Wide-area Communication Research Articles

An agent-based approach for dynamic adjustment of scheduled jobs in computational grids

Grid computing is a newly developed technology for complex systems with large-scale resource sharing, wide-area communication, and multi-institutional collaboration. Grid scheduling is an important infrastructure in the grid computing environment. Most of the existing grids scheduling methods focus on maximizing processor utilization without taking grid load into consideration. This may lead to significant inefficiencies in performance such as large job queues and processing delays. In this paper, we propose a multiagent-based scheduling system for computational grids with a new approach. Agent technology is suitable for a computational grid because of the dynamic, heterogeneous, and autonomous nature of the grid. The main idea of the proposed system is a combination of a static scheduling using a fixed scheduling algorithm and a dynamic adjustment through the autonomous behavior of agents. The superiority of the proposed system, in reducing the load of the grid and minimizing the response time for executing user applications, is demonstrated by simulation experiments.

Distributed Load Balancing Model for Grid Computing

Most of the existing load balancing strategies were interested in distributed systems which were supposed to have homogeneous resources interconnected with homogeneous and fast networks. For Grid computing, these assumptions are not realistic because of heterogeneity, scalability and dynamicity characteristics. For these environments the load balancing problem is then a new challenge presently for which many research projects are under way. In this perspective, our contributions through this paper are two folds. First, we propose a distributed load balancing model which can represent any Grid topology into a forest structure. After that, we develop on this model, a load balancing strategy at two levels; its principal objectives : the reduction of average response time of tasks and their transferring cost. The proposed strategy is naturally distributed with a local decision, which allows the possibility of avoiding use of wide area communication network. La plupart des stratégies d’équilibrage de charge existantes se sont intéressées à des systèmes distribués supposés avoir des ressources homogènes interconnectées à l’aide de réseaux homogènes et à hauts débits. Pour les grilles de calcul, ces hypothèses ne sont pas réalistes à cause des caractéristiques d’hétérogénéité, de passage à l’échelle et de dynamicité. Pour ces environnements, le problème d’équilibrage de charge constitue donc, un nouveau défi pour lequel plusieurs recherches sont actuellement investies.Notre contribution dans cette perspective à travers ce papier est double: premièrement, nous proposons un modèle distribué d’équilibrage de charge, permettant de représenter n’importe quelle topologie de grille en une structure de forêt. Nous développons ensuite sur ce modèle, une stratégie d’équilibrage à deux niveaux ayant comme principaux objectifs la réduction du temps de réponse moyen et le coût de transfert de tâches. La stratégie proposée est de nature distribuée avec une prise de décision locale, ce qui permettra d’éviter le recours au réseau de communication à large échelle.

Cloudward bound

In this paper, we tackle challenges in migrating enterprise services into hybrid cloud-based deployments, where enterprise operations are partly hosted on-premise and partly in the cloud. Such hybrid architectures enable enterprises to benefit from cloud-based architectures, while honoring application performance requirements, and privacy restrictions on what services may be migrated to the cloud. We make several contributions. First, we highlight the complexity inherent in enterprise applications today in terms of their multi-tiered nature, large number of application components, and interdependencies. Second, we have developed a model to explore the benefits of a hybrid migration approach. Our model takes into account enterprise-specific constraints, cost savings, and increased transaction delays and wide-area communication costs that may result from the migration. Evaluations based on real enterprise applications and Azure-based cloud deployments show the benefits of a hybrid migration approach, and the importance of planning which components to migrate. Third, we shed insight on security policies associated with enterprise applications in data centers. We articulate the importance of ensuring assurable reconfiguration of security policies as enterprise applications are migrated to the cloud. We present algorithms to achieve this goal, and demonstrate their efficacy on realistic migration scenarios.

Security Technology for Smart Grid Networks

There is virtually universal agreement that it is necessary to upgrade the electric grid to increase overall system efficiency and reliability. Much of the technology currently in use by the grid is outdated and in many cases unreliable. There have been three major blackouts in the past ten years. The reliance on old technology leads to inefficient systems, costing unnecessary money to the utilities, consumers, and taxpayers. To upgrade the grid, and to operate an improved grid, will require significant dependence on distributed intelligence and broadband communication capabilities. The access and communications capabilities require the latest in proven security technology for extremely large, wide-area communications networks. This paper discusses key security technologies for a smart grid system, including public key infrastructures and trusted computing.

