Failure Recovery

In this paper, we consider IP fast recovery from single-link failures in a given network topology. The basic idea is to replace some existing routers with a designated switch. When a link fails, the affected router will send all the affected traffic to the designated switch (through pre-configured IP tunnels), which will deliver the affected traffic to its destination without using the failed link. The goal of the approach is to achieve faster failure recovery than traditional routing protocols that employ reactive computing upon link failures. Software-Defined Networking (SDN) switches can serve as the designated switches because they can flexibly redirect affected traffic to other routes, instead of only to the shortest paths in the network. However, SDN switches are very expensive. Our objective is to minimize the number of SDN switches needed and to guarantee that the network can still recover from any single-link failure. For networks with uniform link costs, we show that using normal non-SDN switches with IP tunneling capability as designated switches can guarantee recovery from any single-link failure. For networks with general link costs, we show that by using SDN switches only when necessary, we can reduce the total number of SDN switches needed compared to an existing work.

Overbooking represents an important strategy for many service providers that apply revenue management. Although the objective is to overbook such that no customers are denied service, denials may result when the customer no-show rate is lower than expected. Research has shown that denied service can increase customer complaining behavior, and decrease customer satisfaction and spending behavior. Therefore, it behooves the service provider to put a service recovery strategy in place that will minimize the likelihood of these negative outcomes. This study investigates, in the context of denied service due to hotel overbooking, the role of overcompensation (type and amount) in shaping customers’ reactions to the service failure/recovery experience. Results suggest that cash-based overcompensation will yield significantly higher satisfaction ratings than voucher-based overcompensation or normal compensation alone, although the relationship between cash-based overcompensation and satisfa...

In this paper a distributed routing management solution is described that takes into consideration statistical Quality of Service (QoS) information about the state of network links. The goal is to offer dynamic metrics to the routing algorithm based on the current resource utilization, i.e. the routing metrics will depend on the traffic load and the delay measured on individual links in real-time. Identification of congested areas allows situation-aware path selection, enhancing the global capacity of the network by determining optimal routes. Streszczenie. W artykule przedstawiono sposób zarz dzania routowaniem, w którym wzi to pod uwag parameter QoS na temat stanu linków w sieci. G ównym celem by o zastosowanie dynamicznej metryki do algorytmu routowania, opartej na informacji o bie cym wykorzystaniu zasobów. Identyfikacja rejonów przeci enia pozwala na polepszenie dzia ania i pojemno ci sieci poprzez optymalizacj cie ki routowania. (Kontrola przeci enia w routowaniu QoS).

Abstract—This paper presents the design principles and the practical implementation of a routing management solution which takes into account statistical cross-layer Quality of Service information regarding the state of the network. Link monitoring and ...

We design a peer-to-peer technique called ZIGZAG for single-source media streaming. ZIGZAG allows the media server to distribute content to many clients by organizing them into an appropriate tree rooted at the server. This applicationlayer multicast tree has a height logarithmic with the number of clients and a node degree bounded by a constant. This helps reduce the number of processing hops on the delivery path to a client while avoiding network bottleneck. Consequently, the end-to-end delay is kept small. Although one could build a tree satisfying such properties easily, an efficient control protocol between the nodes must be in place to maintain the tree under the effects of network dynamics and unpredictable client behaviors. ZIGZAG handles such situations gracefully requiring a constant amortized control overhead. Especially, failure recovery can be done regionally with little impact on the existing clients and mostly no burden on the server.

Given the fact that the current Internet does not widely support IP Multicast while content-distribution-networks technologies are costly, the concept of peer-to-peer could be a promising start for enabling large-scale streaming systems. In our so-called Zigzag approach, we propose a method for clustering peers into a hierarchy called the administrative organization for easy management, and a method for building the multicast tree atop this hierarchy for efficient content transmission. In Zigzag, the multicast tree has a height logarithmic with the number of clients, and a node degree bounded by a constant. This helps reduce the number of processing hops on the delivery path to a client while avoiding network bottleneck. Consequently, the end-to-end delay is kept small. Although one could build a tree satisfying such properties easily, an efficient control protocol between the nodes must be in place to maintain the tree under the effects of network dynamics. Zigzag handles such situations gracefully requiring a constant amortized worst-case control overhead. Especially, failure recovery is done regionally with impact on at most a constant number of existing clients and with mostly no burden on the server.

