• Journal of KIISE:Computer Systems and Theory
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• v.28 no.9
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• pp.442-460
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• 2001

In video-on-demand(VOD) systems it is important to minimize initial latency and memory requirements. The minimization of initial latency enables the system to provide services with short response time, and the minimization of memory requirements enables the system to service more concurrent user requests with the same amount of memory. In VOD systems, since initial latency and memory requirement increase according to the increment of buffer size allocated to user requests, the buffer size allocated to user requests must be minimized. The existing static buffer allocation scheme, however, determines the buffer size based on the assumption that thy system is in fully loaded state. Thus, when the system is in partially loaded state, the scheme allocates user requests unnecessarily large buffers. This paper proposes a dynamics buffer allocation scheme that allocates user requests the minimum buffer size in fully loaded state as well as a partially loaded state. This scheme dynamically determines the buffer size based on the number of user requests in service and the number of user requests arriving while servicing current requests. In addition, through analyses and simulations, this paper validates that the dynamics buffer allocation outperforms the statics buffer allocation in initial latency and the number of concurrent user requests that can be supported. Our simulation results show that, in proportion to the static buffer allocation scheme, the dynamic buffer allocation scheme reduces the average initial latency by 29%~65%, and in a systems having several disks. increases the average number of concurrent user requests by 48%~68%. Our results show that the dynamic buffer allocation scheme significantly improves the performance and reduce the capacity requirements of VOD systems.

• Korean Journal of Human Ecology
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• v.12 no.3
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• pp.337-349
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• 2003

This study was dealt with consumers' attitudes and requests for refunds on the basis of data gathered in 1997 and 2000 and examined factors shaping the differences of the consumers' requesting for refunds and investigated variables influencing the presence or absence of requests for refunds. Research outcomes could be summarized as follows. First there were no differences in consumers' searches for information of refunds, degrees of satisfactions for practices of refunds, knowledges for refunds, consumers' expectation for the permission of refunds between two periods Consumers generally showed more active behaviors for the request for refunds in 2000 than in 1997. In cases of defects, the chance of getting refunds was higher while consumers feel greater needs for refund. Second, consumers perception for the necessity of refund and their expectations for successful outcomes were higher in cases of defects than in the opposite case; consumers were also more active to request for refunds and get more positive responses in the former case. Third, in cases of defects in 1997, as consumers faced the unsatisfactory response for their previous requests for refunds, they did not actively request for refunds. In 2000, requesting for refunds were more active as they were more knowledgeable, actively search for information of refunds before their purchases, and expect more positive outcomes for their requests for refund. On the other hand, in cases of no defects in 1997, consumers showed more active behaviors requesting for refunds as their own professional jobs, owned greater consumer expectation for positive outcomes and showed greater satisfactions for the previous requests of refunds. In the survey of 2000, consumers showed active behaviors requesting for refunds as they were highly educated, gather much information for refund, and showed positive expectations for the possibility of refund.

• IE interfaces
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• v.12 no.4
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• pp.557-566
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• 1999

This paper considers a door-to-door service system in which pickups or deliveries are performed by a trip of a single vehicle. Each customer request specifies the quantity of the load transported, the location, and the time window within which it is to be picked up or delivered. Since the system is demand responsive, i.e., new or emergent requests become available in real-time, the current vehicle route has to be reconstructed to include these requests. In this case, only continuous vehicle tracking enables control over the requests and ensures that the requests are satisfied on time. This paper suggests a pilot pickup/delivery management system integrating a geographic information system(GIS) and a global position system(GPS) to efficiently deal with such a dynamic environment. The GIS offers a way of displaying the vehicle route on digital maps for the region under concerned. Also displayed is the current location of the vehicle obtained from the GPS. A heuristic algorithm is used to dynamically determine the vehicle route. A practical example is provided to show the feasibility of the system.

• The Transactions of the Korea Information Processing Society
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• v.7 no.2S
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• pp.656-665
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• 2000

A critical issue in the performance of a video-on-demand system is the I/O bandwidth required in order to satisfy client requests. Several approaches: batching, bridging, piggybacking are used ot reduce the I/O demand on the video server through sharing. Piggybacking is the policy for altering display rates of requests in progress fro the same object, for the purpose of merging their corresponding I/O streams into a single stream, which can serve the entire group of merged requests. In this paper, we propose a new policy called an adaptive reservation-based piggybacking that dynamically reserves the I/O stream capacity of video server for popular videos according to video server loads to immediately schedule the requests for popular videos. The performance of the proposed policy is evaluated through simulations, and is compared with that of simple piggybacking. As the result, we know that the adaptive reservation-based piggybacking provides better service probability, average waiting time and percentages saving in frames than simple piggybacking.

