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Energy-Efficient Design of Survivable WDM Networks with Shared Backup

In recent years, energy-efficient design of optical WDM networks has become increasingly important as efforts to reduce the operational expenditure (Opex) and the carbon footprint of the internet are prioritized. In this paper we focus on energy- efficient survivable network design where backup resources are shared for efficient capacity consumption. However there is a trade-off between energy-efficiency and survivability. Survivable network design strategies lead to lightly loaded links in order to minimize the risk in case of a failure and to increase the shareability of backup resources. On the contrary, energy-efficient network design strategies tend to increase the load in a set of links as a consequence of concentrating the traffic in order to be able to switch off as much network resources as possible. In this study, we present a novel method to simultaneously minimize Capex and Opex while providing an energy-efficient, shared backup protected network, under the assumption of backup capacity in sleep mode. For the first time we propose an ILP formulation for the energy-efficient shared backup protection problem. By exploiting the sleep mode for the backup resources, we observe that the ILP solution of our mathematical model brings up to 40% gain in energy efficiency in comparison to energy-unaware shared backup protection approach.

An Empirical Study on Object-Oriented Metrics and Software Evolution in Order to Reduce Testing Costs by Predicting Change-Prone Classes

Software maintenance cost is typically more than fifty percent of the cost of the total software life cycle and software testing plays a critical role in reducing it. Determining the critical parts of a software system is an important issue, because they are the best place to start testing in order to reduce cost and duration of tests. Software quality is an important key factor to determine critical parts since high quality parts of software are less error prone and easy to maintain. As object oriented software metrics give important evidence about design quality, they can help software engineers to choose critical parts, which should be tested firstly and intensely. In this paper, we present an empirical study about the relation between object oriented metrics and changes in software. In order to obtain the results, we analyze modifications in software across the historical sequence of open source projects. Empirical results of the study indicate that the low level quality parts of a software change frequently during the development and management process. Using this relation we propose a method that can be used to estimate change-prone classes and to determine parts which should be tested first and more deeply.

Shared-Path Protection With Delay Tolerance (SDT) in Optical WDM Mesh Networks

Optical wavelength-division-multiplexing (WDM) networks have emerged as an ideal backbone for the dynamic transport of bandwidth-intensive applications. Most emerging applications require end-to-end survivable connections to be set up for specific time durations that have sliding or fixed setup times (such as IPTV, grid computing backup storage). It is critical for the development of future network infrastructure that user-centric, dynamic, and end-to-end management and control mechanisms are devised to bridge the gap between the transport capacity and the needs of new applications at the customer edges. In this paper, we study the problem of dynamic provisioning of user-controlled connection requests that have specified holding times and delay tolerances. Delay tolerance is a measure of customer patience, and it is defined as the duration a connection request can be held until it is set up. A connection that cannot be established at the instant of its request could potentially be set up in the remaining duration of its delay tolerance. In this study, different dynamic scheduling algorithms are developed and compared by giving priority to connections according to their arrival rates, delay tolerances, and holding times. Using a mathematical model for impatient requests and simulation experiments, we show that delay tolerance flexibility in the traffic model provides a reduction of up to 50% on blocking probability, without the use of extra backup capacity.

Dynamic Scheduling of Survivable Connections with Delay Tolerance in WDM Networks

In optical wavelength-division multiplexing (WDM) networks, recent technological progress is enabling dynamic optical transport in which leasable circuits (connections) can be set up and released for a specific duration of time, providing large capacity to bandwidth-hungry applications. Set-up times can be flexible or fixed, depending on the type of the application. Since the interruption of a high-speed optical connection could lead to huge loss of data, such connections need to be protected against failures. We study the problem of dynamic provisioning of user-controlled connection requests that have specified holding times and particular delay tolerances with shared path protection. The metric of delay tolerance is a measure of customer patience, and it is defined as the time a connection request can be held until it is set up. A connection that cannot be established at the instant of its request could potentially be set up in the remaining duration of its delay tolerance. We show that a reduction of up to 50 percent can be achieved on blocking probability by exploiting delay tolerance in networks without using extra backup capacity. In this study we explore different queuing policies for impatient customers. Different dynamic scheduling algorithms are applied and compared by giving priority to connections according to their arrival rates, delay tolerances and holding times alternatively.

A UML profile for role-based access control

When building an access control aware system, integrating access control specifications into the development process is problematic. Even if security modeling is structured at the early phases of development, security mechanisms are placed into the system at the final phases. This late integration affects security and maintainability of the resulting system in a bad way. In this paper, we present a solution for this problem. We propose a Unified Modeling Language (UML) Profile for Role-Based Access Control (RBAC), with which access control specifications can be modeled graphically together with problem domain specifications from the beginning of the design phase, making it possible to extend security integration over entire development process. We employed significant RBAC constraints like static and dynamic separation of duties into the profile and introduced how Object Constraint Language (OCL) is used to validate well-formedness and meaning of information models against the RBAC.