On the Benefit of Processor Coallocation in Multicluster Grid Systems

In multicluster grid systems, parallel applications may benefit from processor coallocation, that is, the simultaneous allocation of processors in multiple clusters. Although coallocation allows the allocation of more processors than available in a single cluster, it may severely increase the execution time of applications due to the relatively slow wide-area communication. The aim of this paper is to investigate the benefit of coallocation in multicluster grid systems, despite this drawback. To this end, we have conducted experiments in a real multicluster grid environment, as well as in a simulated environment, and we evaluate the performance of coallocation for various applications that range from computation-intensive to communication-intensive and for various system load settings. In addition, we compare the performance of scheduling policies that are specifically designed for coallocation. We demonstrate that considering latency in the resource selection phase improves the performance of coallocation, especially for communication-intensive parallel applications.

Satin

Computational grids have an enormous potential to provide compute power. However, this power remains largely unexploited today for most applications, except trivially parallel programs. Developing parallel grid applications simply is too difficult. Grids introduce several problems not encountered before, mainly due to the highly heterogeneous and dynamic computing and networking environment. Furthermore, failures occur frequently, and resources may be claimed by higher-priority jobs at any time. In this article, we solve these problems for an important class of applications: divide-and-conquer. We introduce a system called Satin that simplifies the development of parallel grid applications by providing a rich high-level programming model that completely hides communication. All grid issues are transparently handled in the runtime system, not by the programmer. Satin's programming model is based on Java, features spawn-sync primitives and shared objects, and uses asynchronous exceptions and an abort mechanism to support speculative parallelism. To allow an efficient implementation, Satin consistently exploits the idea that grids are hierarchically structured. Dynamic load-balancing is done with a novel cluster-aware scheduling algorithm that hides the long wide-area latencies by overlapping them with useful local work. Satin's shared object model lets the application define the consistency model it needs. If an application needs only loose consistency, it does not have to pay high performance penalties for wide-area communication and synchronization. We demonstrate how grid problems such as resource changes and failures can be handled transparently and efficiently. Finally, we show that adaptivity is important in grids. Satin can increase performance considerably by adding and removing compute resources automatically, based on the application's requirements and the utilization of the machines and networks in the grid. Using an extensive evaluation on real grids with up to 960 cores, we demonstrate that it is possible to provide a simple high-level programming model for divide-and-conquer applications, while achieving excellent performance on grids. At the same time, we show that the divide-and-conquer model scales better on large systems than the master-worker approach, since it has no single central bottleneck.

Steward: Scaling Byzantine Fault-Tolerant Replication to Wide Area Networks

This paper presents the first hierarchical byzantine fault-tolerant replication architecture suitable to systems that span multiple wide-area sites. The architecture confines the effects of any malicious replica to its local site, reduces message complexity of wide-area communication, and allows read-only queries to be performed locally within a site for the price of additional standard hardware. We present proofs that our algorithm provides safety and liveness properties. A prototype implementation is evaluated over several network topologies and is compared with a flat byzantine fault-tolerant approach. The experimental results show considerable improvement over flat byzantine replication algorithms, bringing the performance of byzantine replication closer to existing benign fault-tolerant replication techniques over wide area networks.

The Modeling and Verification of Peer-to-Peer Negotiating Multiagent Colored Petri Nets for Wide-Area Backup Protection

This paper focuses on the modeling and verification of a peer-to-peer wide-area backup protection (WABP) system. Agents located in a number of substation intelligent electronic devices (IEDs) negotiate on a peer, or equal, basis. The agent-based wide-area backup protection scheme is able to find power-line faults and protection misoperations. A wide-area communication network based on IP technology is used to transmit shared information among the agents. A novel agent-oriented peer-to-peer negotiating colored Petri net (AOPCPN) is proposed to implement the WABP system. The algorithms, design, and dynamic behavior of the WABP is evaluated in a simulated environment to demonstrate its benefits. The article begins by presenting the generic AOPCPN architecture and its formal definition. The AOPCPN model for the WABP multiagent system is evaluated according to one algorithm, which is detailed in this article. The WABP agent's autonomy, cooperation, parallel operation, and robustness are embodied in modules in order to ease the software engineering challenges in implementing and maintaining the agents. Three example scenarios illustrate the effectiveness of the Petri net model and its ability to dynamically respond to WABP misoperations and fault conditions.

Evolutionary construction of geographical networks with nearly optimal robustness and efficient routing properties

Robust and efficient design of networks on a realistic geographical space is one of the important issues for the realization of dependable communication systems. In this paper, based on a percolation theory and a geometric graph property, we investigate such a design from the following viewpoints: (1) network evolution according to a spatially heterogeneous population, (2) trimodal low degrees for the tolerant connectivity against both failures and attacks, and (3) decentralized routing within short paths. Furthermore, we point out the weakened tolerance by geographical constraints on local cycles, and propose a practical strategy by adding a small fraction of shortcut links between randomly chosen nodes in order to improve the robustness to a similar level to that of the optimal bimodal networks with a larger degree O ( N ) for the network size N . These properties will be useful for constructing future ad hoc networks in wide-area communications.

