Proceedings of the 5th international conference on Parallel and Distributed Computing: applications and Technologies

Content distribution networks (CDNs) using storage clouds have recently started to emerge. Compared to traditional CDNs, storage cloud-based CDNs have the advantage of cost effectively offering hosting services to Web content providers without owning infrastructure. However, existing work on replica placement in CDNs does not readily apply in the cloud. In this paper, we investigated the joint problem of building distribution paths and placing Web server replicas in cloud CDNs to minimize the cost incurred on the CDN providers while satisfying QoS requirements for user requests. We formulate the cost optimization problem with accurate cost models and QoS requirements and show that the monthly cost can be as low as 2.62 US Dollars for a small Web site. We develop a suite of offline, online-static and online-dynamic heuristic algorithms that take as input network topology and work load information such as user location and request rates. We then evaluate the heuristics via Web trace-based simulation, and show that our heuristics behave very close to optimal under various network conditions.

Intra-cloud lightning: Building CDNs in the cloud

Cloud computing is a new technology and it is becoming popular day by day because of its great features. In this technology almost everything like hardware, software and platform are provided as a service. These services are charged from users on the pay-per-use bases. A cloud provider in cloud computing provides services on the basis of clients' requests. An important issue in cloud computing is the scheduling of users' requests means how to allocate resources to these requests, so that the requested tasks can be completed in a minimum time according to the user defined time. A good scheduling technique also helps in efficient utilization of the resources. Many scheduling algorithms have been researched like Min-Min, Max-Min, X-Sufferage, Genetic Algorithm, Particle Swarm Optimization etc. In this paper the three scheduling techniques Min-Min, Max-Min and Genetic Algorithm have been discussed and performance metrics of Min-Min and Max-Min have been shown. The performance of the standard Genetic Algorithm and the proposed Improved Genetic Algorithm have been checked against the sample data. A new scheduling idea is also proposed in which Min-Min and Max-Min can be combined in Genetic Algorithm.

Scheduling using improved genetic algorithm in cloud computing for independent tasks

Traditionally, higher education institutions have developed orientation programs that are designed to help students make a successful transition to college. Now, considering this flow of virtual students, universities offering distance learning programs have to design orientation programs suited for the students that will take distance courses. This article introduces the issues to be considered in designing an orientation for students in online programs and presents the strategies being used currently in some Internet-based courses. Orientation for online courses serve the same objectives as orientation for college, in the sense that it can facilitate academic and social interactions, increase student involvement, enhance the sense of belonging to a virtual learning community, and help retention.

Student Orientations for Online Programs

A dynamic replica management strategy in data grid

The Replica Placement Problem (RPP) aims at creating a set of duplicated data objects across the nodes of a distributed system in order to optimize certain criteria. Typically, RPP formulations fall into two categories: static and dynamic. The first assumes that access statistics are estimated in advance and remain static, and, therefore, a one-time replica distribution is sufficient (IRPP). In contrast, dynamic methods change the replicas in the network potentially upon every request. This paper proposes an alternative technique, named Continuous Replica Placement Problem (CRPP), which falls between the two extreme approaches. CRPP can be defined as: Given an already implemented replication scheme and estimated access statistics for the next time period, define a new replication scheme, subject to optimization criteria and constraints. As we show in the problem formulation, CRPP is different in that the existing heuristics in the literature cannot be used either statically or dynamically to solve the problem. In fact, even with the most careful design, their performance will be inferior since CRPP embeds a scheduling problem to facilitate the proposed mechanism. We provide insight on the intricacies of CRPP and propose various heuristics.

Continuous Replica Placement schemes in distributed systems

Embedded applications can be structured in terms of mobile agents that are flexibly installed on available nodes. In wireless systems, such nodes typically have limited battery and memory resources; therefore it is important to place agents judiciously. In this paper we tackle the problem of placing a newcomer agent in such a system. The problem has two main components. First, enough memory space must be found or created at some node to place the agent. Second, the placement should be energy efficient. We present heuristics for tackling these two goals in a stepwise fashion, as well as a branch and bound method for achieving both goals at the same time. Our algorithms are centralized assuming a single entry point through which agents are injected into the system, with adequate knowledge of the system state and enough resources to run the proposed algorithms. The algorithms are evaluated under different simulated scenarios, and the tradeoffs across the two metrics (space, energy) are identified.

Agent placement in wireless embedded systems: Memory space and energy optimizations

This paper describes middleware-level support for agent mobility, targeted at hierarchically structured wireless sensor and actuator network applications. Agent mobility enables a dynamic deployment and adaptation of the application on top of the wireless network at runtime, while allowing the middleware to optimize the placement of agents, e.g., to reduce wireless network traffic, transparently to the application programmer. The paper presents the design of the mechanisms and protocols employed to instantiate agents on nodes and to move agents between nodes. It also gives an evaluation of a middleware prototype running on Imote2 nodes that communicate over ZigBee. The results show that our implementation is reasonably efficient and fast enough to support the envisioned functionality on top of a commodity multi-hop wireless technology. Our work is to a large extent platform-neutral, thus it can inform the design of other systems that adopt a hierarchical structuring of mobile components.

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Middleware mechanisms for agent mobility in wireless sensor and actuator networks

Given two replication schemes Xold and Xnew, the replica transfer scheduling problem (RTSP) aims at reaching Xnew, starting from Xold, with minimal implementation cost. In this paper we generalize the problem description to include special cases, where deadlocks can occur while in the process of implementing Xnew. We address this impediment by introducing artificial (dummy) transfers. We then prove that RTSP-decision is NP-complete and propose two kinds of heuristics. The first attempts to replace dummy transfers with valid ones, while the second minimizes the implementation cost. Experimental evaluation of the algorithms illustrates the merits of our approach.

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Implementing Replica Placements: Feasibility and Cost Minimization

In this paper, we present the methodology and results derived from a distance learning programme offered by a higher education institute to adults. Computer Science and interdisciplinary courses are offered through a Web-based Learning Management System (LMS). Administrative, technical and pedagogical issues are considered systemically and a methodology is developed taking into consideration the group of learners, appropriate learning methods, assessment methods, social and economical aspects concerning distance learning and the technological infrastructure in place. An assessment procedure is reached and carried out thoroughly involving all components of the programme. Results depict success in certain aspects of the overall programme, as well as suggestions for enhancement of the distance learning setting.

Petros Lampsas

Papers

Continuous Replica Placement schemes in distributed systems

Agent placement in wireless embedded systems: Memory space and energy optimizations

Middleware mechanisms for agent mobility in wireless sensor and actuator networks

Implementing Replica Placements: Feasibility and Cost Minimization

Adult distance learning using a web-based learning management system: methodology and results