• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권8호
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• pp.2783-2804
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• 2021

In the network function virtualization environment, dynamic changes in network traffic will lead to the dynamic changes of service function chain resource demand, which entails timely dynamic adjustment of service function chain resource configuration. At present, most researches solve this problem through virtual network function migration and link rerouting, and there exist some problems such as long service interruption time, excessive network operation cost and high penalty. This paper proposes a dynamic adjustment method of service function chain resource configuration for the dynamic changes of network traffic. First, a dynamic adjustment request of service function chain is generated according to the prediction of network traffic. Second, a dynamic adjustment strategy of service function chain resource configuration is determined according to substrate network resources. Finally, the resource configuration of a service function chain is pre-adjusted according to the dynamic adjustment strategy. Virtual network functions combination and virtual machine reusing are fully considered in this process. The experimental results show that this method can reduce the influence of service function chain resource configuration dynamic adjustment on quality of service, reduce network operation cost and improve the revenue of service providers.

• 한국수학교육학회지시리즈A:수학교육
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• 제57권4호
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• pp.477-491
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• 2018

In this paper we study in-service teachers' and pre-service teachers' recognition the domain in the problem concerning the continuity of a function. By a questionnaire survey we find out that most of in-service teachers and pre-service teachers are understanding the continuity of a function as explained in high school mathematics textbook, in which the continuity was defined by and focused on comparing the limit with the value of the function. We also notice that this kind of definition for the continuity of a function makes them trouble to figure out whether a function is continuous at an isolated point, and to determine that a given function is continuous on a region by not considering its domain explicitly. Based on these results we made several suggestions to improve for in-service teachers and pre-service teachers to understand the continuity of a function more exactly, including an introduction of a more formal words usage such as 'continuous on a region' in high school classroom.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권2호
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• pp.577-594
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• 2020

Service Function Chaining (SFC) supports services through linking an ordered list of functions. There may be multiple instances of the same function, which provides a challenge to select available instances for all the functions in an SFC and generate a specific Service Function Path (SFP). Aiming to solve the problem of SFP selection, we propose an architecture consisting of distributed SFP algorithm and central control mechanism. Nodes generate distributed routings based on the first function and destination node in each service request. Controller supervises all of the distributed routing tables and modifies paths as required. The architecture is scalable, robust and quickly reacts to failures because of distributed routings. Besides, it enables centralized and direct control of the forwarding behavior with the help of central control mechanism. Simulation results show that distributed routing tables can generate efficient SFP and the average cost is acceptable. Compared with other algorithms, our design has a good performance on average cost of paths and load balancing, and the response delay to service requests is much lower.

• 대한원격탐사학회지
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• 제33권6_2호
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• pp.1119-1137
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• 2017

본 연구는 서울과 경기도 지역 도시숲의 수자원 공급 생태계서비스와 기후완화 생태계서비스를 평가하였다. 생태계서비스를 자연기능기반 서비스, 산림의 자연기능과 인구분포를 고려한 생태계서비스, 산림의 자연기능과 수혜자 분포를 고려한 생태계서비스의 세 가지 서비스로 구분하여 평가하고, 이후 기후변화가 생태계서비스에 미치는 영향을 평가하였다. 평가 결과, 토지피복과 토양 등 자연조건을 반영한 도시림의 수자원 공급서비스의 경우, 경기도가 서울보다 높은 서비스를 제공하는 것으로 나타났으며, 지역별 인구분포를 추가적으로 반영한 서비스 평가에서는 인구가 많은 곳에서 서비스가 높게 나타나는 양상을 보였다. 그러나 도시림의 수자원 수혜자 분포를 추가로 반영한 수자원 공급 생태계서비스 평가 결과는 인구분포를 반영한 서비스 평가 결과와 공간적으로 다르게 나타났다. 같은 수원함양 기능을 가진 지역이라도 인구분포나 물 사용 수혜자의 분포가 많은 지역일수록 높은 서비스 결과가 나타났다. 또한 기후변화가 수자원 공급 생태계에 서비스에 미치는 영향을 평가한 결과, 기후변화에 따른 수자원 공급 서비스는 평균적으로 26%정도 줄어들어 전반적인 수자원 공급 생태계서비스가 낮아지는 경향을 보였다. 기후완화부문의 경우, 산림으로부터 가까운 거리에 있을수록 높은 온도저감 효과가 나타나 산림주변지역에서 높은 기후완화서비스가 나타났으며, 기후 완화 서비스의 수혜자 인구를 고려한 생태계서비스 평가에서는 수혜인구의 밀도가 높은 서울 도심지역에서 높은 서비스가 나타났다. 기후변화에 따른 산림 생장량 변화를 반영하여 산림의 기후완화 생태계서비스의 변화를 평가한 결과, 평균적으로 약 33%의 서비스 감소가 나타났다. 본 연구의 결과는 도시림을 관리하기 위해서 산림청에서 제시하고 있는 공급기능기반의 6가지(자연환경보전, 산지재해방지, 목재생산, 산림휴양, 생활환경보전, 수원함양) 기능구분 외에 서비스를 수혜하는 수요자 기반의 기능 및 서비스가 평가의 필요성을 제시한다. 이는 기존의 산림의 공급기능기반의 평가에서 간과할 수 있는, 자연기능은 낮지만 수혜를 받는 시민들이 많아 높은 서비스 가치를 갖는 산림을 재평가하고 올바른 관리 계획을 수립하는데 기여할 수 있을 것으로 판단된다.