We describe a new scalable application-layer multicast protocol, specifically designed for low-bandwidth, data streaming applications with large receiver sets. Our scheme is based upon a hierarchical clustering of the application-layer multicast peers and can support a number of different data delivery trees with desirable properties.We present extensive simulations of both our protocol and the Narada application-layer multicast protocol over Internet-like topologies. Our results show that for groups of size 32 or more, our protocol has lower link stress (by about 25%), improved or similar end-to-end latencies and similar failure recovery properties. More importantly, it is able to achieve these results by using orders of magnitude lower control traffic.Finally, we present results from our wide-area testbed in which we experimented with 32-100 member groups distributed over 8 different sites. In our experiments, average group members established and maintained low-latency paths and ...

This paper presents OntoOmnia, a new meta-operating system architecture designed to address the challenges and risks of AI singularity. While previous research has focused on embedding ethical principles or ontological frameworks into AI systems, OntoOmnia takes a significant step further by introducing resilience, automated failure recovery, and participatory governance as core architectural elements.

Building on the OntoLoop/Omnia lineage, OntoOmnia integrates a recursive ethical kernel, distributed consensus mechanisms, and the innovative “Phoenix Loop” process. These features allow both agents and the system itself to transparently record, recover, and evolve in the face of catastrophic failure, emergent misalignment, or existential threats.

In contrast to earlier works that emphasized philosophical structure or agent-level ethics, this study explicitly targets the meta-governance of superintelligent agents and singularity-scale risks. OntoOmnia offers a conceptual but actionable blueprint for constructing self-healing, ethically-aligned, and collectively governed AI infrastructures, contributing a fresh paradigm for AI safety and future digital societies.

The concept of state and its applications vary widely across big data processing systems. This is evident in both the research literature and existing systems, such as Apache Flink, Apache Heron, Apache Samza, Apache Spark, and Apache Storm. Given the pivotal role that state management plays, particularly, for iterative batch and stream processing, in this survey, we present examples of state as an enabler, discuss the alternative approaches used to handle and implement state, capture the many facets of state management, and highlight new research directions. Our aim is to provide insight into disparate state management techniques, motivate others to pursue research in this area, and draw attention to open problems.

The concept of state and its applications vary widely across big data processing systems. This is evident in both the research literature and existing systems, such as Apache Flink, Apache Heron, Apache Samza, Apache Spark, and Apache Storm. Given the pivotal role that state management plays, particularly, for iterative batch and stream processing, in this survey, we present examples of state as an enabler, discuss the alternative approaches used to handle and implement state, capture the many facets of state management, and highlight new research directions. Our aim is to provide insight into disparate state management techniques, motivate others to pursue research in this area, and draw attention to open problems.

For several decades, optical networks, due to their high capacity and long-distance transmission range, have been used as the major communication technology to serve network traffic, especially in the core and metro segments of communication networks. Unfortunately, our society has often experienced how the correct functioning of these critical infrastructures can be substantially hindered by massive failures triggered by natural disasters, weather-related disruptions and malicious human activities. In this position paper, we discuss the impact on optical networks of all major classes of disaster events mentioned above, and we overview recent relevant techniques that have been proposed to increase the disaster resilience of optical networks against the various classes of disaster events. We start by presenting some proactive methods to be applied before the occurrence of a disaster. Then we move our focus also on other preparedness methods that can be executed in the (typically short) time frame between the occurrence of an early alert of an incoming disaster and the time a disaster actually hits the network. Finally, we discuss reactive procedures that allow performing post-disaster recovery operations effectively. The analysis of disaster resilience mechanisms provided in this paper covers both wired and optical wireless communication infrastructures and also contains explicit remarks covering the role of emerging technologies (e.g., fixed-mobile convergence in the 5G era and beyond) in disaster resilience.

Establishing multicast communications in MPLS-capable networks is an essential requirement for a wide-scale deployment of MPLS in the Internet. This paper outlines a framework for the setup of a MultiPoint-to-MultiPoint (MP2MP) Label Switched Path (LSP) for establishing uni-directional multicast shared trees. The presented framework is intended for multicast applications within a single autonomous domain and can be extended to cover inter-domain multicast sessions. We propose the use of one (or more) control points in the network called Rendez-vous Points (RP) in a manner similar to PIM-SM shared trees. Senders of the multicast session have to register with the RP and establish unicast LSPs with the RP. Receivers who join the session have to send their join requests to the RP which acts as a root (and the sender) of a one-to-many tree by establishing a Point-to-MultiPoint (P2MP) LSP between the RP and the receiver. This architecture utilizes more than one RP to implement RP failure recovery, to provide load balancing within the domain, and to enable the extension of this framework to multiple domains by establishing LSPs between RPs in different domains. This architecture also has the advantage of using existing MPLS techniques and existing routing protocols and requires only the addition of more management capabilities at the RPs. The paper explains the framework in details and provides an example on how to set the LSP on a given topology. We also refer to some preliminary simulation results testing the scalability of the architecture in comparison with traditional multicast routing.

