Group Of Servers Research Articles

A Note on a Multi-server Queue with Vacations of Multiple Groups of Servers

We study a Markovian queueing system with unreliable servers and two possible groups of servers taking two different types of vacations. Once the number of idle of servers reaches one of the two critical numbers in the system, a group of servers will take a single synchronous vacation (or leave for doing a secondary job). After taking the vacation, the servers return to attend the queue (or stay idle for the next arriving customer). Therefore, there can be a maximum of two groups of servers taking two different types of vacations at a time (doing some secondary jobs). The servers are subject to failure when attending the queue. The stability condition for the system and the stationary performance measures are developed by using the matrix-analytical method. A cost model is constructed to determine the optimal vacation policy and the optimal service rate of each server. Some numerical results are presented to illustrate the optimization procedures.

Factors involved in dentistry absenteeism since the foundation of the Labor Court from 1986 to 2008

Aim: To identify the most important factors involved in dentistry absenteeism since the foundation of the Labor Court in Campinas, SP, Brazil, until December 2008; to verify if there was a decrease in dentistry absenteeism after the introduction of the dental service in the headquarters of the Court; to verify if dentistry absenteeism is greater in the others cities of the region compared with the city of Campinas. Methods: The information was collected from the dental statements of the archives of the Health Department of the Labor Court. Collected information included: International Classification of Diseases (ICD-10), gender, age, function, origin of the statements, period of the absenteeism and year when the absence occurred. Results: 3,084 health files from server group (2,741) and judges (343) were reviewed. The results indicated: higher prevalence of female gender, higher frequency in the age group from 30 to 40 years old and the smallest frequency in the age group upper from 60 years old. It was found an average sick-leave period of 1.93 days. According to the International Classification of Diseases (ICD)-10, the most prevalent dental problems found in this study were: K01 (25.78%), K04 (10.57%) and K05 (6.37%). Conclusions: The results of this study pointed to lower rates of absenteeism than the results found in the literature. The introduction of the dental service did not have influence on the rates of absenteeism of the area; however it influenced the absenteeism rates in the city of Campinas (headquarters of the Court).

Optimal Load Distribution for Multiple Heterogeneous Blade Servers in a Cloud Computing Environment

Given a group of heterogeneous blade servers in a cloud computing environment or a data center of a cloud computing provider, each having its own size and speed and its own amount of preloaded special tasks, we are facing the problem of optimal distribution of generic tasks over these blade servers, such that the average response time of generic tasks is minimized. Such performance optimization is important for a cloud computing provider to efficiently utilize all the available resources and to deliver the highest quality of service. We develop a queueing model for a group of heterogeneous blade servers, and formulate and solve the optimal load distribution problem of generic tasks for multiple heterogeneous blade servers in a cloud computing environment in two different situations, namely, special tasks with and without higher priority. Extensive numerical examples and data are demonstrated and some important observations are made. It is found that server sizes, server speeds, task execution requirement, and the arrival rates of special tasks all have significant impact on the average response time of generic tasks, especially when the total arrival rate of generic tasks is large. It is also found that the server size heterogeneity and the server speed heterogeneity do not have much impact on the average response time of generic tasks. Furthermore, larger (smaller, respectively) heterogeneity results in shorter (longer, respectively) average response time of generic tasks.

Cyclic stable matching for three-sided networking services

Three-sided relationship is very common in the social and economic area, e.g., the supplier–firm–buyer relationship, kidney exchange problem. The three-sided relationship can also be found in many scenarios of computer networking systems involving three types of agents, which we regard as three-sided networks. For example, in sensor networks, data are retrieved from data sources (sensors) and forwarded to users through a group of servers. In such three-sided networks, users always prefer to receive the best data services from data sources, data sources would choose servers that are more efficient to deliver their data, and servers try to satisfy more users. Such preferences form a specific cyclic relationship and how to optimally allocate network resources to satisfy preferences of all parties becomes a great challenge. In this paper, inspired by the three-sided stable matching, we model the Three-sided Matching with Size and Cyclic preference (TMSC) problem for data sources, servers and users, aiming to find a stable matching for them, where all their preferences are satisfied. TMSC is different from the traditional three-sided matching models, as each server may normally serve more than one users. We show that the problem of seeking an optimal stable matching with maximum cardinality is NP-hard and propose efficient algorithms for the restricted model of TMSC problem to find a stable matching. The effectiveness of the proposed algorithms is validated through extensive simulations.

