• Information and Communications Magazine
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• v.24 no.3
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• pp.87-96
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• 2007

HSPA는 HSDPA 및 HSUPA를 통합하여 일컫는 3GPP 기술로 하향 링크에서는 HSDPA를 상향 링크에서는 HSUPA를 사용하여 기존 DCH만을 사용하는 3GPP Release 99 시스템 대비 더 효율적인 고속 멀티미디어 서비스를 제공하는 기술이다. HSDPA는 3GPP Release 5 기술로서 2002년 3월 첫 표준이 승인되었으며 단말의 무선 환경에 따라 변조 및 코딩기법을 변화시키는 AMC, 물리 계층을 통해 빠른 재전송을 지원하는 HARQ,단축된 2ms TTI 그리고 Node-B 기반의 고속 스케줄링을 통해 무선망 성능을 획기적으로 향상시켜 하향 링크에서 최대 14.4Mbps를 제공한다. HSUPA는 3GPP Release 6 기술로서 2004년 6월 첫 표준이 승인되었으며 HSDPA에 도입한 기술들 중에서 AMC를 제외한 모든 기술을 적용하여 상향 링크에서 최대 5.76Mbps를 제공한다. HSPA Evolution(eHSPA 또는 HSPA+)은 HSPA의 성능 개선을 통해 3GPP Release 8 기술인 LTE로의 자연스러운 진화를 보장하기 위한 3GPP Release 7 기술로 2006년 3월 TSG RAN #31 회의에서 승인되었다. 본 고에서는 최근 표준화가 활발히 진행되고 있는 HSPA Evolution에서 최근까지 승인된 각 계층별 요소 기술에 대해 소개하고자 한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2000.04a
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• pp.698-703
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• 2000

초고속 인터넷의 멀티미디어 서비스 통합에 대한 해결책으로 ATM 네트워크 기술이 널리 사용되고 있다. UBR 상의 TCP에서는 혼잡 시 패킷의 손실을 줄이기 위한 UBR+EPD 방식과 ABR 상의 TCP에서 ABR 율 기반 제어는 셀 손실을 억제하는 높은 성능의 ER 방식이 제안되었다. 그러나 인터넷 서비스의 영역이 지역적으로 점차 확장되어짐에 따라 보다 다양한 QoS가 요구되어진다. 이러한 환경요인을 만족시키기 위해, 본 논문에서는 UBR 서비스상의 TCP의 성능개선을 위해서 거리에 따른 빠른 재전송과 회복의 설정 여부에 대한 성능평가와 ABR 서비스에서는 TCP의 파라미터인 MTU(Maximum Transport Unit)의 크기를 변화시켜 좋은 성능 개선을 가져오는 MTU 크기를 시뮬레이션 결과 통해 나타내었다.

• Proceedings of the Korea Information Processing Society Conference
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• 2011.11a
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• pp.979-981
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• 2011

전체 모바일 시장에서의 스마트폰의 시장점유율이 빠른 속도로 증가하고 있는 가운데 스마트폰 보안 이슈에 대한 관심도 같이 증가되고 있으며, 스마트폰의 분실 및 도난으로 인한 피해의 대응책이 필요하다. 스마트폰의 특성상 휴대성 때문에 분실 및 도난시에 개인정보 유출 등의 2차적 피해가 커질 수 있다. 이러한 피해들을 최소화하기 위해 원격 동기화, 개인정보 접근 차단, 위치정보 송/수신, 원격 카메라 제어, 이벤트 로그 전송 등의 기능을 통해 스마트폰 내부에 저장되는 사용자의 개인정보의 유출을 방지하고 분실 및 도난된 스마트폰의 재습득 가능성을 증대시킬 수 있다. 본 논문에서는 이러한 스마트폰의 분실 및 도난에 대비하는 보안 원격제어 관리 시스템을 제안, 설계하고 구현한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.11a
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• pp.1202-1205
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• 2007

최근 무선랜의 이용이 급격하게 증가하고 있는 추세이다. 무선랜은 이동통신에 비해 빠른 데이터 전송이 가능하여 화상통신, VoIP, 동영상 스트리밍 등 멀티미디어 서비스에 적합하다. 하지만 무선랜은 서비스 제공 영역이 작기 때문에 사용자가 자주 이동할 경우 핸드오프가 발생하여 딜레이가 증가한다. 딜레이에 민감한 멀티미디어의 경우 서비스 품질에 영향을 받을 수 있으므로 이에 대한 고려가 필요하다. 본 논문에서는 핸드오프의 인증 과정에서 발생하는 딜레이를 줄이기 위해 핸드오프 할 때 사용되는 임시 키인 THK 의 사용을 제안한다. THK 를 이용할 경우 인증 서버를 이용하지 않고도 인증이 가능하며 사용하는 메시지의 양도 작기 때문에 딜레이 감소가 가능하다. 시뮬레이션 결과는 우리가 제안한 프로토콜을 이용할 경우 현재 사용 중인 프로토콜에 비해 최고 2 배의 성능 향상을 얻을 수 있음을 보여준다.

