable element of vehicle safety applications. The IEEE 802.11p is a specially designed protocol for ITS (Intelligent Transportation Systems) for V2V and V2I communication. It provides 10 MHz channel bandwidth and up to 27-Mbps data transmission rate. This paper analyzes the theoretical throughput and delay limit of the 802.11p protocol. Considering PLR (Packet Loss Rate) and delay of VANETs, we analyzed the theoretical highway capacity upper limit of 802.11p for V2V communication. The results show that 802.11p communication technology can increase highway capacity. If all of the vehicles are equipped with 802.11p communication technology, the increase in highway capacity is about 491 percent.

We investigate the problem of provisioning shared-mesh-protected sub-wavelength connections in wavelength-convertible optical WDM networks. We propose protection-at-lightpath (PAL) level and protection-at-connection (PAC) level. We found PAL outperforms PAC in such network settings.

In P2P systems, each peer has to obtain information of other peers and propagate the information to other peers through neighboring peers. Thus, it is important for each peer to have some number of neighbor peers. Moreover, it is more significant to discuss if each peer has reliable neighbor peers. In reality, each peer might be faulty or might send obsolete, even incorrect information to the other peers. We have implemented a P2P platform called JXTA-Orverlay, which defines a set of protocols that standardize how different devices may communicate and collaborate among them. It abstracts a new layer on the top of JXTA through a set of primitive operations and services that are commonly used in JXTA-based applications and provides a set of primitives that can be used by other applications, which will be built on top of the overlay, with complete independence. JXTA-Overlay provides a set of basic functionalities, primitives, intended to be as complete as possible to satisfy the needs of most JXTA-based applications. In this paper, we present two fuzzy-based systems (called FRS1 and FRS2) to improve the reliability of JXTA-Overlay P2P platform. We make a comparison study between the fuzzybased reliability systems. Comparing the complexity of FRS1 and FRS2, the FRS2 is more complex than FRS1. However, it considers also the security; therefore, it can be used in real application for secure systems.

We propose two versions of Link Failure Probability (LFP) based backup resource sharing algorithms, namely LFP based First-Fit algorithm, and LFP based Best-Fit algorithm for Generalized Multi-Protocol Label Switching networks. Customers' availability requirements are met by adjusting the availability of the protection paths with different sharing options. Information required for calculating the availability of both the working, and protection paths can be collected along the specific working, and protection paths, thus avoiding the requirement for flooding. This makes our algorithms scalable for a large network. Our algorithms work consistently against both single, and multiple failures. Furthermore, we propose extensions for the existing signaling protocols to demonstrate that our proposed algorithms require minimum changes to the existing protocols. Simulation results show that our proposal performs better than the conventional Dedicated Path Protection schemes in terms of Call Acceptance Rate, and Total Bandwidth Consumption. Finally, by comparing simulation results to analytical results for a simplified network, we provide some insights into the correctness, and efficiency of our proposed algorithms.

Network performance and reliability are crucial in the digital age, where seamless service delivery is a competitive advantage. Site Reliability Engineering (SRE) is a field developed to improve system reliability through engineering approaches, with Network Performance Monitoring and Diagnostic Analysis (NPMD) serving as fundamental practices to achieve this goal. This paper explores the architecture and methodology of NPMD, integrating SRE principles with key metrics like SLIs, SLOs, and Non-Functional Requirements (NFRs). By examining real-time monitoring, diagnostics, and the role of automation in network reliability, this paper provides a technical foundation for implementing NPMD practices within SRE frameworks to enhance network resilience and performance.

The calculation of network reliability in a probabilistic context has long been an issue of practical and academic importance. Conventional approaches (determination of bounds, sums of disjoint products algorithms, Monte Carlo evaluations, studies of the reliability polynomials, etc.) only provide approximations when the network's size increases, even when nodes do not fail and all edges have the same reliability p. We consider here a directed, generic graph of arbitrary size mimicking real-life long-haul communication networks, and give the exact, analytical solution for the two-terminal reliability. This solution involves a product of transfer matrices, in which individual reliabilities of edges and nodes are taken into account. The special case of identical edge and node reliabilities (p and ρ, respectively) is addressed. We consider a case study based on a commonly-used configuration, and assess the influence of the edges being directed (or not) on various measures of network performance. While the two-terminal reliability, the failure frequency and the failure rate of the connection are quite similar, the locations of complex zeros of the two-terminal reliability polynomials exhibit strong differences, and various structure transitions at specific values of ρ. The present work could be extended to provide a catalog of exactly solvable networks in terms of reliability, which could be useful as building blocks for new and improved bounds, as well as benchmarks, in the general case.