CLIENT-PERCEIVED WEB PERFORMANCE KNOWLEDGE DISCOVERY THROUGH TURNING BANDS METHOD

Client-perceived web performance prediction is a challenging for the knowledge engineering community. This article presents the application of the turning bands (TB) method to discover knowledge about the client-perceived spatiotemporal web performance. The TB method is used to study spatial or spatiotemporal phenomena. We conducted an experimental study to apply this technique. The MWING system was used to collect performance measurement for four clients, each monitoring the same group of web servers during several weeks of observations. In this article we present TB-based web performance prediction for an agent localized in Wrocław, Poland, and monitoring European web servers. The results of the spatial prediction of the total download web page times within a forecast of a two-week period showed that the TB simulation is efficient.

Research on the Model of the Internet of Things Servers Group Automatic Expandability Management and Control

The internet of things automatic expandability management and control technology are a key technology,which include adjusting member server numbers immediately according to load of servers group,optimizing internet of things servers system performance,making the system response time become fast,and making servers system energy consumption decrease.With the integrated technology research of detecting servers load,expandability management and control,load balance and so on ,the problem ,which is the internet of things servers group numbers are increased or decreased automatically when the internet of things servers load is too heavy or too light,is solved, servers group intelligent expandability and servers group intelligent load balance are realized.With system test,servers system performances and response times are improved obviously.

An Overview of File Server Group in Distributed Systems

The file server is a key factor to accomplish the data sharing essential in distributed systems. The file server is perhaps the most heavily used resource of the distributed systems and as an outcome; its performance is vital and critical to the victory of the system. The explosive growth of the Web contents and Internet users has led to increasing concentration on two major challenges in these systems: scalability and high availability of network file system. A simple load-sharing mechanism for the NFS client to switch to a lightly-load server based on the number of NFS client's RPC requests for a period of time, making these systems more efficient and scalable. The replication techniques are used for improving the availability of Distributed systems in FSG. We also discussed distributed application in terms of java programming language. In this paper we have proposed a new architecture for Distributed Systems that provides better security. Our proposed solution is more secure & efficient in the sense that a client can not search the whole group for a specific file, because the group header maintains a huge database of all the group members along with their specific services they offers. Also load balancing mechanism is improved where the group header keeps a record of connected users to a specific server. Every group member is not required to advertise their state.

FunFOLD: an improved automated method for the prediction of ligand binding residues using 3D models of proteins

BackgroundThe accurate prediction of ligand binding residues from amino acid sequences is important for the automated functional annotation of novel proteins. In the previous two CASP experiments, the most successful methods in the function prediction category were those which used structural superpositions of 3D models and related templates with bound ligands in order to identify putative contacting residues. However, whilst most of this prediction process can be automated, visual inspection and manual adjustments of parameters, such as the distance thresholds used for each target, have often been required to prevent over prediction. Here we describe a novel method FunFOLD, which uses an automatic approach for cluster identification and residue selection. The software provided can easily be integrated into existing fold recognition servers, requiring only a 3D model and list of templates as inputs. A simple web interface is also provided allowing access to non-expert users. The method has been benchmarked against the top servers and manual prediction groups tested at both CASP8 and CASP9.ResultsThe FunFOLD method shows a significant improvement over the best available servers and is shown to be competitive with the top manual prediction groups that were tested at CASP8. The FunFOLD method is also competitive with both the top server and manual methods tested at CASP9. When tested using common subsets of targets, the predictions from FunFOLD are shown to achieve a significantly higher mean Matthews Correlation Coefficient (MCC) scores and Binding-site Distance Test (BDT) scores than all server methods that were tested at CASP8. Testing on the CASP9 set showed no statistically significant separation in performance between FunFOLD and the other top server groups tested.ConclusionsThe FunFOLD software is freely available as both a standalone package and a prediction server, providing competitive ligand binding site residue predictions for expert and non-expert users alike. The software provides a new fully automated approach for structure based function prediction using 3D models of proteins.

