• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.46-54
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• 2018

The Internet of Things (IoT) is an environment in which various devices provide services to users through communications. Because of the nature of the IoT, data are stored and distributed in heterogeneous information systems. In this situation, IoT end applications should be able to access data without having information on where the data are or what the type of storage is. This mechanism is called Service Discovery (SD). However, some problems arise, since the current SD architectures search for data in physical devices. First, turnaround time increases from searching for services based on physical location. Second, there is a need for a data structure to manage devices and services separately. These increase the administrator's service configuration complexity. As a result, the device-oriented SD structure is not suitable to the IoT. Therefore, we propose an SD structure called Name-based Service-centric Service Discovery (NSSD). NSSD provides name-based centralized SD and uses the IoT edge gateway as a cache server to speed up service discovery. Simulation results show that NSSD provides about twice the improvement in average turnaround time, compared to existing domain name system and distributed hash table SD architectures.

• Journal of Broadcast Engineering
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• v.15 no.3
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• pp.407-413
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• 2010

In DCA (Dynamic Channel Allocation) scheme of uplink cellular system appling a frequency reuse factor of one, when a new call requests a channel, the new call will be blocked if its SINR (Carrier to Noise and Interference Ratio) is less than the required SINR or there is no available channel. The additional channel allocation for the blocked new call can be performed with channel borrowing in the adjacent cells. The channel borrowing causes the CCI (Co-Channel Interference), thus the SINR of the existing calls is deteriorated and the channel reallocation for the existing calls is required. As a result, the channel borrowing leads to a complex calculation so that it is a NP-hard problem. Therefore, to overcome the problem, we propose a novel Group Search-based DCA scheme which decreases the number of the blocked new calls and then reduces the number of the channel reallocation by the channel borrowing for the blocked new calls. The proposed scheme searches the all channels in a group of the adjacent cells and home cell at the same time in order to minimizes the number of the blocked new calls. The simulation results show that proposed Group Search-based DCA scheme provides better new call blocking probability and system throughput than the existing Single Search-based DCA scheme which searches only the channels in home cell.

• Journal of Broadcast Engineering
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• v.18 no.2
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• pp.215-224
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• 2013

With the rising popularity of smart-phones, the supply of Internet protocol television is largely increased and it causes the wireless communication network load to be increased. To overcome such an overloading problem, 3GPP is now working on the standardization of MBMS since LTE Release 6 specification. MBMS has good performance in bandwidth efficiency by sharing the same bandwidth with the mulitple MBMS users having the same content. According to the proposed algorithm, in heterogeneous networks having a dispersed Single-cell MBMS where 3GPP network and Wi-Fi network are mixed, if the number of MBMS users, who are belonging to cells supporting a dispersed Single-cell MBMS, is more than a specified threshold, the MBMS priority policy is operated. Otherwise, the Wi-Fi priority policy is executed. As the simulation results show both the increase of total available bandwidth ratio and the decrease of network usage cost, it is confirmed that the proposed scheme allows the network efficiency to be maximized.

• Journal of KIISE:Computer Systems and Theory
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• v.30 no.12
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• pp.708-713
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• 2003

For many years clustered heterogeneous web server architecture has been formed on the internet because the explosive internet services and the various quality of requests. The critical point in cluster environment is the mapping schemes of request to server. and recently this is the main issue of internet architecture. The topic of previous mapping methods is to assign equal loads to servers in cluster using the number of requests. But recent growth of various services makes it hard to depend on simple load balancing to satisfy appropriate latency. So mapping based on requested content to decrease response time and to increase cache hit rates on entire servers - so called “content-based” mapping is highly valuated on the internet recently. This paper proposes Prioritized Highest Random Weight mapping(PHRW mapping) that improves content-based mapping to properly fit in the heterogeneous environment. This mapping scheme that assigns requests to the servers with priority, is very effective on heterogeneous web server cluster, especially effective on decreasing latency of reactive data service which has limit on latency. This paper have proved through algorithm and simulation that proposed PHRW mapping show higher-performance by decrease in latency.

• The KIPS Transactions:PartD
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• v.10D no.7
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• pp.1067-1076
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• 2003

Database sharing system (DSS) refers to a system for high performance transaction processing. In DSS, the processing nodes are locally coupled via a high speed network and share a common database at the disk level. Each node has a local memory and a separate copy of operating system. To reduce the number of disk accesses, the node caches database pages in its local memory buffer. In this paper, we propose a dynamic transaction routing algorithm to balance the load of each node in the DSS. The proposed algorithm is novel in the sense that it can support node-specific locality of reference by utilizing the primary copy authority assigned to each node; hence, it can achieve better cache hit ratios and thus fewer disk I/Os. Furthermore, the proposed algorithm avoids a specific node being overloaded by considering the current workload of each node. To evaluate the performance of the proposed algorithm, we develop a simulation model of the DSS, and then analyze the simulation results. The results show that the proposed algorithm outperforms the existing algorithms in the transaction processing rate. Especially the proposed algorithm shows better performance when the number of concurrently executed transactions is high and the data page access patterns of the transactions are not equally distributed.

