• Proceedings of the Korea Information Processing Society Conference
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• 2009.11a
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• pp.503-504
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• 2009

최근 차세대 휴대 인터넷 기술로 주목받고 있는 WiMAX 네트워크의 성능을 향상시키기 위한 연구가 많이 진행되고 있다. WiMAX 네트워크을 이용하는 대부분의 응용들이 TCP/IP 계층을 사용하며 기존 TCP 전송기법들이 유선망을 주로 고려한 한계가 있으므로, WiMAX 네트워크 상에서의 전송 계층 성능 향상에 대한 연구의 필요성이 증대되고 있다. 본 논문에서는 실제 WiMAX 네트워크 상에서 기존 유선 네트워크에서 사용되던 TCP Reno, Veno, Westwood, Cubic 등의 TCP 혼잡제어 알고리즘들의 성능을 측정하고 비교, 분석하여 WiMAX 네트워크에서 TCP의 동작 특성을 살펴본다.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.2
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• pp.103-110
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• 2012

The population growth along with the urbanization, has caused more problems in many public areas, such as subway airport terminals, hospital, etc. Many surveillance systems have been installed in the public areas, but not all of those can be monitored in real-time, because the operators that observe the monitors are very small compared with the number of the monitors. For example, the observer can miss some crucial accidents or detect after considerable delays. Thus, intelligent surveillance system for preventing the accidents are needed, such as Intelligent Surveillance Systems. in this paper, we propose a new crowd density estimation method which aims at estimating moving crowd using images from surveillance cameras situated in outdoor locations. The moving crowd is estimated from the area where using optical flow. The edge information is also used as feature to measure the crowd density, so we improve the accuracy of estimation of crowd density. A multilayer neural network is designed to classify crowd density into 5 classes. Finally the proposed method is experimented with PETS 2009 images.

• Journal of Korean Society of Transportation
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• v.23 no.5 s.83
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• pp.7-14
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• 2005

Traffic congestion causes enormous social costs as well as loss of travel time and waste of energy. Though the Seoul metropolitan government implemented various forms of transportation policies such as urban road pricing and public transportation reform, traffic volume which across the Seoul metropolitan borders have greatly increased because of housing land development in suburban area. The purpose of this study is to estimate individual's willingness-to-pay(WTP) for extensive implementation of congestion pricing through policy-mix with bus rapid transit(BRT) system. So the field survey interviews carried out. The empirical analysis was done with priority given to the following two topics; derivation of individual WTP and prior evaluation of policy effect from the equity aspect. To estimate individual WTP, we adopted contingent valuation method (CVM). The former is to estimate individual WTP for respondent's maintaining his/her transit pattern when he/she is faced with congestion pricing by using compensating variation(CV) concept. And, the latter aims at evaluating policy effect from the equity aspect by calculating the Proportion of WTP to average income using WTP in income bracket for policy scenarios.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.11a
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• pp.513-514
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• 2009

최근 네트워크 성능이 고도화됨에 따라 종단간 네트워크 가용대역폭을 측정에 관한 연구가 활발하다. 종단간 네트워크 가용대역폭을 측정함으로써 네트워크 접근제어, 서비스 받을 서버 선택 문제, 오버레이 네트워크에서의 최적의 경로 선택, 혼잡제어 등에서 다양하게 응용할 수 있다. 본 논문에서는 기존 종단간 네트워크 가용대역폭을 측정하는 기법의 장단점에 대해 알아보고 가용대역폭 측정 툴들을 비교 분석해 보았다.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10c
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• pp.499-501
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• 2003

무선링크에서 TCP의 성능을 향상시키기 위한 연구들이 많이 수행되었으며, 다양한 기법들이 제안되고 있다. 하지만, 대부분의 연구들이 TCP 송신측이 무선링크에서의 패킷 손실을 혼잡으로 오해하는 문제를 해결하는데 초점을 맞추고 있다. 또한 이러한 연구들은 대부분 시뮬레이션을 통해 측정되고 검증된 결과들이기 때문에 실제 환경을 반영하는 데는 완전하지 않다. 본 논문에서는 SKT의 CDMA2000­1x 상용 망에서 삼성전자의 SPH­A500 단말기를 이용하여 TCP와 UDP의 성능을 측정하였다. 본 연구에서는 CDMA2000­1x의 정확한 특성을 측정하고 분석하여. 무선링크에서의 delay spike에 의한 불필요한 timeout을 방지하고, 병목 링크에서의 큐 길이를 안정되게 유지하는 방법을 고안하고자 한다. 이를 위해 본 논문에서는 측정 과정에서 분석된 CDMA2000­1x의 특성을 정리한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2023.11a
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• pp.832-833
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• 2023