This paper presents a study of our proposed architecture for the setup of a MultiPoint-to-MultiPoint (MP2MP) Label Switched Path (LSP). This form of LSP is needed for establishing uni-directional multicast shared trees. Such trees are required for information distribution in applications such as video conferencing. The presented architecture is intended for multicast applications within a single autonomous domain and can be extended to cover inter-domain multicast sessions. We propose the use of one (or more) control points in the network called Rendez-vous Points (RP) in a simple extention of the PIM-SM protocol to implement multicast in MPLS networks. This architecture has the advantage of using existing MPLS techniques and existing routing protocols and requires only the addition of more management capabilities at the RPs. The experiments we carried out show that while retaining the advantages of using MPLS over traditional multicast routing, the performance of the new architecture is comparable to that of IP multicast in terms of the volume of control messages and label and memory consumption. Also the architecture scales well with the increase of the number of senders within a multicast group and with the increase of the number of multicast groups.

In this paper, we investigate distributed mutual exclusion algorithms and delineate the features of a new distributed mutual exclusion algorithm. The basis of the algorithm is the logical ring structure employed in token-based mutual exclusion algorithms. Specifically, there exists dynamic properties of the logical ring that, given certain restrictions regarding message traffic flow, passively give useful information about the location

Wireless sensor networks (WSN) have been investigated as a powerful distributed sensing application to enhance the efficiency of embedded systems and wireless networking capabilities. Although WSN has offered unique opportunities to set the foundation for using ubiquitous and pervasive computing, it suffered from several issues and challenges such as frequently changing network topology and congestion issue which affect not only network bandwidth usage but also performance. The main objective of this study is to introduce a congestion-aware clustering and routing (CCR) protocol to alleviate the congestion issue over the network. The CCR protocol is proposed to decrease end-to-end delay time and prolong the network lifetime through choosing the suitable primary cluster head (PCH) and the secondary cluster head (SCH). The experimental results demonstrate that the effectiveness of the CCR protocol to satisfy the quality of service (QoS) requirements in increasing the network lifetime and raising the number of packets sent alike. Moreover, the CCR outperforms other state-of-the-art techniques in decreasing the overflow of data, and thus the network bandwidth usage is reduced. INDEX TERMS Congestion control, clustering protocols, pervasive computing, quality of service (QoS), routing protocols, ubiquitous computing, wireless sensor network (WSN).

We have built a software layer on top of Mach 2.5 that recovers multitask Mach applications from fail-stop failures. The layer implements Optimistic Recovery (OR), a mechanism for transparent recovery from failing tasks and processors, based on asynchronous checkpointing and logging of inter{task messages. OR recovers from failure by restoring a checkpoint and replaying the logged messages. The current prototype supports message communication via sends and receives, simple port operations, and task interactions through the environment manager. This paper discusses the issues Mach raised for this implementation, the structure of the OR layer, the design of future enhancements, and comparisons with other recovery techniques.

The aim of this paper is to convey our experience using the ESA's 3DROV planetary rover simulator as a visualization and validation tool through a dynamic analysis on the performance of an advanced autonomous control architecture: a power-aware, model-based control system with applications in rover-based mission operations which integrates advanced constraint-based reasoning within a flexible control execution management process. The analysis focuses on the validation of the main capabilities of the control system through three representative simulation examples executed upon an integrated testbed platform with 3DROV. More concretely, the target of the simulation tests is twofold: (i) to demonstrate the main capabilities of the controller; and (ii) to evaluate its performance on overcoming specific anomalous situations which might threaten the whole mission execution success.

This paper aims at describing an integrated power-aware, model-based autonomous control architecture for planetary rover-based mission operations synthesized in the context of a Ph.D. program on the topic "Autonomy for Interplanetary missions" funded and supported by ESA. The proposed controller implements a single Sense-Act-Plan (SPA) closed-execution loop to safely command the robot activities considered in the context of a specific key mission scenario. Both highly decisionmaking capabilities and a flexible execution process are the two key features on which the control system is grounded. Furthermore, target execution capabilities, specially those that allow to flexibly keeping pace with temporal and power-related contingencies that might threaten the whole schedule execution attainment, are demonstrated through the integration with the ESA's 3DROV planetary rover system simulator.