The two-and all-terminal reliabilities of the Brecht-Colbourn ladder and the generalized fan have been calculated exactly for arbitrary size as well as arbitrary individual edge and node reliabilities, using transfer matrices of dimension four at most. While the all-terminal reliabilities of these graphs are identical, the special case of identical edge (p) and node (ρ) reliabilities shows that their two-terminal reliabilities are quite distinct, as demonstrated by their generating functions and the locations of the zeros of the reliability polynomials, which undergo structural transitions at ρ = 1 2 .

This paper present news trends for electric DC microgrids for smart Homes and smart cities. With the emergence of the renewable energies, the DC bus could optimize electricity power efficiency for smart home (green home). Since the initial choice for alternative current transportation in 1880, the electrical architecture distributions haven't been change with one direction distribution to the consumers through high voltage lines. But AC power distribution therefore is so wasteful due to number of converters AC/AC and AC/DC with consequent energy losses (15% energy per converter). Nowadays most of renewable energy sources as solar panel are DC and all modern appliances are also DC powered (LED lighting, IT, electric car ..). We propose a smart DC grid distribution architecture for smart homes based on 2 voltages levels 48 VDC (Power over Ethernet) and 380 to 400 HVDC bus to improve electrical efficiency. Under the scope of ANR-C3µ project we present a microgrid DC bus with distributed control command for optimal energy resources management based on self-consumption and peak shaving for the grid. For data exchanges we will use Power Line Communication (PLC) now widely used in wide range of AC application (IP over AC) for the DC line and to pilot the DC microgrid. With the expérimental results feedback we could analyze the communications performances and the design for a microgrid control/command system in smart building applications.

In real-time mixed-critical systems, Worst-Case Execution Time (WCET) analysis is required to guarantee that timing constraints are respected—at least for high-criticality tasks. However, the WCET is pessimistic compared to the real execution time, especially for multicore platforms. As WCET computation considers the worst-case scenario, it means that whenever a high-criticality task accesses a shared resource in multicore platforms, it is considered that all cores use the same resource concurrently. This pessimism in WCET computation leads to a dramatic underutilization of the platform resources, or even failing to meet the timing constraints. In order to increase resource utilization while guaranteeing real-time guarantees for high-criticality tasks, previous works proposed a runtime control system to monitor and decide when the interferences from low-criticality tasks cannot be further tolerated. However, in the initial approaches, the points where the controller is executed were...

Abstract: A new methodology for water resources systems reliability evaluation is presented. The proposed methodology considers both: mechanical reliability (probability of pipe failure) and reliability of hydraulic parameters in the nodes and links (pressure, velocity). On the ...

At first sight, aiming for energy efficiency appears to penalize electricity carriers. A close look at electrical energy flow, from primary to final energy, reveals abysmally low efficiency, resulting from the generation mix, transmission and distribution losses, and obsolete equipment. As a consequence, the share of primary electricity has to be reduced in order to achieve low carbon society scenarios in line with energy saving policies. Since it relies on a partial description of the electrical workflow, this viewpoint reveals certain weaknesses that need to be qualified with a long-term planning assessment. We propose circumventing this drawback using a thermodynamic analysis based on the Gibbs free energy of the electromagnetic field. In particular, the so-called Maxwell-Faraday law of induction is the local result of an optimal path towards reversibility of the entire power system, described as a monotherm engine. This approach supports a multi-scale analysis that naturally addresses those levels that involve huge losses, namely the functional materials, conversion devices and transmission network. As a result, the role played by magnetic energy is clarified: although it is required locally for conversion purposes, magnetic energy's overall value governs the transmission of electrical power through the grid. In addition to indicating kinetic reserve, an evaluation of the power system's reliability should include an assessment of magnetic energy from the very first moment of fluctuation (typically a few ms).

