A novel fault management approach for DWDM optical networks

Connection availability is considered as a critical metric when providing differentiated services in Wavelength‐Division Multiplexing mesh networks. Indeed, one of the major concerns of optical network operators is related to improving the availability of services provided to their highest‐class clients. Achieving this objective is possible through managing faults using the different classical protection schemes, namely the so‐called dedicated and shared protection schemes. However, the majority of the work concerning protection schemes has considered the primary connections as equally important when contending for the use of the backup resources. As a main contribution in this paper, we therefore propose an improvement of the existing protection schemes through the introduction of relative priorities among the different primary connections contending for the access to the protection path. To evaluate numerically the benefits of the service differentiation feature introduced in our proposal, we first develop a mathematical model, based on which we derive explicit expressions for the average connection availabilities that result from both the classical protection schemes and the proposed priority‐aware one. Through this model, we show how the availability of the highest‐class clients is improved when deploying the proposed priority‐aware protection scheme. Finally, with the same objective in mind, we develop a simulation study, where a given set of connection demands with predefined availability requirements is provisioned using different protection strategies. Through this study, we show that the priority‐aware protection strategy satisfies service‐availability requirements in a cost‐effective manner compared with the classical protection schemes.Copyright © 2006 John Wiley & Sons, Ltd.     

Availability-Aware Provisioning Strategies for Differentiated Protection Services in Wavelength-Convertible WDM Mesh Networks

In an optical WDM mesh network, different protection schemes (such as dedicated or shared protection) can be used to improve the service availability against network failures. However, in order to satisfy a connections service-availability requirement in a cost-effective and resource-efficient manner, we need a systematic mechanism to select a proper protection scheme for each connection request while provisioning the connection. In this paper, we propose to use connection availability as a metric to provide differentiated protection services in a wavelength-convertible WDM mesh network. We develop a mathematical model to analyze the availabilities of connections with different protection modes (i.e., unprotected, dedicated protected, or shared protected). In the shared-protection case, we investigate how a connection's availability is affected by backup resource sharing. The sharing might cause backup resource contention between several connections when multiple simultaneous (or overlapping) failures occur in the network. Using a continuous-time Markov model, we derive the conditional probability for a connection to acquire backup resources in the presence of backup resource contention. Through this model, we show how the availability of a shared-protected connection can be quantitatively computed. Based on the analytical model, we develop provisioning strategies for a given set of connection demands in which an appropriate, possibly different, level of protection is provided to each connection according to its predefined availability requirement, e.g., 0.999, 0.997. We propose integer linear programming (ILP) and heuristic approaches to provision the connections cost effectively while satisfying the connections' availability requirements. The effectiveness of our provisioning approaches is demonstrated through numerical examples. The proposed provisioning strategies inherently facilitate the service differentiation in optical WDM mesh networks.     

Probability analysis of a 2-out-of-n: F system with common cause failure, multiple failure and dependent failure

We analyze 2-out-of-n:F system with Common Cause Failure (CCF), Multiple Failure (MF) and Dependent Failure(DF) by using the method of extended Markov state transition and 2-dimensional Laplace transition method. Computing the system availability, we studied the effect of repair in the CCF, MF and DF environment. we introduced the new steady state availability by using the results of the Laplace transformed availability. We apply basic relation of 2-dimensional Laplace transformation for the new availability analysis. Then we apply this transformation at different differential equations. The result of this analysis is to get the fixed quantity of system availability according to the repair rate change     

Availability-aware service provisioning in SD-EON-based inter-datacenter networks

The tremendous transmission capacity and flexible spectrum allocation scheme make elastic optical networks (EONs) one of the most promising infrastructures for constructing the interconnection in datacenter (DC) networks. Meanwhile, as DC traffics exhibit highly dynamic and heterogeneous features, differentiated service provisioning schemes are desired. In this paper, we take the advantage of centralized network control and management provided by the software-defined elastic optical networks (SD-EONs) and investigate availability-aware service provisioning in SD-EON-based inter-datacenter (inter-DC) networks. We first describe the problem of availability-aware service provisioning in SD-EON-based inter-DC networks and present the theoretical analysis for service availability. Then, we propose an availability-aware service provisioning algorithm (ASP) that leverages different path protection schemes to satisfy different service availability requirements. A service downgrading (SD) strategy is also designed as a supplement of ASP to further improve its performance. Simulation results show that the proposed ASP-SD algorithm can effectively improve the spectrum efficiency without sacrificing availability.     