Availability-guaranteed connection provisioning with delay tolerance in optical WDM mesh networks

We propose a novel dynamic provisioning scheme exploiting a new user-centric SLA metric, called delay tolerance, in availability-guaranteed shared-path-protected optical WDM networks. Significant reduction in blocking probability is achieved without sacrificing additional resources.

Object Oriented Software Clustering Based on Community Structure

Software comprehension plays a critical role in software maintenance. Understanding a software system is not an easy task because in most cases documentation of software design is outdated, incomplete or absent. Therefore support of tools and algorithms are necessary for software developers to understand software quicker and easier. Clustering algorithms have been widely used for software architecture recovery. Their performance depends not only on the algorithm itself but also on the nature of the software system. For example, an algorithm that is successful for a procedural program or a small software system or might be unsuccessful for a large system developed in object-oriented paradigm. In this paper, we propose the adaption of the fast community detection algorithm for object-oriented software clustering and evaluate its performance with other clustering algorithms in the literature. It is an agglomerative hierarchical clustering algorithm that has been introduced to find communities in networks. The algorithm can operate on directed weighted graphs and it has a considerable speed advantage over other algorithms. Experimental results show that the algorithm also performs well for clustering object-oriented systems.

An efficient and adaptive channel handover procedure for cognitive radio networks

In designing cognitive radio systems, one of the most critical issues is handling the channel handover process CHP. The CHP consists of spectrum sensing, spectrum decision, negotiation on the common control channel, and adjustment of frequency and modulation settings, and such, it can be a time-consuming process. Consequently, initiating the CHP after each detected user activity UA can decrease the aggregate spectrum utilization. To alleviate this problem, we introduce a novel handover strategy to find the optimal trade-off between the durations of the CHP and UAs. With the use this model, secondary users SUs track only local information on their current data channel to make the decision to initiate the CHP or to wait for the termination of the ongoing UA. The system adapts to the dynamic conditions of the data channels and reduces the frequency of handovers to increase throughput and decrease access delay. We give analytical utilization bounds for SUs and also compare the performance of our model to those of other channel handover strategies by using extensive simulations. Our results for channels with heterogeneous loads and dynamic environments show that this model can clearly decrease the frequency of handover and consequently increase the aggregate SU utilization. Copyright

A learning-based module extraction method for object-oriented systems

We propose a novel learning-based module extraction approach for OO systems.The approach is based on common OO design characteristics and design principles.We train our model with data obtained from a real modular reference-system.Experimental results show that it outperforms existing methods for OO systems.Extracting modules can help in software comprehension and architecture recovery. Developers apply object-oriented (OO) design principles to produce modular, reusable software. Therefore, service-specific groups of related software classes called modules arise in OO systems. Extracting the modules is critical for better software comprehension, efficient architecture recovery, determination of service candidates to migrate legacy software to a service-oriented architecture, and transportation of such services to cloud-based distributed systems. In this study, we propose a novel approach to automatic module extraction to identify services in OO software systems. In our approach, first we create a weighted and directed graph of the software system in which vertices and edges represent the classes and their relations, respectively. Then, we apply a clustering algorithm over the graph to extract the modules. We calculate the weight of an edge by considering its probability of being within a module or between modules. To estimate these positional probabilities, we propose a machine-learning-based classification system that we train with data gathered from a real-world OO reference system. We have implemented an automatic module extraction tool and evaluated the proposed approach on several open-source and industrial projects. The experimental results show that the proposed approach generates highly accurate decompositions that are close to authoritative module structures and outperforms existing methods.

A novel channel handover strategy to improve the throughput in cognitive radio networks

Cognitive radio (CR) is the most promising solution to spectrum scarcity and spectrum underutilization problems. Most of the research in CR design ignores the cost of channel handover process (CHP) in cognition cycle. However, CHP can be a time consuming process that consists of spectrum sensing, spectrum decision, negotiation through control channel, and adjustment of frequency and modulation settings. Taking all of these steps into account, we deduce that the frequency of CHP is one of the most critical CR design issues. In this sense, initiating the CHP after detecting each primary user (PU) activity can decrease the aggregated spectrum utilization. In this paper, we analyze the trade-off between initiating a CHP to find an idle channel and staying in the current data channel for a while to catch free slots when some PU activity is detected. We propose a novel channel handover strategy (CHS) to balance this trade-off. In this CHS, secondary users (SUs) track only their current data channel and do not need information about the whole spectrum environment to determine whether to start CHP or not. Simulation results show that the proposed CHS can clearly decrease the frequency of handovers and increase the aggregated SU utilization.