최근 2022년 이태원 압사 사고, 2019년 김포 골드라인 개통 이후, 호전되지 않는 밀집도 및 혼잡률에 따른 안전사고 문제가 대두되고 있다. 밀집도 측정이 가능한 CCTV는 이미 존재하지만, 가격이 높고, 시스템 수정 및 적용에 제약이 존재하여 모든 장소에 적용할 수 없다는 한계점을 지니고 있다. 본 논문에서는 현재 상용화된 밀집도 측정 CCTV 시스템과는 다르게 기존 CCTV 시스템과의 상호 호환성을 기반으로 부가적인 비용이 크게 발생하지 않아 경제성이 존재하며, CCTV가 설치되어 있는 모든 장소에 적용이 가능한 확장성을 지닌 CCTV 기반 인원 밀집도 측정 시스템을 소개한다.

• 대한공업교육학회지
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• v.32 no.2
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• pp.199-216
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• 2007

Stream Control Transmission Protocol(SCTP) is a transport layer protocol to support the data transmission. SCTP is similar to Transmission Control Protocol(TCP) in a variety of aspects. However, several features of SCTP including multi-homing and multi-streaming incur the performance difference from TCP. This paper highlights the data transfer during the initial slow start phase in SCTP congestion control composed of slow start phase and congestion avoidance phase. In order to compare the mean transfer time between SCTP and TCP, we experiment with different performance parameters including bandwidth, round trip time, and data length. By varying data length, we also measure the corresponding initial window size, which is one of factors affecting the mean transfer time. For the experiment, we have written server and client applications by C language using SCTP socket API and have measured the transfer time by ethereal program. We transferred data between client and server using round-robin method. Analysis of these experimental results from the testbed implementation shows that larger initial window size of SCTP than that of TCP brings the reduction in the mean transfer time of SCTP compared with TCP by 15 % on average during the initial slow start phase.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.204-212
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• 2010

Currents which are generated at both ends of drive motor by operating brake pedal when subway train is driving, will generate the reviltalization actual effect if they are not used immediately. So there exist rolling stock established Dynamic braking annex for the purpose of stable brake performance in case there are no retrogress train around or no stable wiring voltage.Therefore 55% of entered energy are consumed in subway train. 45% are used in down gradient section or for regeneration energy and among them 25% are used for another train's retrogression through the wiring. So to reduce reviltalization method keeping the existing system, substation's service voltage should be declined about 5%. And then it will ease off excessive wiring voltage rise. And there need energy reduction by flexible service voltage adjustment and study for energy consumption efficiency in the subway.

• 전자공학회논문지 IE
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• v.43 no.3
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• pp.41-48
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• 2006

In this paper, we propose a new active queue management (AQM) scheme by utilizing the predictability of the Internet traffic. The proposed scheme predicts future traffic input rate by using the auto-regressive (AR) time series model and determines the future congestion level by comparing the predicted input rate with the service rate. If the congestion is expected, the packet drop probability is dynamically adjusted to avoid the anticipated congestion level. Unlike the previous AQM schemes which use the queue length variation as the congestion measure, the proposed scheme uses the variation of the traffic input rate as the congestion measure. By predicting the network congestion level, the proposed scheme can adapt more rapidly to the changing network condition and stabilize the average queue length and its variation even if the traffic input level varies widely. Through ns-2 simulation study in varying network environments, we compare the performance among RED, Adaptive RED (ARED), REM, Predicted AQM (PAQM) and the proposed scheme in terms of average queue length and packet drop rate, and show that the proposed scheme is more adaptive to the varying network conditions and has shorter response time.

• The KIPS Transactions:PartC
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• v.11C no.2
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• pp.235-244
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• 2004

TCP Vegas version provides better performance and more stable services than TCP Tahoe and Reno versions, which are widely used in the current Internet. However, in the situation where TCP Vegas and Reno share the bottleneck link, the performance of TCP Vegas is much smaller than that of TCP Reno. This unfairness is due to the difference of congestion control mechanisms of each TCP use. Several studies have been executed in order to solve this unfairness problem. In this paper, we analyze the minimum window size to maintain the maximum TCP performance of link bandwidth. In addition, we propose an algorithm which maintains the TCP performance and improves fairness by selective packet drops in order to allocate proper window size of each TCP connections. To evaluate the performance of the proposed algorithm, we have measured the number of data bytes transmitted between end-to-end systems by each TCP connections. The simulation results show that the proposed algorithm maintains the maximum TCP performance and improves the fairness.