Among various measures of network reliability, an important reliability measure is the probability that all nodes of the network are connected by up-state links showing a measure that indicates the extent to which the network can be used. Spanning trees and sum-of-disjoint product approach is one of the ways of evaluating this reliability measure. The purpose of this paper is to provide a new dimension to the computation of global reliability in undirected networks by defining and using g-minimal cut sets with SDP based multi-variable inversion (MVI) technique without any requirement of complex mathematics or graph-theory concepts. These cut sets turns out to be much less than the number of spanning tress. The paper presents an algorithm to enumerate such g-minimal cut sets with an illustrative example. Besides, it provides results for several other networks to show the efficacy of the proposed approach.

This paper present news trends for electric DC microgrids for smart Homes and smart cities. With the emergence of the renewable energies, the DC bus could optimize electricity power efficiency for smart home (green home). Since the initial choice for alternative current transportation in 1880, the electrical architecture distributions haven't been change with one direction distribution to the consumers through high voltage lines. But AC power distribution therefore is so wasteful due to number of converters AC/AC and AC/DC with consequent energy losses (15% energy per converter). Nowadays most of renewable energy sources as solar panel are DC and all modern appliances are also DC powered (LED lighting, IT, electric car ..). We propose a smart DC grid distribution architecture for smart homes based on 2 voltages levels 48 VDC (Power over Ethernet) and 380 to 400 HVDC bus to improve electrical efficiency. Under the scope of ANR-C3µ project we present a microgrid DC bus with distributed control command for optimal energy resources management based on self-consumption and peak shaving for the grid. For data exchanges we will use Power Line Communication (PLC) now widely used in wide range of AC application (IP over AC) for the DC line and to pilot the DC microgrid. With the expérimental results feedback we could analyze the communications performances and the design for a microgrid control/command system in smart building applications.

Business firms undertake economic activities with motivational objective of profit maximization and revenue growth. In addition, the firms also make approaches to assess production processes in their effort to explore efficient ways of production. We consider economic growth analysis of the production process of the firms as an approach for exploring efficient technique of production. The production function which describes mechanism of economic growth shows the relationship between the input and output resources of the firm. The wireless telecom network of BSNL is considered in this paper as a model network for analyzing the characteristics of the economic growth namely – growth caused by increase in input volume and growth caused by increase in productivity. In Manipur, most of the telecom service providers face challenges of poor network reliability because of scarcity of grid energy supply at their base stations.  However, simulation study on network traffic reveals that even at...

The network availability of the wireless network can be viewed as broader concept of network reliability. Reliability is a unique quality of wireless network and it is regarded as key parameter for business success of the telecom service providers. The network availability however is often compromised with outages caused by various factors and amongst the factors, inadequate energy at the base stations is the major outage-contributing factor. Due to unreliable electrical grid supply at many base stations, diesel generators are deployed to the stations as an alternative source of energy.  The diesel generators incur high operating expenses. This paper presents a quantitative approach for measurement and estimation of diesel fuel consumption based on uptime hours of various equipments installed at the base station site. It also introduces a new parameter called energy conservation factor, which determines amount of energy transfer to the battery-bank while charging the battery with po...

This paper presents in simple terms some models for reliability studies that become useful even in the absence of reliability data or when these data are scarce or lack confidence. In some cases, it is shown that the best decisions are independent of the reliability data values. In other cases, a risk analysis approach is recommended and the contribution of interval analysis and fuzzy set theory is highlighted.