• ETRI Journal
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• 제41권2호
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• pp.207-223
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• 2019

Network function virtualization can significantly improve the flexibility and effectiveness of network appliances via a mapping process called service function chaining. However, the failure of any single virtualized network function causes the breakdown of the entire chain, which results in resource wastage, delays, and significant data loss. Redundancy can be used to protect network appliances; however, when failures occur, it may significantly degrade network efficiency. In addition, it is difficult to efficiently map the primary and backups to optimize the management cost and service reliability without violating the capacity, delay, and reliability constraints, which is referred to as the reliability-aware service chaining mapping problem. In this paper, a mixed integer linear programming formulation is provided to address this problem along with a novel online algorithm that adopts the joint protection redundancy model and novel backup selection scheme. The results show that the proposed algorithm can significantly improve the request acceptance ratio and reduce the consumption of physical resources compared to existing backup algorithms.

• 대한수학회보
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• 제46권4호
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• pp.673-689
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• 2009

We analyze $MAP_1,\;MAP_2$/G/1 finite queues with service scheduling function dependent upon queue lengths. The customers are classified into two types. The arrivals of customers are assumed to be the Markovian Arrival Processes (MAPs). The service order of customers in each buffer is determined by a service scheduling function dependent upon queue lengths. Methods of embedded Markov chain and supplementary variable give us information for queue length of two buffers. Finally, the performance measures such as loss probability and mean waiting time are derived. Some numerical examples also are given with applications in telecommunication networks.

• 한국통신학회논문지
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• 제40권6호
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• pp.1032-1039
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• 2015

서비스 기능 체이닝(SFC: Service function chaining)은 다수의 서비스 기능들을 순차적으로 구성하는 기술이다. 서비스 기능 체이닝에서는 확장성과 fault-tolerant를 위해 다수의 서비스 기능 인스턴스가 필요하며, 네트워크에 인입된 플로우는 다수의 서비스 기능 인스턴스로 적절하게 분배되어야 한다. 따라서 본 논문에서는 각 서비스 기능인스턴스들의 자원을 고려하면서 종단 간 지연시간(latency)을 최소화 할 수 있는 플로우 분배 문제를 정의한다. 또한 GT-ITM 토폴로지 생성 툴을 사용하여 보다 현실적인 네트워크 토폴로지 상에서 시뮬레이션을 수행하고, 그 결과 최적의 플로우 분배 기법이 전체 지연시간을 줄일 수 있음을 확인하였다.

• 기본간호학회지
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• 제23권1호
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• pp.61-72
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• 2016

Purpose: Purpose of this retrospective study was to investigate cognitive function, physical function, and problematic behaviors of elders who attended dementia daycare centers, and to identify reasons why they stopped using the center. Methods: Participants were 176 elders, 60 years or over, attending one of four dementia daycare centers in Incheon. Data were collected from center documents. Results: Mean age was 80.5 years. When admitted to the centers mean scores for the mini-mental status examination, activity of daily living, and instrumental activity of daily living (IADL) were 12.31, 9.53, and 25.09 respectively. Participants received day care service for an average of 17.98 months. The reasons for leaving the center were worsening dementia and health (40.2%), and problematic behaviors (20.1%). Conclusion: Results show that elders began to use day care services when their cognitive function and IADL had declined considerably. As the ultimate goal of dementia daycare service is to delay the worsening of cognitive capability and decreases in activities daily living, the effect of the service can be maximized when the service is provided as early as possible in the course of progressively severe dementia. Active promotion should be exerted in the community to encourage early use of this service.

• 산업경영시스템학회지
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• 제33권3호
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• pp.137-145
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• 2010

The objective of this paper is to evaluate the equilibrium price between PSTN and VoIP telephony services in the case of non-linear utility function. Currently there are two types of wired phone services we are known PSTN (Public Switched Telephone Network) and VoIP (Voice over Internet Protocol). The PSTN telephony which provide high quality service and VoIP which provides relatively low quality service form a vertically differentiated oligopoly. Therefore, the evaluation of the equilibrium price between PSTN and VoIP services is very important to wired phone service providers. The equilibrium price depends on the state of the service cost function has been proved different value. This paper was evaluated each equilibrium price for the state of the linear cost function and non-linear cost function. Subsequently, this paper analyzed the demand of both services and the equilibrium profit which can maximize the profit of both service providers.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.121-124
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• 2003

The conventional CNC(Computerized Numerical Controller) of machine tool, which is dependent to CNC maker, was a closed architecture type. Therefore, it is impossible to implement a special user-define function to CNC. But recently, CNC is changed to OAC(Open Architecture Controller) type increasingly and the general function of CNC can be upgrade efficiently. This paper describes web service application for remote monitoring regarding the faults or machine tool with open architecture CNC. The major faults of CNC machine tool can be defined to the operational faults to be charged over 70%. Those faults are unpredictable because of being occurred without any warning. To generalize the fault diagnosis efficiently. two diagnosis models such as SF(Switching Function) and SSF(Step Switching Function) are proposed and the function of fault diagnosis is implemented to internal function of OAC. Also, to service remotely the faults of CNC machine tool. the suitable web environment is proposed and practical function is programmed to evaluate its operation on web.