• Journal of KIISE:Information Networking
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• v.32 no.1
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• pp.89-99
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• 2005

Advances of Internet and rC accelerate distribution and sharing of information, which make P2P(Peer-to-Peer) computing paradigm appear P2P computing Paradigm is the computing paradigm that shares computing resources and services between users directly. A fundamental problem that confronts Peer-to-Peer applications is the efficient location of the node that stoles a desired item. P2P systems treat the majority of their components as equivalent. This purist philosophy is useful from an academic standpoint, since it simplifies algorithmic analysis. In reality, however, some peers are more equal than others. We propose the P2P protocol considering differences of capabilities of computers, which is ignored in previous researches. And we examine the possibility and applications of the protocol. Simulating the Magic Square, we estimate the performances of the protocol with the number of hop and network round time. Finally, we analyze the performance of the protocol with the numerical formula. We call our p2p protocol the Magic Square. Although the numbers that magic square contains have no meaning, the sum of the numbers in magic square is same in each row, column, and main diagonal. The design goals of our p2p protocol are similar query response time and query path length between request peer and response peer, although the network information stored in each peer is not important.

• Journal of Korean Society of Transportation
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• v.21 no.2
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• pp.119-130
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• 2003

SP data have been widely used in assessing new transport policies and transport related plans. However, one of criticisms of using SP is that respondents may show different reaction between hypothetical experiments and real life. In order to overcome the problem, combination of SP and RP data has been suggested and the combined methods have been being developed. The purpose of this paper is to suggest a new SP and RP combined method using error component method and to verify the method. The error component method decomposes IID extreme value error into non-IID error component(s) and an IID error component. The method estimates both of component parameters and utility parameters in order to obtain relative variance of SP data and RP data. The artificial SP and RP data was created by using simulation and used for the analysis, and the estimation results of the error component method were compared with those of existing SP and RP combined methods. The results show that regardless of data size, the parameters of the error component method models are similar to those assumed parameters much more than those of the existing SP and RP combined models, indicating usefulness of the error component method. Also the values of time for error component method are more similar to those assumed values than those of the existing combined models. Therefore, we can conclude that the error component method is useful in combining SP and RP data and more efficient than the existing methods.

• Journal of Internet Computing and Services
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• v.10 no.5
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• pp.41-47
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• 2009

Routing through a backbone, which is responsible for performing and managing multipoint communication, reduces the communication overhead and overall energy consumption in wireless sensor networks. However, the backbone nodes will need extra functionality and therefore consume more energy compared to the other nodes. The power consumption imbalance among sensor nodes may cause a network partition and failures where the transmission from some sensors to the sink node could be blocked. Hence optimal construction of the backbone is one of the pivotal problems in sensor network applications and can drastically affect the network's communication energy dissipation. In this paper a distributed algorithm is proposed to generate backbone trees through robust multi-hop clusters in wireless sensor networks. The main objective is to form a properly designed backbone through multi-hop clusters by considering energy level and degree of each node. Our improved cluster head selection method ensures that energy is consumed evenly among the nodes in the network, thereby increasing the network lifetime. Comprehensive computer simulations have indicated that the newly proposed scheme gives approximately 10.36% and 24.05% improvements in the performances related to the residual energy level and the degree of the cluster heads respectively and also prolongs the network lifetime.

• Proceedings of the Korean Information Science Society Conference
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• 2006.10d
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• pp.24-29
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• 2006