ost of the Internet's infrastructure was designed to withstand physical failures-such as broken wires or computers-rather than attacks launched by legal network users. 1-3 The Internet's rapid growth, however, coupled with its cost-effective ability to move data across geographically dispersed heterogeneous information systems, has made it a virtual breeding ground for attackers. Furthermore, the improvisation and sophistication of hackers' attack strategies and methods have overshadowed progress in security systems development. A sustained attack on the Internet could cause a catastrophic infrastructure breakdown. According to a study on the Internet's structure, its reliance on a few key nodes makes it especially vulnerable to organized attacks by hackers and terrorists. 4 According to that report, if 1 percent of the key nodes were disabled, the Internet's average performance would be reduced by a factor of two; if 4 percent were shut down, the Internet's infrastructure would become fragmented and unusable. To make networked systems reliable and robust, we need vulnerability metrics that let us monitor, analyze, and quantify network and application behavior under a range of faults and attacks. Here, we present an agentbased framework for analyzing network vulnerability in real time. The framework lets us quantify how attacks and faults impact network performance and services, discover attack points, and examine how critical network components behave during an attack or system fault. Attack analysis In most network attacks, attackers overwhelm the target system with a continuous flood of traffic designed to consume all system resources (such as CPU cycles, memory, network bandwidth, and packet buffers). These attacks degrade service and can eventually lead to a complete shutdown. 5 There are two common types of attacks: • Server attacks. There are many types of server attacks, 6 including TCP SYN, Smurf IP, ICMP flood, and Ping of Death attacks. In some attacks, the attacker makes overwhelming connection requests to a victim server with spoofed source IP addresses. Due to TCP/IP protocol stack vulnerabilities, the victim server cannot complete the connection requests and wastes all of its system resources. As a result, the server cannot service legitimate traffic, which severely impacts network performance. • Routing attacks. Distributed denial-of-service (DDoS) attacks increasingly focus on routers. Once a router is compromised, it will forward traffic according to the attackers' intent. Similar to server attacks, the attackers aim to consume all router resources, forcing the router to drop all incoming packets, thus negatively affecting network performance and behavior. Analyzing vulnerability in networks and in Internet infrastructure still is in its infancy, and there's much room for improvement. Several existing tools, which are based on modeling network specifications, fault trees, graph models, and performance models, analyze vulnerability by checking logs of system software and monitoring performance metrics. 5,7 In what follows, we briefly high

Shuffle-exchange networks (SENs) have been widely considered as practical interconnection systems due to their size of its switching elements (SEs) and uncomplicated configuration. SEN is a network among a large class of topologically equivalent multistage interconnection networks (MINs) that includes omega, indirect binary n-cube, baseline, and generalized cube. In this paper, SEN with additional stages that provide more redundant paths are analyzed. A common network topology with a 2 Â 2 basic building block in a SEN and its variants in terms of extra-stages is investigated. As an illustration, three types of SENs are compared: SEN, SEN with an additional stage (SEN+), and SEN with two additional stages (SEN+2). Finally, three measures of reliability: terminal, broadcast, and network reliability for the three SEN systems are analyzed.

In this paper, we investigate a hybrid network coding technique to be used at a wireless base station (BS) or access point (AP) to increase the throughput efficiency of single-hop wireless networks. Traditionally, to provide reliability, lost packets from different flows (applications) are retransmitted separately, leading to inefficient use of wireless bandwidth. Using the proposed hybrid network coding approach, the BS encodes these lost packets, possibly from different flows together before broadcasting them to all wireless users. In this way, multiple wireless receivers can recover their lost packets simultaneously with a single transmission from the BS. Furthermore, simulations and theoretical analysis showed that when used in conjunction with an appropriate channel coding technique under typical channel conditions, this approach can increase the throughput efficiency up to 3.5 times over the Automatic Repeat reQuest (ARQ), and up to 1.5 times over the HARQ techniques.

This article, beyond presenting a spectrum of network reliability methods studied in the past decades, describes a scalable innovative ‘overlap technique’ to tackle large complex networks' reliability evaluation difficulties, which cannot be handled by straightforward reliability block diagramming (RBD) techniques used for the simple parallel‐series topologies. Examples are shown on how to apply the overlap algorithm to compute the ingress‐egress reliability. Monte Carlo simulations demonstrate the methods discussed. (1) Static (time independent), (2) dynamic (time dependent) using a versatile Weibull distribution to represent the multiple stages of network components from infancy to useful life period and to wear‐out, and (3) multistate versions to include derated behavior beyond conventional working and nonworking states, are illustrated for calculating the directional source‐target (s‐t) reliability of complex networks by using the Java software ERBDC: Exact Reliability Block...