Architecture, Implementation, and Experiments of Programmable Network Using OpenFlow

We propose a flexible and scalable architecture for a network controller platform used for OpenFlow. The OpenFlow technology was proposed as a means for researchers, network service creators, and others to easily design, test, and virtually deploy their innovative ideas in a large network infrastructure, which will accelerate research activities on Future Internet architectures. The technology enables the independent evolution of the network control plane and the data plane. Rather than having programmability within each network node, the separated OpenFlow controller provides network control through pluggable software. Our proposed network controller architecture will enable researchers to use their own software to control their own virtual networks. Flexibility and scalability were achieved by designing the network controller as a modularized and distributed system on a cluster of servers. Testing showed that a group of servers can efficiently cooperate to serve as a scalable OpenFlow controller. Testing using the nationwide JGN2plus network demonstrated that high-definition video can be delivered through OpenFlow-based point-to-point and point-to-multipoint paths.

Dynamic Service Assignment based on Proportional Ordering for the Adaptive Resource Management of Cloud Systems

The key issue in providing fast and reliable access on cloud services is the effective management of resources in a cloud system. However, the high variation in cloud service access rates affects the system performance considerably when there are no default routines to handle this type of occurrence. Adaptive techniques are used in resource management to support robust systems and maintain well-balanced loads within the servers. This paper presents an adaptive resource management for cloud systems which supports the integration of intelligent methods to promote quality of service (QoS) in provisioning of cloud services. A technique of dynamically assigning cloud services to a group of cloud servers is proposed for the adaptive resource management. Initially, cloud services are collected based on the excess cloud services load and then these are deployed to the assigned cloud servers. The assignment function uses the proposed proportional ordering which efficiently assigns cloud services based on its resource consumption. The difference in resource consumption rate in all nodes is analyzed periodically which decides the execution of service assignment. Performance evaluation showed that the proposed dynamic service assignment (DSA) performed best in throughput performance compared to other resource allocation algorithms.

Zyzzyva

A longstanding vision in distributed systems is to build reliable systems from unreliable components. An enticing formulation of this vision is Byzantine Fault-Tolerant (BFT) state machine replication, in which a group of servers collectively act as a correct server even if some of the servers misbehave or malfunction in arbitrary (“Byzantine”) ways. Despite this promise, practitioners hesitate to deploy BFT systems, at least partly because of the perception that BFT must impose high overheads. In this article, we present Zyzzyva, a protocol that uses speculation to reduce the cost of BFT replication. In Zyzzyva, replicas reply to a client's request without first running an expensive three-phase commit protocol to agree on the order to process requests. Instead, they optimistically adopt the order proposed by a primary server, process the request, and reply immediately to the client. If the primary is faulty, replicas can become temporarily inconsistent with one another, but clients detect inconsistencies, help correct replicas converge on a single total ordering of requests, and only rely on responses that are consistent with this total order. This approach allows Zyzzyva to reduce replication overheads to near their theoretical minima and to achieve throughputs of tens of thousands of requests per second, making BFT replication practical for a broad range of demanding services.

Pooling is not the answer

Abstract This note studies practical and theoretical scenarios to improve a completely pooled or unpooled scenario for two server groups (e.g. call center groups) with short and long jobs (e.g. calls). First, simple overflow (reported earlier) scenarios and priority rules are compared. Next, threshold rules are investigated for further practical improvement. Finally, a threshold rule is sought for a strict improvement over pooling for both short and long jobs. The practical value is illustrated numerically and appears to be consistent also for larger server numbers. The results show: (i) An overall average improvement by prioritizing short jobs. (ii) A slight but strict improvement over pooling by prioritizing long jobs. The first result is of practical interest; the second one is more theoretical. A practical scheme is provided for an ordering of scenarios, up to realistically large numbers of servers as in call centers.