본 논문에서는 광대역 통신 방송 융합 서비스 제공을 고려한 WDM 메트로 링 망을 위한 매체 접근 제어(Medium Access Control; MAC) 프로토콜의 성능을 분석한다. 현재 인터넷은 통신 방송 융합 망으로 진화하고 있으며 다양한 트래픽 특성을 갖는 서비스가 액세스 망에서 메트로 망으로 유입되고 있다. 그러나 기존 메트로 망의 MAC 프로토콜은 이러한 망 환경 변화를 고려하지 않고 단순하고 동일한 트래픽만을 고려하여 성능을 분석하였다. 따라서 본 논문에서는 메트로 링에 연결된 액세스 노드의 입력 트래픽을 Self-Similar와 Poisson 트래픽으로 분류하여 기존 MAC 프로토콜의 성능을 분석하고 평가한다. 메트로 링 망에 연결된 액세스 노드는 이 두 종류의 트래픽 중에서 하나를 망에 유입하며 채널을 공유하는 노드 수에 따라서 다양한 트래픽 환경이 고려된다. WDM 메트로 링망의 기본 MAC 프로토콜은 CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance)이며, 패킷을 빈 슬롯에 전송하고 송신지에서 패킷을 제거하는 SS (Source-Stripping) 기반으로 운용된다. 본 논문에서는 SS 방식으로 생성된 빈 슬롯을 바로 패킷 전송에 이용하는 방식과 그렇지 않은 방식을 각각 1-Persistent와 non-Persistent로 분류하고 MAC 프로토콜을 분석하여 기존 방식의 장 단점을 비교한다. 또한 전송 공정성과 처리율을 같이 고려하여 적용할 수 있는 확률 기반 p-Persistent MAC 프로토콜도 분석하였으며 시뮬레이션을 통하여 각 프로토콜을 노드 처리율, 전송 지연, 패킷 손실률, 전송 공정성 관점에서 비교하고 평가한다.y 수행을 여러 서버로 분산처리하게 함으로써 성능에 대한 신뢰성을 향상 시킬 수 있는 Load Balancing System을 제안한다.할 때 가장 효과적인 라우팅 프로토콜이라고 할 수 있다.iRNA 상의 의존관계를 분석할 수 있었다.수안보 등 지역에서 나타난다 이러한 이상대 주변에는 대개 온천이 발달되어 있었거나 새로 개발되어 있는 곳이다. 온천에 이용하고 있는 시추공의 자료는 배제하였으나 온천이응으로 직접적으로 영향을 받지 않은 시추공의 자료는 사용하였다 이러한 온천 주변 지역이라 하더라도 실제는 온천의 pumping 으로 인한 대류현상으로 주변 일대의 온도를 올려놓았기 때문에 비교적 높은 지열류량 값을 보인다. 한편 한반도 남동부 일대는 이번 추가된 자료에 의해 새로운 지열류량 분포 변화가 나타났다 강원 북부 오색온천지역 부근에서 높은 지열류량 분포를 보이며 또한 우리나라 대단층 중의 하나인 양산단층과 같은 방향으로 발달한 밀양단층, 모량단층, 동래단층 등 주변부로 NNE-SSW 방향의 지열류량 이상대가 발달한다. 이것으로 볼 때 지열류량은 지질구조와 무관하지 않음을 파악할 수 있다. 특히 이러한 단층대 주변은 지열수의 순환이 깊은 심도까지 가능하므로 이러한 대류현상으로 지표부근까지 높은 지온 전달이 되어 나타나는 것으로 판단된다.의 안정된 방사성표지효율을 보였다. $^{99m}Tc$-transferrin을 이용한 감염영상을 성공적으로 얻을 수 있었으며, $^{67}Ga$-citrate 영상과 비교하여 더 빠른 시간 안에 우수한 영상을 얻을 수 있었다. 그러므로 $^{99m}Tc$-transierrin이 감염 병소의 영상진단에 사용될 수 있을 것으로 기대된

• Journal of Internet Computing and Services
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• v.21 no.5
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• pp.1-7
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• 2020

Deep neural networks(DNN), which are used as approximation functions in reinforcement learning (RN), theoretically can be attributed to realistic results. In empirical benchmark works, time difference learning (TD) shows better results than Monte-Carlo learning (MC). However, among some previous works show that MC is better than TD when the reward is very rare or delayed. Also, another recent research shows when the information observed by the agent from the environment is partial on complex control works, it indicates that the MC prediction is superior to the TD-based methods. Most of these environments can be regarded as 5-step Q-learning or 20-step Q-learning, where the experiment continues without long roll-outs for alleviating reduce performance degradation. In other words, for networks with a noise, a representative network that is regardless of the controlled roll-outs, it is better to learn MC, which is robust to noisy rewards than TD, or almost identical to MC. These studies provide a break with that TD is better than MC. These recent research results show that the way combining MC and TD is better than the theoretical one. Therefore, in this study, based on the results shown in previous studies, we attempt to exploit a random balance with a mixture of TD and MC in RL without any complicated formulas by rewards used in those studies do. Compared to the DQN using the MC and TD random mixture and the well-known DQN using only the TD-based learning, we demonstrate that a well-performed TD learning are also granted special favor of the mixture of TD and MC through an experiments in OpenAI Gym.