• Journal of Korean Society for Atmospheric Environment
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• v.23 no.4
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• pp.498-506
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• 2007

To reduce the vehicular emissions of air pollutants, various traffic control programs (TCPs) have been used. In 2002, two TCPs have been implemented in Seoul and Busan, respectively. In this study, based on the study results on the effectiveness of the TCP in Seoul (Kim et al., 2005) and Busan (Lee et al., 2006), emission reduction by the TCP in Seoul was estimated and their contribution to the ambient air pollutants' concentrations was discussed. During the TCP period in 2002 at Seoul, emissions of air pollutants were reduced by 35% for CO and $NO_2$, 80% for HC, 23% for $PM_{10}$, and 24% for $SO_2$. Vehicular emission reduction affected the ambient concentrations significantly for $NO_2$. However, for $SO_2$, vehicular emission reduction did not affect the ambient concentration significantly. For $PM_{10}$, vehicular emission reduction did not affect the ambient concentration significantly if considering fugitive emissions.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.11
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• pp.2423-2428
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• 2010

The number of motor vehicle registrations in Korea is increasing steadily each year, driven by industry development and economic growth. The number of traffic accidents is also rapidly increasing. Korea has a relatively high number of traffic accidents among OECD member countries, and it ranks among the highest in traffic accident death rates. This death rate is higher compared to death rates as a proportion of the number of traffic accidents in each country. It is very common for drivers to lose consciousness in traffic collisions, which leads to a failure to carry out early emergency measures. In order to prevent such situations as well as hit-and-runs and people left uncared for after traffic accidents, there is a need for motor vehicle black boxes and accident report systems. This study addressed the need for an emergency evacuation system for people injured in traffic accidents and a secondary traffic accident prevention system by developing a motor vehicle emergency situation detection and report system combined with a black box, and materializing it as an actual system.

• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.887-890
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• 2001

레이어 코딩된 비디오의 경우 Base 스트림과 Enhancement 스트림으로 나누어지게 되는데 중요한 정보인 Base 스트림을 보장하고 Enhancement 스트림의 손실을 최소화 하는 방법의 연구가 많이 진행되어 왔다. 인터넷 망은 이러한 비디오 정보를 전송할 때 패킷의 크기와 전송간격, 그리고 프로토콜에 다양하게 영향을 받는다. 본 논문에서는 트래픽의 상당량을 차지하는 비디오를 레이어 코딩을 사용할 경우 생기는 트래픽 특성과 클라이언트의 네트워크변화에 따른 상황을 분석하고 패킷의 전송 방법을 프로토콜별로 효율성을 분석하며 Base 스트림의 Guaranteed 서비스를 보장하기 위해 TCP 스트리밍 방법을 제안한다.

• Proceedings of the KIEE Conference
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• 2000.11d
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• pp.815-817
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• 2000

근래 Web Server의 안정된 운용의 중요성이 급증하는 Network Traffic과 더불어 점차 증대되고 있다. 기본적인 Network 구성망은 Ethernet으로 표준적인 프로토콜은 TCP/IP로 기반을 잡고 있다. 날로 증가하는 Network Traffic을 효과적으로 처리하기 위해서는 Network의 bandwidth 및 서버가 처리할 수 있는 데이터 양을 분석하여 병목현상을 줄이고 데이터의 흐름을 원활히 하기 위한 데이터 buffer들의 설치와 적절한 운영 방법에 관한 연구가 필요하다. 본 논문에서는 Web Server로부터 image 데이터를 전송 받아 이를 원활히 display하기 위한 Application Layer에서의 buffer 크기 및 제어방법에 관한 연구를 수행하고 특히 연속적인 이미지의 전송과 재생에 관한 buffer management에 관하여 고찰한다.

• Annual Conference of KIPS
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• 2004.05a
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• pp.1007-1010
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• 2004

본 논문에서는 분산 서비스거부 공격(DDoS)이 발생할 때 네트워크 트래픽의 특성을 분석하기 위해서 트래픽 비율분석법(TRA: Traffic Rate Analysis)을 제안하고 트래픽 비율분석법을 통해서 분석된 다양한 유형의 DDoS 공격의 특성을 기계학습(Machine Learning)을 이용해서 DDoS 공격의 탐지규칙을 생성하고 그 성능을 측정하였다. 트래픽 비율분석법은 감시대상 네트워크 트래픽에서 특정한 유형의 트래픽의 발생비율을 나타내며 TCP flag rate 와 Protocol rate 로 구분된다. 트래픽 비율분석법을 적용한 결과 각각의 DDoS 공격 유형에 따라서 매우 독특한 특성을 가짐을 발견하였다. 그리고, 분석된 데이터를 대상으로 세 개의 기계학습 방법(C4.5, CN2, Na?ve Bayesian Classifier)을 이용해서 DDoS 공격의 탐지규칙을 생성하여 DDoS 공격의 탐지에 적용했다. 실험결과, 본 논문에서 제안된 트래픽 비율분석법과 기계학습을 통한 DDoS 공격의 탐지방법은 매우 높은 수준의 성능을 나타냈다.