The European Union, the United States, and Microsoft: A Comparative Review of Antitrust Doctrine

When a seller bundles together two products that have previously been sold separately, the arrangement is sometimes referred to as a tie. If the two products are bound together physically, it is often referred to as a technological tie. In the 1970s, IBM physically integrated so-called peripheral products, such as disk drives and printers which previously had been sold separately, into its central processing units. This integration was then attacked (largely unsuccessfully) by independent manufacturers of peripheral equipment as unlawful tying and as monopolization through tying. More recently, Microsoft has incorporated products, such as browsers and media players, into its operating system, behavior that again amounts to technological tying. It has also improved its server software by heightening the degree to which servers employing that software can interact. By raising the level of interaction among servers equipped with its software, Microsoft has so integrated work group servers as to enable groups of small servers to approach the capacities of mainframe computers. The European competition-law authorities see both matters as problematic. The integration of the media player has been condemned as tying; and the heightened server interaction has been faulted for failing to provide the interoperability that rival server software requires in order to participate on an equal footing with Microsoft server software in Windows work groups. Microsoft’s integration (at least in the view of the European antitrust authorities) also raises issues of essential facilities, and of the role of antitrust in achieving interoperability. Integration of these sorts - e.g., the hardware integrations of IBM and the software integrations of Microsoft - raise antitrust issues, as the extensive litigation in the United States and Europe over Microsoft’s behavior has revealed. We have now reached a moment in time in which both the American and European laws are sufficiently developed to warrant reflection and comparison. That is the task approached in this article. Part I, below, examines the European approach, exemplified in the decisions of the European Commission and the Court of First Instance about the interoperability of Microsoft’s server software. That part also examines the integration of the Windows Media Player into the Windows operating system. Part II reviews the U.S. decisions dealing with Microsoft’s integration of its Internet Explorer browser into its operating system. Since most readers will be familiar with the U.S. litigation at least in its main routlines, that review can be brief. Part III contains an initial comparison of the U.S. and European approaches to product integration. The conclusion in Part IV identifies the major differences and the doctrinal bases on which they rest.

Partitioning of Servers in Queueing Systems During Rush Hour

This paper is motivated by two phenomena observed in many queueing systems in practice. The first is the partitioning of server capacity among different customers based on their service time requirements. The second is rush hour demand where a large number of customers arrive over a short period of time followed by few or no arrivals for an extended period thereafter. We study a system with multiple parallel servers and multiple customer classes. The servers can be partitioned into server groups, each dedicated to a single customer class. The system operates under a rush hour regime with a large number of customers arriving at the beginning of the rush hour period. We show that this allows us to reduce the problem to one that is deterministic and for which closed-form solutions can be obtained. We compare the performance of the system with and without server partitioning during rush hour and address three basic questions. (1) Is partitioning beneficial to the system? (2) Is it equally beneficial to all customer classes? (3) If it is implemented, what is an optimal partition? We evaluate the applicability of our results to systems where customers arrive over time using (1) deterministic fluid models and (2) simulation models for systems with stochastic interarrival times.

Restaurant servers, tipping, and resistance

PurposeThe purpose of this paper is to present a next step in Greta Foff Paules' groundbreaking analysis of control‐resistance in service work by exploring the work practices of restaurant servers in regard to ways they resist and reshape the tipping system that structures their work life. Specifically, the author explores how workers will attempt to manipulate the system to elicit higher tips from customers and when servers forgo an economic tip, so that they can exercise dignity and self‐respect. Central to this analysis is to highlight the space in between Paules' notions of “getting” and “making” a tip. In this space, servers can exercise resistance and still acknowledge the humanness of the customer.Design/methodology/approachThe research methodology is participant observation and interviews.FindingsRestaurant servers see their ability to manipulate the tipping system as routes to exercising agency and resistance in work interactions. Moreover, servers see their ability to earn tips (and even forgo tips) by both capitalizing on the organizational structures and capitalizing on the customers' human nature.Research limitations/implicationsThe research focuses on servers broadly, and not on distinctions within groups of servers (i.e. sex differences, age differences or restaurant types).Originality/valueThis paper furthers the understanding of the tipping practice, which is historically viewed in terms of status inequality and control. In contrast, the author highlight how workers in practice, are able to use the tipping system to resist customer and manager demands, assert their creativity, agency, and self‐dignity, and still treat the customer as a social being.