Evolutionary computation algorithms are increasingly being used to solve optimization problems as they have many advantages over traditional optimization algorithms. In this paper we use evolutionary computation to study the trade-off between pleiotropy and redundancy in a client-server based network. Pleiotropy is a term used to describe components that perform multiple tasks, while redundancy refers to multiple components performing one same task. Pleiotropy reduces cost but lacks robustness, while redundancy increases network reliability but is more costly, as together, pleiotropy and redundancy build flexibility and robustness into systems. Therefore it is desirable to have a network that contains a balance between pleiotropy and redundancy. We explore how factors such as link failure probability, repair rates, and the size of the network influence the design choices that we explore using genetic algorithms.

This paper deals with asymptotic expressions of the Mean Time To Failure (MTTF) and higher moments for large, recursive, and non-repairable systems in the context of two-terminal reliability. Our aim is to extend the well-known results of the series and parallel cases. We first consider several exactly solvable configurations of iden- tical components with exponential failure-time distribution functions to illustrate

The exact calculation of network reliability in a probabilistic context has been a long-standing issue of practical importance, but a difficultone, even for planar graphs, with perfect nodes and with edges of identical reliability p. Many approaches (determination of bounds, sums of disjoint products algorithms, Monte Carlo evalu- ations, studies of the reliability polynomials, etc.) can only provide approximations when

The calculation of network reliability in a probabilistic context has long been an issue of practical and academic importance. Conventional approaches (determination of bounds, sums of disjoint products algorithms, Monte Carlo evaluations, studies of the reliability polynomials, etc.) only provide approximations when the network's size increases, even when nodes do not fail and all edges have the same reliability p. We consider here a directed, generic graph of arbitrary size mimicking real-life long-haul communication networks, and give the exact, analytical solution for the two-terminal reliability. This solution involves a product of transfer matrices, in which individual reliabilities of edges and nodes are taken into account. The special case of identical edge and node reliabilities (p and ρ, respectively) is addressed. We consider a case study based on a commonly-used configuration, and assess the influence of the edges being directed (or not) on various measures of network performance. While the two-terminal reliability, the failure frequency and the failure rate of the connection are quite similar, the locations of complex zeros of the two-terminal reliability polynomials exhibit strong differences, and various structure transitions at specific values of ρ. The present work could be extended to provide a catalog of exactly solvable networks in terms of reliability, which could be useful as building blocks for new and improved bounds, as well as benchmarks, in the general case.

We can analytically compute ETOP, which is not trivial, since ETOP is a noncommutative function of the link success probabilities. Although ETOP is a more involved metric, we show that the problem of computing paths with the minimum ETOP cost can be solved by a greedy algorithm. We will try to implement and evaluate a routing approach based on ETOP metric on wireless network.

A walk W in edge-colored graphs is called properly colored (PC) if every pair of consecutive edges in W is of different color. We introduce and study five types of PC acyclicity in edge-colored graphs such that graphs of PC acyclicity of type i is a proper superset of graphs of acyclicity of type i + 1, i = 1, 2, 3, 4. The first three types are equivalent to the absence of PC cycles, PC closed trails, and PC closed walks, respectively. While graphs of types 1, 2 and 3 can be recognized in polynomial time, the problem of recognizing graphs of type 4 is, somewhat surprisingly, NP-hard even for 2-edge-colored graphs (i.e., when only two colors are used). The same problem with respect to type 5 is polynomial-time solvable for all edge-colored graphs. Using the five types, we investigate the border between intractability and tractability for the problems of finding the maximum number of internally vertex-disjoint PC paths between two vertices and the minimum number of vertices to meet all PC paths between two vertices.

The leakage control is an important task, because it is associated with some problems such as economic loss, safety concerns, and environmental damages. The pervious methods which have already been devised for leakage detection are not only expensive and time consuming, but also have a low efficient. As a result, the global leakage detection methods such as leak detection based on simulation and calibration of the network have been considered recently. In this research, leak detection based on calibration in two hypothetical and a laboratorial networks is considered. Additionally a novel optimization method called step-by-step elimination method (SSEM) combining with a genetic algorithm (GA) is introduced to calibration and leakage detection in networks. This method step-by-step detects and eliminates the nodes that provide no contribution in leakage among uncertain parameters of calibration of a network. The proposed method initiates with an ordinary calibration for a studied network, follow by elimination of suspicious nodes among adjusted parameters, then, the network is re-calibrated. Finally the process is repeated until the numbers of unknown demands are equal to the desired numbers or the exact leakage locations and values are determined. These investigations illustrate the capability of this method for detecting the locations and sizes of leakages.