Optical multicast provisioning with differentiated leaf availability guarantee in WDM networks

As multicast applications become more and more popular, implementing multicast in the optical domain has attracted increased attention due to its more efficient bandwidth usage. And also these services have quality-of-service requirements. In this article, the problem of cost-effective optical multicast provisioning to satisfy the differentiated leaf availability requirements is formally stated. A Mixed Integer Linear Program formulation is proposed for provisioning dedicated light-tree protection with differentiated leaf availability guarantee. The algorithm is so complex and infeasible that we also propose a feasible two-step approximate approach to solve the problem. Different from the previous schemes, our scheme finds out the primary light-trees and backup paths for destination nodes whose availability is not satisfied. Because of taking the different leaf availability requirements into account, the proposed algorithm obtains a more efficient feasible solution requiring less network resources.     

A generic model of equipment availability under imperfect maintenance

This paper explores the impact of imperfect repair on the availability of repairable equipment. Kijima's first virtual age model is used to describe the imperfect repair process. Due to the complexity of the underlying assumptions of this model, we are unable to derive a closed-form equation for availability. Therefore, simulation modeling & analysis are used to evaluate equipment availability. Based on initial availability plots, a generic availability function is proposed. A 2/sup 3/ factorial experiment is performed to evaluate the accuracy of this model. The maximum absolute error between the simulation output, and the corresponding values of the availability function is 3.82%. This indicates that our proposed function provides a reasonable approximation of equipment availability, which simplifies meaningful analysis for the unit. Therefore, a method is defined for determining optimum equipment replacement intervals based on average cost. Next, meta-models are developed to convert equipment reliability & maintainability parameters into the coefficients of the availability model. We expand on our initial experiment using a circumscribed central composite experimental design. We evaluate the accuracy of the meta-models for the 15 experiments & 50 random experiments within the design space. For the 50 new experiments, we compare the replacement policy obtained from analysis of the meta-model to the policy obtained directly from the simulation output. The average increase in cost resulting from the sub-optimal replacement policy is only 0.10%. Therefore, we conclude that the meta-models are robust, and provide good estimates of the parameters of our proposed availability function. By doing this, we eliminate the need to perform simulation to obtain the parameters of the availability model.     

Upgrading service availability of optical networks: A labor force perspective

Service availability is an important issue in optical networks. Much research attention has been drawn to the provisioning of reliable connections achieved by approaches such as routing and wavelength assignment and by protection and restoration mechanisms. In contrast, the research on upgrading networks to meet new or dynamic demands of service availability based on network upgrading process has been comparatively lacking. In this paper, we address this issue by upgrading service availability from the perspective of labor forces for network maintenance. Our approach is premised on the assumption that the time period for fixing an optical link can be reduced by using more network resources of labor forces. To model this concept, we conduct Amdahl's law, a well‐known theorem in parallel computing, to describe human teamwork. To show the effectiveness of this concept, we propose mixed integer linear programming aiming at either maximizing service availability under limited labor forces or minimizing labor forces for predetermined service availability. In addition, a heuristic algorithm for upgrading service availability is presented. Our experimental results show that our network upgrading process can improve service availability optimally with a fixed number of forces and the proposed heuristic algorithm can effectively save computation time.     

Blocking probability in a limited-availability group carrying mixture of different multichannel traffic streams

In this paper we propose an approximate, recurrent method of calculations of the blocking probability and of the distribution of being busy in limited- availability groups to which the mixture of different multichannel traffic streams is offered. The method is based on introducing the relevant combinatorically- determined conditional probabilities of passages between adjacent states of the group into the equations determining the distribution of busy channels in a full- availability group. The result of analytical calculations of the blocking probability are compared with the results of digital simulation of limited- availability groups. The proposed method can be used in analysis of isdn and b-isdn networks and systems.     

