• Journal of KIISE:Information Networking
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• v.35 no.2
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• pp.99-111
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• 2008

In recent years, the needs for WLANs(Wireless Local Area Networks) technology which can access to Internet anywhere have been dramatically increased particularly in SOHO(Small Office Home Office) and Hot Spot. However, unlike wired networks, there are some unique characteristics of wireless networks. These characteristics include the burst packet losses due to unreliable wireless channel. Note that burst packet losses, which occur when the distance between the wireless station and the AP(Access Point) increase or when obstacles move temporarily between the station and AP, are very frequent in 802.11 networks. Conversely, due to burst packet losses, the performance of 802.11 networks are not always as sufficient as the current application require, particularly when they use TCP at the transport layer. The high packet loss rate over wireless links can trigger unnecessary execution of TCP congestion control algorithm, resulting in performance degradation. In order to overcome the limitations of WLANs environment, MAC-layer LDA(Loss Differentiation Algorithm)has been proposed. MAC-layer LDA prevents TCP's timeout by increasing CRD(Consecutive Retry Duration) higher than burst packet loss duration. However, in the wireless channel with high packet loss rate, MAC-layer LDA does not work well because of two reason: (a) If the CRD is lower than burst packet loss duration due to the limited increase of retry limit, end-to-end performance is degraded. (b) energy of mobile device and bandwidth utilization in the wireless link are wasted unnecessarily by Reducing the drainage speed of the network buffer due to the increase of CRD. In this paper, we propose a new retransmission module based on Cross-layer approach, called BLD(Burst Loss Detection) module, to solve the limitation of previous link layer retransmission schemes. BLD module's algorithm is retransmission mechanism at IEEE 802.11 networks and performs retransmission based on the interaction between retransmission mechanisms of the MAC layer and TCP. From the simulation by using ns-2(Network Simulator), we could see more improved TCP throughput and energy efficiency with the proposed scheme than previous mechanisms.

• Journal of KIISE:Information Networking
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• v.30 no.4
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• pp.559-571
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• 2003

ENUM(tElephon NUmbering Mapping) is protocol that brings convergence between PSTN Networks and IP Networks using a unique worldwide E.164 telephone number as an identifier between different communication infrastructure. The mechanism provides a bridge between two completely different environments with E.164 number; IP based application services used in PSTN networks, and PSTN based application services used in IP networks. We propose a new way to organize and handle ENUM Tier 2 name servers to improve performance at the name resolution process in ENUM based application service. We build an ENUM based network model when NAPTR(Naming Authority PoinTeR) resource record is registered and managed by area code at the initial registration step. ENUM promises convenience and flexibility to both PSTN and IP users, yet there is no evidence how much patience is required when users decide to use ENUM instead of non-ENUM based applications. We have estimated ENUM response time, and proved how to improve performance up to 3 times when resources are managed by the proposed mechanism. The proposition of this thesis favorably influences users and helps to establish the policy for Tier 2 name server management.

• Journal of the Institute of Convergence Signal Processing
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• v.12 no.2
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• pp.133-138
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• 2011

In IP-based wireless sensor networks (WSNs), it might be necessary to distribute application updates to the sensor nodes in order to fix bugs or add new functionality. However, physical access to nodes is in many cases extremely limited following deployment. Therefore, network reprogramming protocols have recently emerged as a way to distribute application updates without requiring physical access to sensor nodes. In order to solve the network reprogramming problem over the air interface, this thesis presents a new scheme for new update code propagation using fragmentation scheme and network coding. The proposed code propagation method roughly shows reduced performance improvement in terms of the number of data exchange compared with the previously proposed pipelining scheme. Further, It is shows enhanced reliability for update code propagation and reduced overhead in terms of the number of data exchange. As a result, we can efficiently perform the software update from the viewpoint of speed, energy, and network congestion when the proposed code propagation system is applied. In addition, the proposed system solves overhearing problems of network coding such as the loss of original messages and decoding error using the predefined message. Therefore, our system allows a software update system to exchange reliable data in wireless sensor networks.

• KIPS Transactions on Computer and Communication Systems
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• v.7 no.3
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• pp.81-90
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• 2018

Due to the dramatic advancement of IoT (Internet of Things), it is expected that tens of billions of IoT devices will be connected by the year 2024. Furthermore, as IoT technologies evolves, the security management in IoT platforms has become a critical issue. For example, there are interworking problems between heterogeneous IoT platforms caused by differences from communication protocols, security policies, etc. in each platform. In addition, unsecured interworking can cause major security issues including the information leakage. In this paper, in order to solve these problems, a security interworking architecture is proposed and implemented in both FIWARE and oneM2M, which are representative IoT platforms. First, the security architecture of FIWARE is analyzed and implemented, and then the security framework based on OAuth 2.0 is developed on Mobius platform. Finally, in order to validate the proposed security interworking architecture, a LED (Light-Emitting Diode) example, where the LED is controlled by only authorized users, is developed. The proposed architecture can be extended to the diverse IoT platforms and devices.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.7
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• pp.613-621
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• 2016

This research connected network equipment, including CCTV, PAGA, IP-PBX, and Legacy, in order to enable the operation and configuration of internal IP-based network equipment in maritime plants and vessels, both in the field and from remote places, and to allow for the support of remotely controlling such equipment. It also realized an operating program for the integrated network equipment management system to enable the monitoring and control of equipment status, operation condition, and notifications from distant places. By applying the operating program to satellite stations and vessels sailing on the sea, a performance test was conducted to evaluate data loss and transmission/reception delay in the communication section between the land and vessels. As a result, this research verified the normal operation of CCTV control and of real-time monitoring and control of the network equipment, including PAGA, IP-PBX, and Legacy under the FBB and MVSAT environments. It was observed that the transmission of CCTV video images with a large volume of data as well as the transmission and reception of voice data were found to be slightly delayed, indicating the need to develop technology to compress and convert data for real-time transmission and reception.