This paper presents a new approach to evaluating the health of composite generation and transmission systems. A wellbeing framework is used to classify the system states into healthy, marginal and at risk, according to a pre-defined deterministic criterion. In order to combine deterministic and probabilistic concepts, the proposed methodology uses a nonsequential Monte Carlo simulation, a multilevel nonaggregate Markov load model and new test functions to estimate the well-being indices. These test functions are based on an estimating process, designated as the one-step forward state transition, which is very flexible and efficient. Case studies on the IEEE-RTS (Reliability Test System) and on a modification of this system are presented and discussed.

Various criteria have been considered in the literature for selection of optimal sensor networks. Amongst these, maximization of network reliability is an important criterion. While there are several approaches for designing maximum reliability networks, uncertainty in the available sensor reliability data has not been considered in these designs. In this article we present two novel formulations that incorporate robustness to uncertainties in the reliability data. Towards this end the sensor network design problem for maximizing reliability is formulated as explicit-optimization (MINLP) problem using failure rates of sensors which have better scaling properties instead of sensor reliabilities. Constraint programming (CP) has been used for solving the resulting optimization problems. Use of CP also enables easy generation of pareto front characterizing trade-offs between performance, cost and robustness for various uncertainty scenarios. The utility of the proposed approach is demonstrated on a case study taken from the literature.

Various criteria have been considered in the literature for selection of optimal sensor networks. Amongst these, maximization of network reliability is an important criterion. While there are several approaches for designing maximum reliability networks, uncertainty in the available sensor reliability data has not been considered in these designs. In this article we present two novel formulations that incorporate robustness to uncertainties in the reliability data. Towards this end the sensor network design problem for maximizing reliability is formulated as explicit-optimization (MINLP) problem using failure rates of sensors which have better scaling properties instead of sensor reliabilities. Constraint programming (CP) has been used for solving the resulting optimization problems. Use of CP also enables easy generation of pareto front characterizing trade-offs between performance, cost and robustness for various uncertainty scenarios. The utility of the proposed approach is demonstrated on a case study taken from the literature.

This paper deals with the problem of finding a minimum-cost vertex subset S in an undirected network such that for each vertex v we can send d(v) units of flow from S to v. Although this problem is NP-hard in general, Tamura et al. have presented a greedy algorithm for solving the special case with uniform costs on the vertices. We give a simpler proof on the validity of the greedy algorithm using linear programming duality and improve the running time bound from O(n 2 M) to O(nM), where n is the number of vertices in the network and M denotes the time for max-flow computation in the network with n vertices and m edges. We also present an O(n(m + n log n)) time algorithm for the special case with uniform demands and arbitrary costs.

The authors define the probability of receiving correct decisions from all the clusters by the data fusion centre as the reliability of distributed detection in clustered wireless sensor networks and formulate it in two cases of parallel and serial distributed detection. An energy-efficient distributed detection method-called hybrid distributed detection-is also proposed in which distributed detection is performed during hop-by-hop transmission of data from the cluster nodes to the cluster head. It is shown that this method conserves much more energy than previously proposed methods and results in considerable improvement in network reliability.

The purpose of adding redundancy to unique path MINs is to increase their reliability. In this paper, a fault-tolerant multistage interconnection network (MIN), a 2-dilated baseline network is analyzed for reliability and performance improvements. The new proposed MIN (FTELMIN) has all the available paths established between an input terminal and an output terminal in such a way that they never pass through an identical switching element (SE) in the next stage. The loads on SEs, therefore, are shared efficiently. This MIN provides 2 n paths between any pair of source and destination where n is the number of stages in the MIN. Extra links added to enhance the performance never complicate the routing scheme. The MTTF is being used as the measure of reliability and it has been observed that FTELMIN is more reliable as compared to 2-dilated ELMIN.