Improving the computation efficiency is the key issue in image processing, especially in edge detection, because edge detection is very computationally intensive. With the development of real-time image processing application, fast processing response is becoming the major requirement in this area. In this paper, a parallel and distributed algorithm on Spiral Architecture for edge detection using a uni-directional MultiRing is proposed. The proposed algorithm is based on Master-Slave model. It guarantees a better load balancing among the processors (or nodes) and greatly reduces the traffic from and to the master node. It uses each MultiRing configuration more efficiently. It also improves the performance for message passing among the modes on the MultiRing.

WDM optical networks are high speed networks and provide enormous capacity. Survivability is very important issue in these networks. Survivability requires resources for handling the failures. So, efficient resource allocation strategy is required for survivability. In this paper, we have presented two resource allocation strategies for survivability. These strategies reserve the resources for the primary lightpaths and backup lightpaths. Then extensive simulations are done on different networks to evaluate the performance in terms of blocking probability. The results show that the second strategy performs better than first strategy.

In this paper, we have addressed the complex problem of determining a recovery line for cluster federation and proposed an efficient checkpointing / recovery mechanism for it. The main objective of the proposed approach is to advance the recovery line in a cluster federation such that we can put a limit on the amount of rollback by the processes in all the clusters in case of failure(s) in the cluster federation; thereby in the worst case only limited domino effect is allowed in our work. In this approach, processes in different clusters are able to perform their responsibility independently and simultaneously. This inherent parallelism of the algorithm contributes to its speed of execution. We have shown that the proposed approach is superior to the existing works, because neither it suffers from any message storm, nor it takes any unnecessary checkpoints.

We describe a new scalable application-layer multicast protocol, specifically designed for low-bandwidth, data streaming applications with large receiver sets. Our scheme is based upon a hierarchical clustering of the application-layer multicast peers and can support a number of different data delivery trees with desirable properties.We present extensive simulations of both our protocol and the Narada application-layer multicast protocol over Internet-like topologies. Our results show that for groups of size 32 or more, our protocol has lower link stress (by about 25%), improved or similar end-to-end latencies and similar failure recovery properties. More importantly, it is able to achieve these results by using orders of magnitude lower control traffic.Finally, we present results from our wide-area testbed in which we experimented with 32-100 member groups distributed over 8 different sites. In our experiments, average group members established and maintained low-latency paths and ...

A composite web service is essentially a combination of smaller services to provide extended functionalities. However, such services are more susceptible to failures than atomic services. This is due to its dependency on other services which are external modules to the composite service. In this paper, we introduce a heuristic distance measure which significantly reduces search space of hybrid (i.e. forward-backward) search algorithm and results in near-optimal solutions.

In the Microbial typing field, the need to have a common understanding of the concepts described and the ability to share results within the community is an increasingly important requisite for the continued development of portable and accurate sequence-based typing methods. These methods are used for bacterial strain identification and are fundamental tools in Clinical Microbiology and Bacterial Population Genetics studies. In this article we propose an ontology designed for the microbial typing field, focusing on the widely used Multi Locus Sequence Typing methodology, and a RESTful API for accessing information systems based on the proposed ontology. This constitutes an important first step to accurately describe, analyze, curate, and manage information for microbial typing methodologies based on sequence based typing methodologies, and allows for the future integration with data analysis Web services.

In this paper we propose a quasi-synchronous checkpointing algorithm and a low-overhead recovery algorithm based on it. The checkpointing algorithm preserves process autonomy by allowing them to take checkpoints asynchronously and uses communication-induced checkpoint coordination for the progression of the recovery line which helps bound rollback propagation during a recovery. Thus, it has the easertess and low overhead of asynchronous checkpointing and the recovery time advantages of synchronous checkpointing. There is no extra message overhead involved during checkpointing and the additional checkpointing overhead is nominal. The algorithm ensures the existence of a recovery line consistent with the latest checkpoint of any process all the time. The recovery algorithm exploits this feature to restore the system to a state consistent with the latest checkpoint of afailedprocess. The recovery algorithm has no domino effect and a failed process needs only to rollback to its latest checkpoint and request the other processes to roll back to a consistent checkpoint. To avoid domino effect, it uses selective pessimistic message logging at the receiver end. The recovery is asynchronousfor single process failure. Neither the recovery algorithm nor the checkpointing algorithm requires the channels to be FIFO. We do not use vector timestamps for determining dependency between checkpoints since vector timestamps generally result in high message overhead during failure-free operation. uses the checkpoints and message logs to restore the system to a consistent global state [12]. In the literature, several checkpointing schemes have been proposed for distributed systems. They can be broadly classified into two categories asynchronous and synchronous. In asynchronous checkpointing [3], processes take checkpoints periodically without any coordination with others. To recover from a failure, a process communicates with other processes to determine if their local states are causally related. If they are. processes that received messages which are responsible for causal dependencies, roll back to eliminate these causal dependencies. This process is repeated until the local states of all the processes are free from causal dependencies. This approach allows maximum process autonomy and has low checkpointing overhead. However, this approach may suffer from the domino effect, in which the processes roll back recursively while determining a consistent set of checkpoints. To reduce domino effect, Kim et al. [9] and Venkatesh et al. [17] use the dependency tracking and insert checkpoints before processing a new message that introduces dependency. Message logging [6, 7, 14, 161 and message reordering [ 191 have been suggested in the literature to cope with the domino effect.