Provider link state bridging

Wide area communications technology has been challenged to virtualize large numbers of Ethernet LAN segments. This is a consequence of a mismatch between the broadcast nature of the LAN segment and the extremely constrained connectivity implied by the p2p connections or tunnels available in the WAN environment, which have been combined to create virtual LAN segments. PBB-TE has been a practical demonstration of how filtering applied to a broadcast media can result in a connection. This article introduces provider link state bridging (PLSB), which adds a control plane to the PBB data plane in order to extend the techniques for manipulation of Ethernet bridges for unicast paths pioneered by PBB-TE. PLSB solves the problem of largescale virtualization of LAN segments over an Ethernet infrastructure by applying advances in computation performance to the multicast capabilities inherent in the Ethernet data plane. The result is that the fundamental primitives of connectivity today, the broadcast LAN segment and the connection, can be virtualized in a scalable manner on a common (but substantially larger and better utilized) Ethernet-based infrastructure.

Availability Modeling and Cost Optimization for the Grid Resource Management System

Grid computing is a recently developed technique for complex systems with large-scale resource sharing, wide-area communication, and multi-institutional collaboration. Although the development tools and techniques for the grid have been extensively investigated, the availability of the grid resource management system (RMS) has not been comprehensively studied. In order to contribute to this lacking but important field, this paper first models the grid RMS availability by considering both the failures of resource management (RM) servers and the length limitation of request queues. A hierarchical Markov reward model is implemented to evaluate the grid RMS availability. Based on the availability model, an optimization problem for designing the grid RMS is studied in order to minimize the cost by determining the best number of RM servers. Then, the sensitivity analysis is conducted, and a dynamic switching scheduling method is further presented based on the sensitivity analysis.

A wireless wide area network picture archiving and communication system based on open source code and its clinical application

目的 建设一套价格低廉的基于Web的无线广域图像存储与传输系统(PACS).方法 对Internet上的开放源代码MyFreePACS进行改进.结果 建设了一套基于Web的无线广域PACS系统,利用IE浏览器调阅处理医学数字图像通讯接口(DICOM)图像,实现了图像的显示、存储等功能,并可在院内实现无线移动查房和通过Internet广域网进行远程影像会诊.结论 利用免费的开放源代码构建基于Web的经济型PACS在中小型医院切实可行,具有实用价值。

Scheduling Policies for Processor Coallocation in Multicluster Systems

Building multicluster systems out of multiple, geographically distributed clusters interconnected by high-speed wide-area networks can provide access to a larger computational power and to a wider range of resources. Jobs running on multiclusters and, more generally, in grids, may require (processor) coallocation, i.e., the simultaneous allocation of resources (processors) in different clusters or subsystems of a grid. In this paper, we propose four scheduling policies for processor coallocation in multiclusters, and we assess with simulations their performance under a wide variety of parameter settings. In particular, in our simulations we use synthetic workloads and workloads derived from the logs of actual systems and from runtime measurements. We conclude that although coallocation makes scheduling more difficult and the wide-area communication critically impacts the performance, there is a wide range of realistic applications that may benefit from coallocation. However, unrestricted coallocation is not recommended: Limiting the total job size or the number or the sizes of their components improves performance.

Aggregating Bandwidth for Multihomed Mobile Collaborative Communities

Multihomed, mobile wireless computing and communication devices can spontaneously form communities to logically combine and share the bandwidth of each other's wide-area communication links using inverse multiplexing. But, membership in such a community can be highly dynamic, as devices and their associated WWAN links randomly join and leave the community. We identify the issues and trade-offs faced in designing a decentralized inverse multiplexing system in this challenging setting and determine precisely how heterogeneous WWAN links should be characterized and when they should be added to, or deleted from, the shared pool. We then propose methods of choosing the appropriate channels on which to assign newly arriving application flows. Using video traffic as a motivating example, we demonstrate how significant performance gains can be realized by adapting allocation of the shared WWAN channels to specific application requirements. Our simulation and experimentation results show that collaborative bandwidth aggregation systems are, indeed, a practical and compelling means of achieving high-speed Internet access for groups of wireless computing devices beyond the reach of public or private access points