• English Language & Literature Teaching
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• v.7 no.1
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• pp.51-66
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• 2001

This paper compares different uses of downgraders by Korean English speakers (KES) with those by American English native speakers (AENS) in their requestive e-mail. Three different situations in which social power and distance were controlled were set up to examine and compare the participants' politeness strategies in requestive e-mail. It was found that the KESs' use of downgraders appeared differently from the AENSs' use qualitatively and quantitatively across three situations. The AENSs used downgraders almost three times as more, resulting in a much more mitigated and polite effect in requests. The AENSs' requests were mostly modified by syntactic modifiers, such as aspect, tense, conditional, and consultative devices. On the other hand, the KESs' requests were modified mostly by politeness markers and conditionals in a limited number of requests.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.322-325
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• 2000

In a batch scheduling policy being different from real video system, the requests are not served immediately due to grouping user's requests upon every scheduling points. Such waiting delays by inefficient managements makes an unfair service to users and increases the possibility of higher reneging rates. This paper proposes an adaptive batch scheduling scheme which reduces the average waiting time of user’s requests and reduces the starvation problem for requesters of less popular movies. The proposed scheme selects dynamically multiple videos in given intervals based on the service patterns which reflect the popularity distribution and resource utilizations. Experimental simulation shows that proposed scheme improves about 20-30 percent of average waiting time and reduces significantly the starving requesters comparing with those of conventional methods such as FCFS and MQL.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.1
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• pp.23-34
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• 2010

As the number of user increases according to the improvement of the network, the multi-thread schemes are used to process the service requests of several users who are connected simultaneously. The static thread pool scheme has the problem of occupying a static amount of system resources. On the other hand, the dynamic thread pool scheme can control the number of threads according to the users' requests. However, it has disadvantage that this scheme cannot react to the requests which are larger than the maximum value assigned. In this paper, a web server using a learning-based dynamic thread pool scheme is suggested, which will be running on a server programming of a multi-thread environment. The suggested scheme adds the creation of the threads through the prediction of the next number of periodic requests using Auto Regressive scheme with the web server apache worker MPM (Multi-processing Module). Unlike previous schemes, in order to set the exact number of the necessary threads during the unchanged number of work requests in a certain period, K-Nearest Neighbor algorithm is used to learn the number of threads in advance according to the number of requests. The required number of threads is set by comparing with the previously learned objects. Then, the similar objects are selected to decide the number of the threads according to the request, and they create the threads. In this paper, the response time has decreased by modifying the number of threads dynamically, and the system resources can be used more efficiently by managing the number of threads according to the requests.

• The Journal of Society for e-Business Studies
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• v.20 no.1
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• pp.79-88
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• 2015

Many servers, such as web and database servers, receive a continual stream of requests. The servers should schedule these requests to provide the best services to users. In this paper, a hybrid genetic algorithm is proposed for scheduling divisible requests without interruption in which the objective is to minimize the total stretch. The stretch of a request is the ratio of the amount of time the request spent in the system to its response time. The hybrid genetic algorithm adopts the idea of seed selection and development in order to improve the exploitation and exploration power of genetic algorithms. Extensive computational experiments have been conducted to compare the performance of the hybrid genetic algorithm with that of genetic algorithms.

• Journal of the Korean Home Economics Association
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• v.48 no.3
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• pp.31-41
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• 2010

This study analyzes the difficulties that student teachers, beginning teachers and experienced teachers face in the field of kindergarten, and urgent support requests. The total of participants was 372 of this number, 122 were student teachers, 118 were beginning teachers and 132 were experienced teachers. The results showed the difference in difficulties and the needed support requests among student teachers, beginning teachers and experienced teachers. Student teachers had the difficulty of time management, but beginning teachers and experienced teachers had trouble due to the nonexistence of assistant teachers. Student teachers required teaching strategies for starting relationships with children within responsibility. Beginning teachers and experienced teachers regarded the plan, practice, and evaluation of a program as the most needed support request. Collectively, the results revealed that expansion of the practice period is necessary for student teachers so that they can gain experience with children, parents, and the children's education institution with various opportunities as a learning course.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.54 no.10
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• pp.615-619
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• 2005

Token coherence protocol has many good reasons against snooping/directory-based protocol in terms of latency, bandwidth, and complexity. Token counting easily maintains correctness of the protocol without global ordering of request which is basis of other dominant cache coherence protocols. But this lack of global ordering causes starvation which is not happening in snooping/directory-based protocols. Token coherence protocol solves this problem by providing an emergency mechanism called persistent request. It enforces other processors in the competition (or accessing same shared memory block, to give up their tokens to feed a starving processor. However, as the number of processors grows in a system, the frequency of starvation occurrence increases. In other words, the situation where persistent request occurs becomes too frequent to be emergent. As the frequency of persistent requests increases, not only the cost of each persistent matters since it is based on broadcasting to all processors, but also the increased traffic of persistent requests will saturate the bandwidth of multiprocessor interconnection network. This paper proposes a new request mechanism that defines order of requests to reduce occurrence of persistent requests. This ordering mechanism has been designed to be decentralized since centralized mechanism in both snooping-based protocol and directory-based protocol is one of primary reasons why token coherence protocol has advantage in terms of latency and bandwidth against these two dominant Protocols.