The Availability of a k-out-of-n:G Network

A method is described for calculating the analytic availability of a k-out-of-n:G network where the availability of each component may be different. An algorithm and a FORTRAN subroutine are provided to calculate this type of availability.     

Availability analysis under multiple link failures in WDM networks with shared-link connections

In optical Wavelength Division Multiplexing (WDM) networks, different protection schemes have been proposed in the literature, namely, dedicated protection and shared protection. Shared protection techniques significantly reduce the required spare capacity by providing the same level of availability as dedicated protection. However, current mission critical applications (which heavily depend on the availability of communication resources) require connection availability in the order of 99.999% or higher, which corresponds to a downtime of almost 5 min a year on the average. Therefore, in order to satisfy a connection serviceavailability requirement defined by the users Service Level Agreement in a cost-effective and resource-efficient way, network operators need a systematic mechanism to evaluate the network availability under multiple failure scenario to ensure that current network configuration can meet the required availability degree; otherwise, a network upgrade is required. Unfortunately, under multiple failure scenario, traditional availability analysis techniques based on reliability block diagrams are not suitable for survivable networks with shared spare capacity. Therefore, a new concept is proposed to facilitate the calculations of network availability. In this paper, we propose an analytical model for evaluating the availability of a WDM network with shared-link connections under multiple link failures. The analytical model is also verified using Monte Carlo simulation. The proposed model significantly contributes to the related areas by providing network operators with a quantitative tool to evaluate the system availability and, thus, the expected survivability degree of WDM optical networks with shared connections under multiple link failures.     

Repairable single server systems with multiple breakdown modes

Typically the availability, steady-state queue length distribution, and mean queue length of Markov queueing systems subject to random breakdowns are computed by generating function or matrix geometric numerical methods. In this paper we point out that, for single server systems, a simple partition balance approach is easier. We illustrate this observation by deriving expressions for the availability, steady-state queue length distribution, mean queue length, and server utilization of a single server system subject to multi-mode, bi-level, Poisson distributed breakdowns of exponentially distributed duration. A numerical example illustrating some of the relations between these measures is also given. Our setup provides a simple, computationally tractable, Markov model for systems in which breakdowns of different types occur and are repaired at rates dependent on the type and severity of the breakdown.     

使用可用度分配模型研究

使用可用性是某些复杂系统战备完好性的重要参数。将复杂系统按组成结构分成若干分系统,重点提出重要程度因素,并构建了重要度相同和不同的两种使用可用度模型,最后给出了混联系统的使用可用度分配模型及其求解方法。     

Shadowing correlation assessment and modeling for satellite diversity in urban environments

Non‐geostationary orbit satellite networks have dynamic, yet deterministic topologies. This paper deals with the consequences of relying on the use of multiple visible satellites to improve availability with time/locations through satellite diversity techniques. The assumption of independent blockage events in two different satellite‐to‐mobile links is generally not accurate and information on shadowing correlation should be taken into account in the assessment of availability.In this paper a shadowing correlation study for urban environments is presented and a model for the real environments, as well as for a generic urban environment is inferred. The model proposed here is simple and can be run on a computer. It also relates urban and constellation geometries thus allowing the identification of those cases for which satellite diversity gain should be expected. As a result of this analysis and modelling, we present empirical analytical expressions describing positive correlation coefficient as a function of satellite angular separation (azimuth and elevation). We also show that an angle exists above which correlation can be negative and satellite diversity can sensibly improve link availability. Copyright © 2002 John Wiley & Sons, Ltd.     

