Kwang Sik Chung

An Architecture for Adaptive Mobile Learning

In this paper, we present an adaptive mobile learning system that helps users study learning materials anytime anywhere with handheld computers such as PDAs. The theme of this research is to demonstrate the synergetic effects of mobility and adaptivity that are contextualized in a learning environment. Our system considers the information about the cognitive load that a learner is experiencing and learning contents are adaptively presented based on the cognitive and competency attributes of learners. We experimented our system against elementary school students and the results indicated that not only mobility made it possible for learners to study learning materials conveniently, but adaptively providing contents to users based on their cognitive traits enhanced the learning process greatly

VM Migration for Fault Tolerance in Spot Instance Based Cloud Computing

The cloud computing is a computing paradigm that users can rent computing resources from service providers as much as they require. A spot instance in cloud computing helps a user to utilize resources with less expensive cost, even if it is unreliable. When a user performs tasks with unreliable spot instances, failures inevitably lead to the delay of task completion time and cause a seriously deterioration in the QoS of users. To solve the problem, we propose the VM migration scheme to reduce the job waiting time. And in this scheme we use our previously proposed checkpointing method. When a running instance occurs the out-of-bid situation (failure), the VM on the failed instance is to a new instance. Our proposed VM migration scheme reduces the rollback time and the task waiting time when an instance occur the out-of-bid situation. The simulation results show that our scheme achieves performance improvements in the task execution time of 68.94%, 68.61%, and 46.35% compared with the hour-boundary checkpointing scheme, the rising edge-driven checkpointing scheme, and our previously proposed checkpointing scheme., respectively Further, our scheme outperforms the existing schemes in terms of the reduction the total costs per spot instances for a user’s bid.

A gossip-based mutual exclusion algorithm for cloud environments

Mutual exclusion is a salient feature in distributed computing systems whereby concurrent access of processors to a shared resource is granted in a mutually exclusive manner. The primary aim of this study is to investigate the use of a gossip protocol to a mutual exclusion algorithm to cope with scalability and fault-tolerance problems which are fundamental issues for cloud computing systems. In this paper we present a gossip-based mutual exclusion algorithm for cloud computing systems with dynamic membership behavior. The correctness proof of the algorithm is provided. The amortized message complexity of our algorithm is O (n ), where n is the number of nodes. Simulation results show that our proposed algorithm is attractive regarding dynamic membership behavior.

An unstructured termination detection algorithm using gossip in cloud computing environments

Determining termination in dynamic environments is hard due to node joining and leaving. In previous studies on termination detection, some structures, such as spanning tree or computational tree, are used. In this work, we present an unstructured termination detection algorithm, which uses a gossip based scheme to cope with scalability and fault-tolerance issues. This approach allows the algorithm not to maintain specific structures even when nodes join and leave during runtime. These dynamic behaviors are prevalent in cloud computing environments and little attention has been paid by existing approaches. To measure the complexity of our proposed algorithm, a new metric, self-centered message complexity is used. Our evaluation over scalable settings shows that an unstructured approach has a significant merit to solve scalability and fault-tolerance problems with lower message complexity over existing algorithms.

An efficient string searching algorithm based on vowel occurrence pattern

String searching algorithm is used to determine whether a word, a statement and a phrase exists in newspaper article, books, web pages or not. Especially as the volume of web pages and documentation increases, time and cost of searching a pattern increases. In this paper, we consider the characteristics of English alphabets combination in a pattern and a text(frequency and position of vowels in a pattern and a text), and propose new efficient string searching algorithm based on vowel composition structure of pattern and text. If a pattern has two or more vowels, proposed vowel-based string searching algorithm is more efficient at the both case of best matching case and worst matching case. Especially, a pattern’s length does not affect performance of proposed vowel-based string searching algorithm. Only a pattern’s location in a text can affect running time of algorithm. Proposed vowel-based string searching algorithm can avoid un-matching vowels in a text and un-necessary comparison between a pattern and a text. Therefore in reality, vowel-based string searching algorithm is usefully and effectively applicable to string searching function of a pattern and a text.

The Idle Mobile Resource Discovery and Management Scheme in Mobile Grid Computing Using IP-paging

In this paper, we tried to enable a mobile device as a resource to access to the grid network. By improved internet technique, the use of mobile devices is rapidly increased. And some researches in grid computing tried to combine grid computing with mobile devices. However, according to properties of mobile environments, mobile devices have many considerations, such as mobility management, disconnected operation, device heterogeneity, service discovery, resource sharing, security and so on. To conquest these problems, there are two trends for mobile grid computing: a proxy-based mobile grid architecture and an agent-based mobile grid architecture. We focused on a proxy-based mobile grid architecture with IP-paging, which easily manage idle mobile devices and grid resource status information. In result, to support mobile grid services, we propose the IP-paging scheme based on the mobile grid computing framework. Moreover, we have discussed some research issues: location tracking using IP-paging, limited power using grid paging cache, and service migration using reserved resource. And, we also propose a mobile proxy and paging agent prototype. Keywords-component; Mobile Grid Computing, IP-Paging, Active/Idle state, Power consumption

Byzantine-resilient dual gossip membership management in clouds

In this paper, we present an effective and efficient Byzantine-resilient dual membership management technique in cloud environments, in which nodes are prone to churn and the network topology is not fully connected. Our method is based on unstructured message communication model, namely a gossip protocol that is able to handle the dynamic behavior of nodes properly in the system. We argue that due to the presence of malicious Byzantine nodes, existing membership management mechanisms are not suitable for preserving uniformity of random sampling. Therefore, we propose a new membership management mechanism using gossip with social membership information. The proposed membership management scheme maintains not only neighbor nodes in a social graph, but also Byzantine nodes in a local data structure. The results show that our dual membership management effectively deals with Byzantine nodes, requiring only n

Effective low-latency k-nearest neighbor search via wireless data broadcast

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