• Proceedings of the Korea Inteligent Information System Society Conference
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• 2002.05a
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• pp.140-148
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• 2002

컴퓨터를 통해 편리한 생활을 추구해온 인간들은 전자상거래 분야에서도 이러한 욕구를 충족시키기 위해 자동협상이라는 기능을 요구하게 되었다. 지능형 에이전트를 이용한 자동협상은 인간의 거래협상 업무의 부담을 많은 부분을 덜어주고 있어 자동협상 에이전트에 관한 연구들이 활성화되고 있다 소비자간 전자상거래에서는 다수의 자동협상 에이전트 연구들이 경매시장에서의 자동협상에 초점을 맞추고 있는데 반해, 가격 이외의 여러 거래속성을 갖는 상품에 대한 제안기반 협상시장에서의 자동협상 에이전트에 관한 연구들이 최근에 활발히 이루어지고 있다. 본 연구에서는 소비자간 전자상거래에서 거래속성의 변화에 따라 개인의 효용가치의 차이를 이용한 다속성 상품의 제안기반 협상시장이 가져야할 특성에 대해 연구하고, 이를 기반으로 자동 거래협상을 수행에 필요한 거래속성 변화에 따른 소비자 개인의 선호체계를 표현하기 위한 방법을 개발하였다. 그리고 이러한 자동 거래협상을 공정하게 수행하기 위해 협상시장이 가져야할 특징과 프로토콜을 제안하고 시장운영 에이전트 시스템의 구조를 설계하였다. 마지막으로 이러한 분산형 시장구조를 갖는 제안기반의 협상시장에 참여하는 사용자 에이전트 시스템이 최적의 거래상대와 최적의 거래안을 찾기 위한 탐색방법을 구체적으로 개발하였다. 본 연구의 결과를 통하여 소비자간 전자상거래에서 구매자 뿐만 아니라 판매자도 협상결과에 따른 거래로 얻어지는 자신의 효용을 극대화할 수 있는 공정한 협상시장을 운영할 수 있을 뿐만 아니라 사용자들도 손쉽게 자신의 협상 선호체계를 쉽게 표현하고, 표현된 선호체계를 반영한 자동 거래협상을 수행할 수 있을 것 이다. 기존의 UN/EDIFACT표준을 사용하고 있는 EDI환경과 기존 VAN 방식의 EDI 중계 시스템과 연동되며, 향후 관세청의 XML/EDI 표준 시행을 미리 대비하는 선도연구로서 자리매김이 된다. 본 연구에서는 개발된 XML/EDI 통관시스템은 향후, 서비스의 최대 걸림돌이 되어왔던 값비싼 EDI 사용료의 부담에서 벗어날 수 있게 할 것이며, 저렴한 EDI구축/운영 비용으로 전자문서교환의 활성화와 XML이 인터넷 기반의 문서유통 표준으로 자리매김할 수 있는 중요한 계기가 될 것이다.재무/비재무적 지표를 고려한 인공신경망기법의 예측적중률이 높은 것으로 나타났다. 즉, 로지스틱회귀 분석의 재무적 지표모형은 훈련, 시험용이 84.45%, 85.10%인 반면, 재무/비재무적 지표모형은 84.45%, 85.08%로서 거의 동일한 예측적중률을 가졌으나 인공신경망기법 분석에서는 재무적 지표모형이 92.23%, 85.10%인 반면, 재무/비재무적 지표모형에서는 91.12%, 88.06%로서 향상된 예측적중률을 나타내었다.ting LMS according to increasing the step-size parameter $\mu$ in the experimentally computed. learning curve. Also we find that convergence speed of proposed algorithm is increased by (B+1) time proportional to B which B is the number of recycled data buffer without

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.1
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• pp.31-46
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• 2012

The most critical technology to implement ubiquitous health care is Ubiquitous Sensor Network (USN) technology which makes use of various sensor technologies, processor integration technology, and wireless network technology-Radio Frequency Identification (RFID) and Wireless Sensor Network (WSN)-to easily gather and monitor actual physical environment information from a remote site. With the feature, the USN technology can make the information technology of the existing virtual space expanded to actual environments. However, although the RFID and the WSN have technical similarities and mutual effects, they have been recognized to be studied separately, and sufficient studies have not been conducted on the technical integration of the RFID and the WSN. Therefore, EPCglobal which realized the issue proposed the EPC Sensor Network to efficiently integrate and interoperate the RFID and WSN technologies based on the international standard EPCglobal network. The proposed EPC Sensor Network technology uses the Complex Event Processing method in the middleware to integrate data occurring through the RFID and the WSN in a single environment and to interoperate the events based on the EPCglobal network. However, as the EPC Sensor Network technology continuously performs its operation even in the case that the minimum conditions are not to be met to find complex events in the middleware, its operation cost rises. Moreover, since the technology is based on the EPCglobal network, it can neither perform its operation only for the sake of sensor data, nor connect or interoperate with each information system in which the most important information in the ubiquitous computing environment is saved. Therefore, to address the problems of the existing system, we proposed the design and implementation of USN integration management system. For this, we first proposed an integration system that manages RFID and WSN data based on Session Initiation Protocol (SIP). Secondly, we defined the minimum conditions of the complex events to detect unnecessary complex events in the middleware, and proposed an algorithm that can extract complex events only when the minimum conditions are to be met. To evaluate the performance of the proposed methods we implemented SIP-based integration management system.