• Journal of Communications and Networks
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• v.10 no.1
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• pp.79-88
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• 2008

In this paper, we propose efficient peer assignment algorithms for low-latency transmission of scalable coded images in peer-to-peer networks, in which peers may dynamically join and leave the networks. The objective of our algorithm is to minimize the transmission time of a requested image that is scalable coded. When an image is scalable coded in different bit rates, the bit stream encoded in a lower bit rate is a prefix subset of the one encoded in a higher bit rate. Therefore, a peer with the same requested image coded in any bit rate, even when it is different from the requested rate, may work as a supplying peer. As a result, when a scalable coded image is requested, more supplying peers can be found in peer-to-peer networks to help with the transfer. However, the set of supplying peers is not static during transmission, as the peers in this set may leave the network or finish their transmission at different times. The proposed peer assignment algorithms have taken into account the above constraints. In this paper, we first prove the existence of an optimal peer assignment solution for a simple identity permutation function, and then formulate peer assignment with this identity permutation as a mixed-integer programming problem. Next, we discuss how to address the problem of dynamic peer departures during image transmission. Finally, we carry out experiments to evaluate the performance of proposed peer assignment algorithms.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.5
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• pp.709-735
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• 2010

The reciprocal virtue of peer-to-peer networking has stimulated an explosion of peer population and service capacity, ensuring rapid content distribution in peer-to-peer networks. Critical issues such as peer churn, free riding, and skewed workload significantly affect performance results such as service agility, fairness, and resource utilization. To resolve these problems systematically, this study proposes a peer assignment scheme that supports fair peer-to-peer file sharing applications. The proposed scheme exploits the peer duality of both server-oriented peer capacity and client-oriented peer contribution. Accordingly, the system server can prioritize download requests and appropriately assign server peers to uploading file objects. Several functional extensions, including peer substitution and elimination, bandwidth adjustment, and distributed modification, help cope with subtle situations of service starvation and download blocking, and hence make the system design robust and amenable. Simulation results show this design is examined under both centralized and distributed peer-to-peer environments. Performance results confirm that the proposed mechanisms are simple but effective in maintaining service agility and fairness, without loss of overall service capacity in peer-to-peer files sharing systems.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.6
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• pp.2543-2547
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• 2011

This paper suggests a new method for team-based learning which is focusing on the individual job assignment to solve the possible problems of free riders, dysfunctional conflicts, and hostility among students. Especially, it examines that if a method using job assignment could reduce the adverse effects of peer evaluation. This study was executed during one semester. Each team was organized with seven members and an independent job among seven different jobs was assigned to each member. At the end of the semester, it was examined that if individual job assignment had solved the possible problems of free riders, dysfunctional conflicts, and hostility among students. Finally, this study found that a new method of team-based learning using a job assignment lessened a problem of free riders, and reduced dysfunctional conflicts and hostility among students comparing with the peer evaluation method. The suggested method in this paper, which focuses on the job assignment of team project, could improve the efficiency of team-based learning in education course.

• Journal of Communications and Networks
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• v.12 no.3
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• pp.209-215
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• 2010

In an asymmetrical speed channel environment like asymmetric digital subscriber line, the up-link bandwidth is normally smaller than the down-link bandwidth, which will lead to extremely low utilization of down-link bandwidth when current P2P video transmission is applied. To overcome this, a new fast P2P video transmission method applied in an asymmetrical speed channel environment is proposed in this paper. On the basis of the many-to-one concept, the proposed method uses a new multipeer aggregation technique to enhance the utilization of down-link bandwidth. In addition, an adaptive peer assignment algorithm is also introduced in order to minimize the overall transmission time. Experimental results show that by using our proposed method, the utilization of down-link bandwidth is significantly improved, and the overall transmission time is greatly reduced.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.11
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• pp.5455-5475
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• 2016