• Journal of Korea Spatial Information System Society
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• v.1 no.2 s.2
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• pp.137-149
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• 1999

Spatial database systems in client-server environment have network overload due to the large amount of spatial data transmission. Users use the window query that loads partial region of a whole map for quick response time in the environment. A series of window query such as screen movement, enlargement or shrinkage requires data in similar region and this increases network overload by re-transmitting the same data in intersected region with the earlier transmitted region. Removing the transmitted data from query results can solve this problem. In this paper, we design and implement a spatial object manager in order to remove the intersected region occurred by a series of window query. The spatial object manager manages the object identifiers of transmitted objects and removes transmitted objects from spatial objects of the query result by using the removal technique of the intersected region for the transmission and comparison. We utilize GEOMania Millennium server, an open client-server spatial database system, as spatial object manager in this paper. The result of the performance evaluation shows that the spatial object manager removes the transmission of the data redundancy, reduces network overload and improves the overall system performance.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2021.10a
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• pp.469-471
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• 2021

As wireless communication technology advances to ensure high accuracy and safety at high speeds, research and development of Visible Light Communication (VLC) technology has been accelerated as an alternative to traditional radio frequency (RF) technology. As the radio spectrum of RF communication becomes more congested and demand for bandwidth continues to increase, VLCs that can use unlicensed frequency band are proposed as a solution. However, VLC channels have broadcasting characteristics that make them easily exposed to eavesdropping and jamming attacks, and are vulnerable to MITM (Man-In-The-Middle) due to their line of sight (LOS) propagation characteristics. These attacks on VLC channels compromise the confidentiality, integrity, and availability of communications links and data, resulting in higher data retransmission rates, reducing throughput and increasing power consumption, resulting in lower data transmission efficiency. In this work, we model vulnerable VLC channels to analyze the impact of attacks and communications vulnerabilities by malicious jammers.

• Journal of KIISE:Information Networking
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• v.34 no.6
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• pp.466-474
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• 2007

Asymmetric networks that the downlink bandwidth is larger than the uplink bandwidth may cause the degradation of the TCP performance due to the uplink congestion. In order to solve this problem, this paper designs and implements the Dynamic Segment Size Control mechanism which offers a suitable segment size for current networks. The proposed mechanism does not require any changes in customer premises but suppress the number of ACKs using segment reassembly technique to avoid the uplink congestion. The gateway which adapted the Dynamic Segment Size Control mechanism, detects the uplink congestion condition and dynamically measures the bandwidth asymmetric ratio and the packet loss ratio. The gateway reassembles some of segments received from the server into a large segment and transmits it to the client. This reduces the number of corresponding ACKs. In this mechanism, the SACK option is used when occurs the bit error during the transmission. Based on the simulation in the GEO satellite network environment, we analyzed the performance of the Dynamic Segment Size Control mechanism.

• Journal of Korea Multimedia Society
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• v.15 no.8
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• pp.1038-1047
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• 2012

The SIP(Session Initation Protocol) is an application layer protocol that is used to establish, release, and change the call session of the IP telephony. In the SIP signalling networks, when the number of the UA(User Agent) requested the call session increase, the number of messages to be processed by SIP proxy server increase. It often will be caused the overload of the SIP proxy server. In this paper, we proposed the overload control method with a normal queue and a delay queue in the SIP proxy server. When it is estimated the overload of the server by the excess of the high threshold in the normal queue, new INVITE messages will be put into the delay queue to reduce the load of the server. It results in some delay of the call session from the INVITE message. Subsequently when the number of messages in the normal queue is reduced below the low threshold, the INVITE messages in the delay queue is processed. The simulation results showed that the number of the retransmission messages by our proposed method was 45% less than the one by the method with single queue. The results also showed that the average call success rate by the proposed method was 2% higher than the one by the method with single queue.

• The KIPS Transactions:PartC
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• v.11C no.3
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• pp.379-386
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• 2004

The WAP 2.0 system is a newly proposed wireless communication system by the WAP Forum for interoperability across Internet environment and the system takes charge of communication between WAP terminals and existing origin Web servers. The purpose of this paper is 1) to construct a WAP 2.0 proxy proposed by the WAP Forum and 2) to improve the WAP Proxy in order to increase communication efficiency between wired and wireless communication objects. The Improved WAP proxy constructed in this study provides links between wired and wireless communication environments using the split-TCP concept. However, unlike the split-TCP connection, The improved WAP proxy maintains TCP's end-to-end semantics and reduces overhead by avoiding operations as much as possible on the upper protocol layer. In addition, The improved WAP proxy supports SACK(Selective Acknowledgement ) option and Timestamp option for speedy re-transmission which leads to reduction of performance degradation. After constructing the improved WAP proxy under Linux environment, experiments have been taken. The experimental results show that, compared with the experiments when a WAP proxy proposed by the WAP Forum is used, both data transmission delay time and data transmission size decrease to show that communication efficiency is increased. In particular, as packet missing ratio Increases, data transmission size decreases, which demonstrates that the improved WAP proxy is very effective for performance improvement in wireless communication environment.

• Journal of Korea Society of Industrial Information Systems
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• v.14 no.5
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• pp.11-18
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• 2009

Ajax based on Java Script receives attention as an alternative to ActiveX technology. Most portal sites in korea show a tendency to reopen existing services by combining the technology, because it supports most web browsers, and has the advantages of such a brilliant interface, excellent speed, and traffic reduction through asynchronous interaction. This paper modeled and implemented a multilingual meta-search service using the Ajax and open APIs provided by international famous sites. First, a Korean query is translated into one of the language of 54 countries around the world by Google translation API, and then the translated result is used to search the information of the social web sites such as Flickr, Youtube, Daum, and Naver. Searched results are displayed fast by dynamic loading of portion of the screen using Ajax. Our system can reduce server traffic and per-packet communications charges by preventing redundant transmission of unnecessary information.