Finding consistent global checkpoints of a distributed computation is important for analyzing, testing, or verifying properties of these computations. In this paper we present a theoretical foundation for nding consistent global checkpoints. Given an arbitrary set S of local checkpoints, we prove exactly which sets of other local checkpoints can be combined with S to build consistent global checkpoints, and we present an algorithm for nding all such global checkpoints. The minimal and maximal consistent global checkpoints are presented as special cases. The results are based on the notion of zigzag paths introduced by Netzer and Xu 14]. We also present a method for nding zigzag paths using the rollback-dependency graph introduced by Wang 17, 16].

Checkpointing algorithms are classi ed as synchronous and asynchronous in the literature. In synchronous checkpointing, processes synchronize their checkpointing activities so that a globally consistent set of checkpoints is always maintained in the system. Synchronizing checkpointing activity involves message overhead and process execution may have to be suspended during the checkpointing coordination, resulting in performance degradation. In asynchronous checkpointing, processes take checkpoints without any coordination with others. Asynchronous checkpointing provides maximum autonomy for processes to take checkpoints; however, some of the checkpoints taken may not lie on any consistent global checkpoint, thus making the checkpointing efforts useless. Asynchronous checkpointing algorithms in the literature can reduce the number of useless checkpoints by making processes take communication induced checkpoints, besides asynchronous checkpoints. We call such algorithms, quasi-synchronous. Quasi-synchronous checkpointing algorithms are attractive because they improve the performance without introducing undesirable e ects. In this paper, we present a theoretical framework for characterizing and classifying such algorithms. The theory not only helps to classify and characterize the quasi-synchronous checkpointing algorithms, but also helps analyzing the properties and limitations of the algorithms belonging to each class; it also provides guidelines for designing and evaluating such algorithms. This classi cation also sheds light on some open problems that remain to be solved.

Advance reservation of lightpaths in grid environments is necessary to guarantee QoS and reliability. In this paper, we have evaluated and compared several algorithms for dynamic scheduling of lightpaths using a flexible advance reservation model. The main aim is to find the best scheduling policy for a grid network resource manager that improves network utilization and minimizes blocking. The scheduling of lightpaths involves both routing and wavelength assignment. Our simulation results show that minimum‐cost adaptive routing where link costs are determined by the current and future usage of the link provides the minimum blocking. For wavelength assignment, we have used a scheme that reduces fragmentation by minimizing unused gaps. We have also analyzed approaches for failure recovery and resource optimization. Copyright © 2008 John Wiley & Sons, Ltd.

Handling faults is a growing concern in HPC. In future exascale systems, it is projected that silent undetected errors will occur several times a day, increasing the occurrence of corrupted results. In this article, we propose SEDAR, which is a methodology that improves system reliability against transient faults when running parallel message-passing applications. Our approach, based on process replication for detection, combined with different levels of checkpointing for automatic recovery, has the goal of helping users of scientific applications to obtain executions with correct results. SEDAR is structured in three levels: (1) only detection and safestop with notification; (2) recovery based on multiple system-level checkpoints; and (3) recovery based on a single valid user-level checkpoint. As each of these variants supplies a particular coverage but involves limitations and implementation costs, SEDAR can be adapted to the needs of the system. In this work, a description of the methodology is presented and the temporal behavior of employing each SEDAR strategy is mathematically described, both in the absence and presence of faults. A model that considers all the fault scenarios on a test application is introduced to show the validity of the detection and recovery mechanisms. An overhead evaluation of each variant is performed with applications involving different communication patterns; this is also used to extract guidelines about when it is beneficial to employ each SEDAR protection level. As a result, we show its efficacy and viability to tolerate transient faults in target HPC environments.