In this article, we model the distributed relay assignment network as a many-to-one matching market with peer effects. We discuss two scenarios for throughput optimization of relay networks: the scenario of aggregate throughput optimization and the scenario of fairness performance optimization. For the first scenario, we propose a Mutual Benefit-based Deferred Acceptance (MBDA) algorithm to increase the aggregate network throughput. For the second scenario, instead of using the alternative matching scheme, a non-substitution matching algorithm (NSA) is designed to solve the fairness problem. The NSA improves the fairness performance. We prove that both two algorithms converge to a globally stable matching, and discuss the practical implementation. Simulation results show that the performance of MBDA algorithm outperforms existing schemes and is almost the same with the optimal solution in terms of aggregate throughput. Meanwhile, the proposed NSA improves fairness as the scale of the relay network expands.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.12
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• pp.5633-5638
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• 2011

Kim(2011) showed that the team-based teaching method which is focusing on the individual job assignment solves the backlash effects of peer-evaluation method and suggested that it should be studied if the job assignment teaching method does not worsen the learning outcomes[1]. To analyse the learning outcomes of the job assignment teaching method is the purpose of this paper. This paper evaluates the improvement of the learning outcomes which are resulted from a variance of education style that each member of project team was given his specific task. Firstly, all the students evaluate a learning satisfaction and quality of outcomes by themselves. Secondly, an instructor and some professionals evaluate all the outputs. The results showed that the learning outcomes evaluated by students and instructors are improved significantly. The suggested method in this paper, which focuses on the job assignment of team project, could improve the learning outcomes of team project in engineering education.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.5
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• pp.565-573
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• 2016

Wi-Fi Direct standard technology(Wi-Fi Peer to Peer Technical Specifications v1.2, 2010) was designed for allowing peer to peer communication between two or more devices and various products which have been currently manufactured such as smart phone and smart TV have already provided this technical function. In this technology the role of Coordinator in Wi-Fi infrastructure would be matched to GO(Group Owner) which needs relatively high energy resource and computation power due to the high probability for allowing 3rd-party connection, however, the current standard specification would be limited in terms of energy distribution because it has not included a process to determine the role of GO. To address above problem, this paper classified considerable parameters into the general parameters for the physicality of devices and the specific parameters for considering the role position depending on use-case scenario, and proposed a new method called DIVA to help efficiently determining GO role from the member devices of Wi-Fi Direct network. Furthermore the effect of this mechanism was proved via simulation-based experiments.

• Journal of Labour Economics
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• v.33 no.1
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• pp.1-30
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• 2010

Using the College Scholastic Ability Test of year 1995, the paper investigates effects of classroom peers on a student's test scores. It exploits exogenous assignment of students across different classrooms within a school under the leveling policy in 1990s. The empirical results reveal strong impacts of peers on individual students. Negative effects of low-performing peers exceed positive effects of high-performing peers. Such a structure of peer interactions has important implications for ability grouping vs. mixing debates in Korea.

• Journal of Labour Economics
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• v.39 no.3
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• pp.75-97
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• 2016

This paper estimates the peer effect of how improving the under-performing students can affect the academic performance of other students, focusing on the ratio of students more than proficient. We take advantage of the regression discontinuity design of the policy assignment rule of School-for-Improvement (SFI), which targeted the under-performing schools as an identification strategy. The estimation results from the 2009-2010 NAEA (National Assessment of Educational Achievement) reveal that the decrease of the ratio of under-performing students tends to increase the ratio of excellent or proficient students at around the policy cutoff. The finding turns out to be robust to various falsification tests.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4C
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• pp.451-457
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• 2006

A peer-to-peer(P2P) network is inherently vulnerable to malicious attacks from participating peers because of its open, flat, and autonomous nature. This paper addresses the problem of effectively defending from active attacks of malicious peers at bootstrapping phase and at online phase, respectively. We propose a secure membership handling protocol to protect the assignment of ID related things to a newly joining peer with the aid of a trusted entity in the network. The trusted entities are only consulted when new peers are joining and are otherwise uninvolved in the actions of the P2P networks. For the attacks in online phase, we present a novel message structure applied to each message transmitted on the P2P overlay. It facilitates the detection of message alteration, replay attack and a message with wrong information. Taken together, the proposed techniques deter malicious peers from cheating and encourage good peers to obey the protocol of the network. The techniques assume a basic P2P overlay network model, which is generic enough to encompass a large class of well-known P2P networks, either unstructured or not.