可修复网络稳态可用度分析

本文提出了可修复网络稳态可用度的数学分析方法。通过证明得出不可修复网络的可靠性多项式适用于可修复网络的可用度，只需相应地把部件的可靠度改为部件的可用度，把部件的不可靠度改为部件的不可用度     

A new model for fault and availability in complex multimedia services

The definition of fault and availability in systems that offer simple services tends to be binary and static. This is because 1) systems that offer simple services are operative if and only if all the parts of the system are in full operative condition and 2) faults can be defined by the service providers regardless of the context in which the service is used. In the case of complex multimedia services however, even when parts of the system are not available, the service is still worth offering. Moreover, the definition of the level of failure at which the service should be declared as unavailable is user and context dependent. In this paper we introduce a new way of defining fault and availability that is appropriate for systems that offer not only simple but also complex multimedia communication services. Our model provides ways of capturing in a useful way 1) the difference between functionally identical faults that appear in different applications, 2) the difference between faults that although they are functionally identical, they have different roles and significance in the application, 3) the change in the value of providing certain resources, depending on the availability of other resources, 4) the difference in the value of providing certain resources depending on the preferences of the users. Our model takes into consideration the user's point of view as far as availability and fault tolerance are concerned. It also provides different degrees of fault and availability (as opposed to binary definition of faults). We use these definitions to allocate the available resources to support the different parts of the system in a provably optimal way, i.e., in a way that maximizes the expected value of the offered service. This revised version was published online in June 2006 with corrections to the Cover Date.     

Dynamic channel partitioning with flexible channel combination for TDMA-based cellular systems

In this paper, we propose flexible dynamic channel partitioning (FDCP) with a flexible channel-combination scheme to support multiple services. CP is based on the idea that different services may require different signal-to-interference ratios (SIRs), and thus, different reuse factors. In FDCP, different services are allocated to the channels depending on the reuse factors they require. FDCP tries to minimize the effect of the assigned channels on the channel availability to the interfering cells and to reduce the overall reuse distances of the systems.     

Availability Evaluation of Ground-to-Air Hybrid FSO/RF Links

Recently, a hybrid architecture that utilizes the complementary nature of free-space optics (FSO) and radio frequency (RF) links with respect to their individual weather sensitivities was proposed to significantly increase availability for terrestrial broadband links. Based on this architecture, we developed a channel model integrating both the RF and FSO channels. Using the model and cloud distribution data obtained from the International Satellite Cloud Climatology Project, availability of an airborne hybrid FSO/RF link is evaluated. From the results, we conclude that if the FSO link alone is used, availability is greatly hampered by clouds due to attenuation and temporal dispersion. Contrarily, the RF signals are relatively immune to cloud influence, thus improving the hybrid link availability significantly. Furthermore, because of the significant temporal dispersion caused by multiple scattering of cloud particles, availability of FSO links can be improved by using frequency division schemes, though far from compensating for losses incurred by clouds.     

Comparison of the usability and security of NFC’s different operating modes in mobile devices

This paper highlights the benefits and drawbacks of NFC’s different operating modes with regard to their usability and security. Based on an analysis of both traditional and new communication concepts for mobile NFC devices, their current availability and, specifically, the features to provide security are evaluated. The result of this evaluation is a comparison between the availability, the usability and the security of NFC’s different operating modes.     

The impact of stochastic resource availability on cognitive network performance: modeling and analysis

Cognitive radio networks emerge as a promising solution for overcoming shortage and inefficient use of bandwidth resources by allowing secondary users (SUs) to access the primary users' (PUs) channel so long as they do not interfere with them. The dynamical spectrum availability makes SU's packet average delay one of the most important performance measures of a cognitive network. It is important to understand the nature of delay, as well as its dependence on PU behaviors. In this paper, we analytically model and analyze the dynamics of the spectrum availability and their impact on the SU's packet delay. The cognitive network is modeled as a discrete‐time queueing system. PU channel occupancy is modeled as a two‐state Markov chain. Our contribution in this paper is defining and characterizing the properties of the random process that describes the availability of the opportunistic resources. In addition, we apply the mean residual service time concept to achieve an analytical solution for the queueing delay. Moreover, inspired by the slotted Aloha system, we model the packet service mechanism and determine the manner in which it depends on the resource availability. The delay becomes unbounded if the spectrum availability dynamics are not carefully considered in network design. Copyright © 2015 John Wiley & Sons, Ltd.     

A Scalable Path Protection Mechanism for Guaranteed Network Reliability Under Multiple Failures

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