A Task-Based Load Distribution Scheme for Multi-Server-Based Distributed Virtual Environment Systems

Multi-server-based distributed virtual environment (MSDVE) systems have become prevalent, supporting a large number of internet users. In MSDVEs, the load balancing among servers is an important issue to achieve system scalability. However, existing approaches must pay high migration overhead for the state transition of users or regions, thus the excessive holding time during load distribution makes it difficult for the system to keep the interactive performance acceptable. This paper aims to provide an efficient load distribution mechanism in which a group of servers takes charge of regions and shares region information among servers. The proposed mechanism dynamically classifies task types based on features of requested messages, and distributes each task fairly to neighboring servers. We have implemented the proposed mechanism extending our network framework for DVE, ATLAS, and our experiments show that the task distribution reduces both communication and processing overhead during load distribution without significant classification overhead.

ANALYSIS OF A MULTI-SERVER QUEUE WITH MARKOVIAN ARRIVALS AND SYNCHRONOUS PHASE TYPE VACATIONS

We study a MAP/M/c queueing system in which a group of servers take a simultaneous phase type vacation. The queueing model is studied as a QBD process. The steady-state analysis of the model including the waiting time distribution is presented. Interesting numerical results are discussed.

PERFORMANCE ANALYSIS OF OPTICAL BURST SWITCHED NETWORKS WITH LIMITED-RANGE WAVELENGTH CONVERSION, RETRANSMISSION AND BURST SEGMENTATION

This paper considers the performance of optical burst switched networks with burst segmentation, wavelength conversion and upper-layer retransmission. When a burst arrives at an intermediate node and finds its allocated wavelength occupied, it attempts to find another idle wavelength among a limited number of wavelengths to which the allocated wavelength can be converted. If the incoming burst cannot find any idle wavelength in the range, the ongoing burst in the allocated wavelength is segmented and its tail part which overlaps with the incoming burst is dropped and retransmitted as a retransmitted burst in a later time by upper-layer retransmission mechanisms such as TCP. Focusing on an outgoing optical fiber shared under wavelength division multiplexing, we model it as a multi-server retrial queueing system without waiting room, in which an arriving customer chooses his server out of a group of servers with a state-dependent probability. We formulate a bivariate Markov chain to analyze the model and also perform simulation experiments to validate the analysis model. Numerical examples show that the wavelength conversion technique is effective to lessen the contention of bursts at low traffic intensity and that the degree of contention among bursts is almost insensitive to the retransmission rate. They further reveal that even a small range of wavelength conversion can significantly alleviate the contention among bursts.

A Trust Model for a Group of E-mail Servers

E-mail services are essential in the Internet. However, the current e-mail architecture presents problems that open it to several threats. Alternatives have been proposed to solve some prob- lems related to e-mail services, offering reliability and scalability to such systems. This work presents a distributed trust model, allowing to create dynamic and decentralized trusted server lists, through the exclusion of servers recognized as spreaders of malicious messages. The trust model uses a social network approach and defines strategies for trust information update, propagation, and storage. A prototype was built to evaluate the proposed model’s effectiveness.

Zyzzyva

A longstanding vision in distributed systems is to build reliable systems from unreliable components. An enticing formulation of this vision is Byzantine fault-tolerant (BFT) state machine replication, in which a group of servers collectively act as a correct server even if some of the servers misbehave or malfunction in arbitrary (Byzantine) ways. Despite this promise, practitioners hesitate to deploy BFT systems at least partly because of the perception that BFT must impose high overheads. In this article, we present Zyzzyva, a protocol that uses speculation to reduce the cost of BFT replication. In Zyzzyva, replicas reply to a client's request without first running an expensive three-phase commit protocol to agree on the order to process requests. Instead, they optimistically adopt the order proposed by a primary server, process the request, and reply immediately to the client. If the primary is faulty, replicas can become temporarily inconsistent with one another, but clients detect inconsistencies, help correct replicas converge on a single total ordering of requests, and only rely on responses that are consistent with this total order. This approach allows Zyzzyva to reduce replication overheads to near their theoretical minima and to achieve throughputs of tens of thousands of requests per second, making BFT replication practical for a broad range of demanding services.