In this paper a distributed routing management solution is described that takes into consideration statistical Quality of Service (QoS) information about the state of network links. The goal is to offer dynamic metrics to the routing algorithm based on the current resource utilization, i.e. the routing metrics will depend on the traffic load and the delay measured on individual links in real-time. Identification of congested areas allows situation-aware path selection, enhancing the global capacity of the network by determining optimal routes. Streszczenie. W artykule przedstawiono sposób zarz dzania routowaniem, w którym wzi to pod uwag parameter QoS na temat stanu linków w sieci. G ównym celem by o zastosowanie dynamicznej metryki do algorytmu routowania, opartej na informacji o bie cym wykorzystaniu zasobów. Identyfikacja rejonów przeci enia pozwala na polepszenie dzia ania i pojemno ci sieci poprzez optymalizacj cie ki routowania. (Kontrola przeci enia w routowaniu QoS).

This document defines the architecture for IP and LDP Fast Reroute using Maximally Redundant Trees (MRT-FRR). MRT-FRR is a technology that gives link-protection and node-protection with 100% coverage in any network topology that is still connected after the failure. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7812.

Istituto di Linguistica Computazionale – CNR1 Area della Ricerca, via G. Moruzzi 1, 56100 Pisa, Italy {roberto.bartolini, simonetta.montemagni, vito.pirrelli}@ilc.cnr.it ... Università di Pisa, Dipartimento di Linguistica2 via Santa Maria, 36, 56100 Pisa, Italy ...

In a single link network architecture if a link fails, system hunts for the substitute link and transmits the data through that link. It is always necessary for system to search the reason for path break then configure the system again to transmit the data through other path/node. But during the transmission there are more chances of packet loss or delay. In this paper we propose a mechanism to overcome from the packet loss or delay problem such that if any node or path breakdowns, it will assist in transmission of data without any packet loss or delay.

Fault-tolerance is an essential aspect of network resilience. Fault-tolerance mechanisms are required to ensure high availability and high reliability in systems. The advent of software-defined networking (SDN) has both presented new challenges and opened new paths to develop novel strategies, architectures, and standards to support fault-tolerance. In this survey, we address SDN fault-tolerance and discuss the OpenFlow fault-tolerance support for failure recovery. We highlight the mechanism used for failure recovery in Carrier-grade networks that includes detection and recovery phases. Furthermore, we highlight SDN-specific fault-tolerance issues and provide a comprehensive overview of the state-ofthe-art SDN fault-tolerance research efforts. We then discuss and structure SDN fault-tolerance research according to three distinct SDN planes (i.e., data, control, and application). Finally, we conclude enumerating future research directions for SDN fault-tolerance development.

Multicasting is a fundamental networking primitive utilized by numerous applications. This also holds true for cognitive radio networks (CRNs) which have been proposed as a solution to the problems that emanate from the static non-adaptive features of classical wireless networks. A prime application of CRNs is dynamic spectrum access (DSA), which improves the efficiency of spectrum allocation by allowing a secondary network, comprising of secondary users (SUs), to share spectrum licensed to a primary licensed networks comprising of primary users (PUs). Multicasting in CRNs is a challenging problem due to the dynamic nature of spectrum opportunities available to the SUs. Various approaches, including those based in optimization theory, network coding, algorithms, have been proposed for performing efficient multicast in CRNs. In this paper, we provide a self-contained tutorial on algorithms and techniques useful for solving the multicast problem, and then provide a comprehensive survey of protocols that have been proposed for multicasting in CRNs. We conclude this paper by identifying open research questions and future research directions.

Availability in software refers to the system's ability to be operational and ready to perform its tasks when required. This concept is broader than reliability, as it includes not only consistent performance but also the system's capacity for recovery. When a system encounters a failure, availability ensures that it can repair itself, using various techniques to either mask or fix faults before they escalate into failures. This ensures that the overall downtime remains within acceptable limits over a specified time period. Availability, therefore, subsumes reliability, robustness, and other related quality attributes focused on avoiding unacceptable failures.