Carrier-Grade Ethernet Technologies for Next Generation Wide Area Ethernet

This paper describes an overview of overall carrier-grade Ethernet technologies for next generation wide area Ethernet. In recent years, from access network to metro and core network, we can find many areas where communication services are provided by Ethernet technologies. This comes from the fact that operational efficiency and economical efficiency of Ethernet are far better than that of conventional wide area communication technologies such as SONET and ATM. On the other hand, carrier-grade reliability, operations-administration-maintenance (OAM) and quality of service (QoS) are inferior to SONET and ATM. Various standard schemes in IEEE 802 and ITU-T and vendors' proprietary schemes can leave various approaches to solve these problems. In this paper, the author explains a basic architecture of wide area Ethernet service (Q-in-Q tagging for metro network and Mac-in-Mac encapsulation for core network) at first. Various switch control technologies are then discussed which are deployed or are under evaluation in order to improve (i) reliability (i.e., resiliency) to protect subscribers against network failures, (ii) OAM for providers to perform fault and performance management, and (iii) QoS to guarantee subscriber's service level agreement between a carrier and a subscriber. Finally, a new switching architecture, Global Open Ethernet (GOE), is also introduced as one of promising approaches to realize a next generation carrier-grade Ethernet.

New Static Var Compensator (SVC) based damping control using remote generator speed signal

Rapid advances in Wide-Area Measurement (WAM) and communication technologies have made the use of remote system data/signals for effective control and operation of power systems possible. This paper presents a new concept of damping control of Static Var Compensator (SVC) based on rotor speeds of remotely located generators. The concept is demonstrated in three study systems: a single machine infinite bus system, a two-area four-machine 11-bus system, and the Western System Coordinating Council (WSCC) three-machine nine-bus meshed system. The performance of the proposed remote generator speed signal is compared with the traditionally utilised local signals for SVC damping control through nonlinear time domain simulations. It is shown that the rotor speed of the remotely located generator that significantly participates in the lightly or negatively damped electromechanical mode of oscillation is the most effective SVC control signal in damping electromechanical oscillations in a power system.

Toward Grid-Aware Time Warp

The authors study the adaptation of an optimistic Time Warp kernel to cross-cluster computing on the Grid. Wide-area communication, the primary source of overhead, is offloaded onto dedicated routing processes. This allows the simulation processes to run at full speed and thus significantly decreases the performance gap caused by the wide-area distribution. Further improvements are obtained by employing message aggregation on the wide-area links and using a distributed global virtual time algorithm. The authors achieve many of their objectives for a cellular automaton simulation with lazy cancellation and moderate communication. High communication rates, especially with aggressive cancellation, present a challenge. This is confirmed by the experiments with synthetic loads. Even then, a satisfactory speedup can be achieved, provided that the computational grain of events is large enough.

Adaptive message scheduling for supporting causal ordering in wide-area group communications

Most of existing causal ordering protocols employ the passive message ordering (PMO) approach, which passively re-orders the disturbed messages at destinations. Since the PMO approach cannot prevent disturbance of message ordering, seriously disturbed messages can overrun the receiving buffer of these protocols and cause damaging message loss. This paper proposes the adaptive message scheduling (AMS) approach, which introduces scheduling latency for messages at sources to alleviate the disturbance of message ordering at destinations. We develop a theoretical base for calculating the value of scheduling latency. The scheduling latency can adapt to varying channel latency and is related to the message ordering relation and the message lifetime. We then describe a new protocol that employs the AMS approach. On basis of a proposed model for evaluating group communication protocols, we conduct experiments and simulations to validate the AMS approach. The simulation results show that the AMS approach can effectively improve the ordering latency and reduce the receiving buffer size. A small penalty of employing the AMS approach is a larger loss ratio if strict real-time delivery of messages is to be guaranteed.

A high‐throughput flow control scheme using a relay buffering function

AbstractAt present, window‐type flow control is mostly used in data communications in wide‐area networks. With further progress in wide‐area and high‐speed communication networks, however, an environment has emerged in which super‐high‐speed service of gigabit‐per‐second order is provided with a long transfer distance. Thus, the window size is limited by the hardware size of the prepared receiver buffer, and the effective throughput is limited. This paper considers this problem and proposes a flow control scheme in which the effective throughput is not restricted by the transfer distance. In the proposed method, the WABT scheme, which is a non‐window‐type flow control, is combined with relay buffering in the network. By applying this method, the effective throughput is not affected by the increase in the transfer distance or the effect of transmission delay in transfer stop/restart by the starting or release of the flow control mechanism. A theoretical analysis is presented in order to derive the basic characteristics of the proposed scheme, and its effectiveness is demonstrated. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 85(12): 112–120, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1146

Planning Models for Wide-Area Communication Network Design with Response-Time-Dependent Offered Traffic

We address an important planning problem occurring in the design of wide-area networks. Specifically, given a proposed or existing network topology and capacities, we determine how much potential t...