The load shaping technique is an important key that has been widely implemented inelectrical power systems. The benefits of this activity involve system reliability enhancement and operation requirement satisfaction. In this study, the benefits of load shaping are investigated based on reliability impact. First, the reliability indices have been assessed with no original load. Secondly, the same indices are assessed when load shaping is considered. Results show that the proposed model yields higher accurate reliability assessment and, therefore, a more robust strategy to be implemented. Monte Carlo simulation is utilized to calculate predicted energy not supplied.The paper demonstrates IEEE reliability test system. It describes a comparison of reliability of generating systems based on real time assessment.

This paper presents the results of a survey aimed at understanding the status of Internet measurement platforms usage, deployment and capabilities in Africa. It presents findings related to prevalence of measurement in the region, the reasons why the different business categories investigated conduct Internet measurement as well as the metrics of interest to these entities. The survey also looked at the popular measurement platforms that the respondents use in their measurement activities as well as the platforms that are hosted by businesses and users in the African region. The survey also recorded responses related to data handling and privacy considerations. A total of 123 responses were received from 34 countries. The survey revealed that Internet measurements are not widely conducted in the region largely due to the inadequacy of deployed measurement platforms, the lack of awareness in the subject, and the lack of relevant skills to carry out the measurement tasks. We outlined some recommendations to remedy these issues.

Reliability optimization, number of spanning trees, most vital edges, matrix operation Reader Aids-General purpose: Sensitivity analysis of network reliability Special math needed for derivations: Matrix operations, graph Special math needed to use results: Same Results useful to: Reliability analysts, network designers theory, and associated jargon Summary & Conclusions-A most vital edge of a graph (w.r.t. the spanning trees) is an edge whose deletion most drastically decreases the number of spanning trees. We present an algorithm for determining the most vital edges based on Kirchoff's matrixtree theorem whose asymptotic time-complexity can be reduced to that of the fastest matrix multiplication routine, currently O(n2."$. The foundation for this approach is a more general algorithm for directed graphs for counting the rooted spanning arborescences containing each of the arcs of a digraph. A network can be modeled as a probabilistic graph. Under one such model proposed by Kel'mans, the all-terminal network reliability, maximizing the number of spanning trees is critical to maximizing reliability when edges are very unreliable. For this model, the most vital edges characterize the locations where an improvement of the reliability of the link most improves the reliability of the network.

To improve the resilience of critical infrastructure systems, their intrinsic properties need to be understood and their resilience state needs be identified. In the literature, several methods to evaluate networks' reliability and resilience can be found. However, the applicability of these methods is usually restricted to small-size networks. In this paper, the transportation network of a large-scale virtual city is considered as a case study. A random removal of the roads is applied simulating the network's failure. The network reliability is then calculated using the Destruction Spectrum (D-spectrum) method and a Monte Carlo approach has been developed to generate failure permutations that are necessary for the evaluation of the D-spectrum se. In addition, the Birnbaum Importance Measure (BIM) has been adopted in this study to determine the importance of the network's components. The methodology adopted in this study can be also extended to all network-based systems. The paper also introduces resilience indicators as a soft tool to predict the performance and serviceability of transportation networks.

1 INTRODUCTION HIS Traditional system-reliability measures include reliability, availability, and interval availability. Re-liability is the probability that a system operates without interruption during an interval of interest under specified conditions. Reliability can be extended to in- ...

Performance reliability of road networks has become a more prevailing concern for engineers and planners involved in network design. To improve network reliability the most, engineers and planners may need to decide which links need improvement and at the same time account for the route choice behavior of network users. Using a simple network example, a new reliability version of Braess’s paradox is presented showing that increasing the capacity or decreasing the variability of travel time for some links may actually lead to a less reliable network. A bilevel programming model is proposed through which the reliability paradox can be avoided and an optimal improvement scheme for the existing links may be determined to achieve the most reliable network, subject to a budget constraint. Finally, a numerical example is presented to illustrate the model together with a sensitivity analysis–based algorithm.

Introduction Reliability context Basic model 2 Crude Monte Carlo simulation Crude estimator Rarity and associated problems 3 Recursive Variance Reduction (RVR) algorithm Description Relative error analysis 4 Balanced RVR Description Relative error analysis 5 Zero-variance Approximation RVR 6 Numerical results 7 Conclusions B. Tuffin et al.