Tha Ncvr Millennium Remote Agent (NMRA) will be the first AI system to control an actual spacecraft. The spacecraft domain places a strong premium on autonomy and requires dynamic recoveries and robust concurrent execution, all in the presence of tight real-time deadlines, changing goals, scarce resource constraints, and a wide variety of possiblo failures. To achieve this level of execution robustness, wo 11ixw integrated a procedural executive based on generic proccdurca with a deductive model-based executive. A procedural executive provides sophisticated control constructs such as loops, parallel ectivity, locks, and synchronization which arc used for robust schedule execution, hierarchical task decomposition, and routine configuration management. A dcductivc cxccutive provides algorithms for sophisticated state infcrencc and optimal failure recovery planning. The intograted executive enables designers to code knowledge via a combination of procedures and declarative models, yielding a rich modeling capability suitable to the challenges of ranl spacecraft control, The interface between the two exccutivcs ensures both that recovery sequences are smoothly merged into high-level schedule execution and that a high dcgrcc of reactivity is retained to effectively handle sdditional failures during recovery. 'Thla papor describes work partiolly performed at the Jet Propuldon Loborntory,

Resource allocation is most needed in the next generation of Cognitive radio networks these techniques are used to increase the Cognitive radio network's performance. But, it is difficult to accomplish these techniques in real-time performance wireless. In this paper, a resource allocation technique based on artificial neural networks (ANN) is proposed which helps to reduce the power consumption in the network. The goal of the proposed scheme is to secure data transmission and to increase the uplink and downlink speed with less bit error rate. From the Simulation results, it can be observed that the proposed technique based on ANN is efficient in terms of the computation time related to the other resource allocation techniques. To increase the security of the data transmission in networks Location-based key management system is used. This paper is implemented by NS2.

R esearch in consumer psychology shows that customers seek reasons for service failures and that attributions of blame moderate the effects of failure on the level of customer satisfaction. This paper extends research on service operations failures by hypothesizing that attributions of blame also affect what matters to the customer during service failures. Specifically, we hypothesize that the relative weights that customers assign to key service elements in reaching an overall assessment of customer satisfaction are affected by customer attributions of blame for service failures. We use the U.S. airline industry as a quasi-experimental research setting to investigate the components of customer satisfaction for three samples of customers who experience (1) routine service, (2) flight delays of external (i.e., weather) origin, and (3) flight delays of internal origin. Although the level of customer satisfaction is lower for all service failures, we find that the key components of satisfaction differ between delayed and routine flights only when customers blame the service provider for the failure. Specifically, when delays are of external origin satisfaction is lower than for routine flights, but there is virtually no difference in the weight that customers assign to the components of customer satisfaction (including employee interactions). In contrast, when delays are of internal origin, satisfaction is lower than for either routine flights or flights delayed by external factors, and employee interactions have a significantly diminished role in customer satisfaction evaluations. Contrary to the popular view that employee interactions take on a greater role in determining customer satisfaction during service failures, we find that the opposite is true if the customer attributes blame to the service provider. Our findings highlight the important role of customer attributions during service failures and present more nuanced evidence on the role of employee-customer interactions in mitigating the effects of service failures on customer satisfaction.

Service composition provides a flexible way to quickly enable new application functionalities in next generation networks. We focus on the scenario where next generation portal providers 'compose' the component services of other providers. We have developed an architecture based on an overlay network of service clusters to provide failure-resilient composition of services across the wide-area Internet: our algorithms detect and recover quickly from failures in composed client sessions. In this paper, we present an evaluation of our architecture whose overarching goal is quick recovery of client sessions. The evaluation of an Internet-scale system like ours is challenging. Simulations do not capture true workload conditions and Internet-wide deployments are often infeasible. We have developed an emulation platform for our evaluation-one that allows a realistic and controlled design study. Our experiments show that the control overhead involved in implementing our recovery mechanism is minimal in terms of network as well as processor resources; minimal additional provisioning is required for this. Failure recovery can be effected using alternate service replicas within about 1 s after failure detection on Internet paths. We collect trace data to show that failure detection itself can be tight on wide-area Internet paths-within about 1.8 s. Failure detection and recovery within these time bounds represents a significant improvement over existing Internet path recovery mechanisms that take several tens of seconds to a few minutes.

In KU-FEL (Kyoto University FEL) 12-14 m FEL has been available by using a 40 MeV S-band linac and 1.6 m undulator. We are going to install 1.8 m undulator which was used in JAEA to extend the lasing range of KU-FEL. We measured the undulator field and evaluated the FEL gain to confirm the possible lasing range. The measured magnetic field showed large de-magnetization in several %. Numerical evaluation of the lasing range has been carried out by using GENESIS1.3 and the result showed the expected FEL gain with the 1.8-m undulator (10%) which was smaller than that with 1.6-m undulator (20%). We simulated a magnetic sorting for 1.8-m undulator and FEL gain was recovered to be (30%).

This paper proposes an approach to examining how testing affects the operational behavior of aging software systems. Such an approach requires models for the testing phase and the operational phase that explicitly account for crash failures due to both aging-related and non-aging-related bugs. We develop appropriate semi-Markov models and derive expressions for computing the respective transient and steady-state probabilities needed. Our numerical examples suggest that disregarding the effects of non-aging-related bugs can result in wrong conclusions about the testing phase and the operational phase. Moreover, we show how to combine the two models for a joint analysis in which metrics of interest concerning the operational phase, like the optimal rejuvenation rate, are random variables whose distributions are influenced by the potential outcomes of testing.

Under link-state routing protocols such as OSPF and IS-IS, when there is a change in the topology, propagation of link-state announcements, path recomputation, and updating of forwarding tables (FIBs) will all incur some delay before traffic forwarding can resume on alternate paths. During this convergence period, routers may have inconsistent views of the network, resulting in transient forwarding loops. Previous remedies proposed to address this issue enforce a certain order among the nodes in which they update their FIBs. While such approaches succeed in avoiding transient loops, they incur additional message overhead and increased convergence delay. We propose an alternate approach, loopless interface-specific forwarding (LISF), that averts transient loops by forwarding a packet based on both its incoming interface and destination. LISF requires no modifications to the existing link-state routing mechanisms. It is easily deployable with current routers since they already maintain a FIB at each interface for lookup efficiency. This paper presents the LISF approach, proves its correctness, discusses three alternative implementations of it and evaluates their performance.

Under link-state routing protocols such as OSPF and IS-IS, when there is a change in the topology, propagation of link-state advertisements, path recomputation, and updating of forwarding tables (FIBs) will all incur some delay before traffic forwarding can resume on alternate paths. During this convergence period, routers may have inconsistent views of the network, resulting in transient forwarding loops. Previous remedies proposed to address this issue enforce a certain order among the nodes in which they update their FIBs. While such approaches succeed in avoiding transient loops, they incur additional message overhead and/or increased convergence delay. We explore an alternative approach, loopless interface-specific forwarding (LISF), that mitigates transient loops by forwarding a packet based on both its incoming interface and destination address. LISF needs to compute and update interface-specific instead of interface-independent forwarding tables. But it requires neither the synchronization of FIB updates at different nodes nor the modification of the existing link-state routing mechanisms. LISF is easily deployable with current routers if they already maintain a FIB at each interface for lookup efficiency. This paper presents the LISF approach, illustrates its strengths and limitations, discusses four alternative implementations of it and evaluates their performance.

Overlay multicast scheme has been regarded as an alternative to conventional IP multicast since it can support multicast functions without infrastructural level changes. However, multicast tree reconstruction procedure is required when a non-leaf node fails or leaves. In this paper, we propose a proactive approach to solve the aforementioned defect of overlay multicast scheme by using a resource reservation of some nodes' out-degrees in the tree construction procedure. In our proposal, a proactive route maintenance approach makes it possible to shorten recovery time from parent node's abrupt failure. The simulation results show that proposed approach takes less time than the existing works to reconstruct a similar tree and that it is a more effective way to deal with more nodes that have lost their parent nodes due to failure.

The aim of this paper is to move away from today's multi-tier, manually operated, and performance limited Data Centre Network (DCN) towards more scalable, flexible, and optimized architecture of tomorrow. We propose a new hybrid optical DCN architecture capable of providing a fully optical interconnection path from server to server within racks and between racks utilizing fast packet switching at the aggregation layer, and high-capacity and low latency circuit switching at the core layer. We have built the DCN control plane upon the Software Defined Networks (SDN) paradigm to leverage the added value of emerging optical technologies for providing flexible and programmable heterogeneous IT and network service. Dynamicity, flexibility, and resiliency are combined in the propose infrastructure to offer advanced services to the data centre providers in order to fulfil the requirements of upcoming applications.

Wireless communications have seen remarkable progress over the past two decades and perceived tremendous success due to their agile nature and capability to provide fast and ubiquitous internet access. Maturation of 3G wireless network services, de-I would like to express my sincere gratitude to all people who supported me throughout the years of my PhD studies and beyond. First and foremost, I am truly indebted to my thesis supervisor, Dr. Chadi Assi, who is not only the most hard working person I have ever come across but also a dedicated and extremely helpful professor. It would have been impossible for me to accomplish this endeavor without his constant support, guidance and motivations. I'd also like to express my appreciation to all the faculty and people at Concordia University who contributed to my success one way or the other.