• Annual Conference of KIPS
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• 2009.04a
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• pp.1112-1115
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• 2009

네트워크 관리자 입장에서 효율적인 네트워크 관리를 위해 응용 프로그램 별 트래픽 분류의 중요성이 커지고 있다. 응용 프로그램 별 트래픽 분류를 위해 signature 기반, machine learning 방법들이 제안되고 있지만 p2p 방식의 Skype 응용프로그램에 대한 적용결과는 그 신뢰성이 떨어지고 있는 것은 사실이다. 본 논문에서는 Skype의 트래픽을 분류하기 위해 각 Client 마다 Skype application install 시 동적으로 변화하는 Port 를 알아내는 방법, UDP 패킷의 특정위치의 특정 signature, TCP signal flow의 특정위치 패킷에 대한 payload 크기 등을 이용한 Skype traffic 분류 방법을 제안한다. 제안된 방법론은 학내 네트워크에 적용하여 그 타당성을 TMA를 통해 검증하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.6
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• pp.1881-1900
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• 2014

Since 802.11 wireless LANs are so widely used, it has become common for numerous access points (APs) to overlap in a region, where most of those APs are managed individually without any coordinated control. This pattern of wireless LAN usage is called the private OBSS (Overlapping Basic Service Set) environment in this paper. Due to frame collisions across BSSs, each BSS in the private OBSS environment suffers severe performance degradation. This study approaches the problem from the perspective of congestion control rather than noise or collision resolution. The retry limit, one of the 802.11 attributes, could be used for traffic control in conjunction with TCP. Reducing the retry limit causes early discard of a frame, and it has a similar effect of random early drops at a router, well known in the research area of congestion control. It makes the shared link less crowded with frames, and then the benefit of fewer collisions surpasses the penalty of less strict error recovery. As a result, the network-wide performance improves and so does the performance of each BSS eventually. Reducing the retry limit also has positive effects of merging TCP ACKs and reducing HOL-like blocking time at the AP. Extensive experiments have validated the idea that in the OBSS environment, reducing the retry limit provides better performance, which is contrary to the common wisdom. Since our strategy is basically to sacrifice error recovery for congestion control, it could yield side-effects in an environment where the cost of error recovery is high. Therefore, to be useful in general network and traffic environments, adaptability is required. To prove the feasibility of the adaptive scheme, a simple method to dynamically adjust the value of the retry limit has been proposed. Experiments have shown that this approach could provide comparable performance in unfriendly environments.

• Journal of KIISE:Information Networking
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• v.30 no.3
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• pp.437-447
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• 2003

In order to reduce the increasing packet loss rates caused by an exponential increase in network traffic, the IETF(Internet Engineering Task Force) is considering the deployment of active queue management techniques such as RED(Random Early Detection) algorithm. However, RED algorithm simple but does not protect traffic from high-bandwidth flows, which include not only flows that fail to use end-to-end congestion control such as UDP flow, but also short round-trip time TCP flows. In this paper, in order to solve this problem, we propose a simple fairness queue management scheme, called AFQM(Approximate Fair Queue Management) algorithm, that discriminate against the flows which submit more packets/sec than is allowed by their fair share. By doing this, the scheme aims to approximate the fair queueing policy Since it is a small overhead and easy to implement, AFQM algorithm controls unresponsive or misbehaving flows with a minimum overhead.

• Proceedings of the KIEE Conference
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• 2002.07d
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• pp.2631-2633
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• 2002

The rapid increase of traffic (amount) in metropolitan (big) cities makes the quality of urban life horrible/decreasing and costs much. Much efforts have been done to develop a good public transportation information system. However, it is not goof enough, its unsystematic and inefficient system forces citizens to use their own cars instead of using public transportation. Today high speed network is available everywhere and developing applications based on the internet is very popular. To solve the traffic congestion related problems, this paper tries to build, using TCP/IP and RS-232 protocol a system which can monitor the transportation situation in the matter of real-time on the internet.

• The KIPS Transactions:PartC
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• v.9C no.4
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• pp.605-614
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• 2002

Amount of the web traffic web server handles are explosively increasing, which requires that the performance of the web server should be improved for the various web services. Although the analysis for the HTTP traffic with the proper tuning for the web server is essential, the research relevant to the subject are insignificant. In particular, although most of applications are implemented over HTTP 1.1 protocol, the researches mostly deal with the performance evaluation of the HTTP 1.0 protocol. Consequently, the modeling approach and the performance evaluation over HTTP 1.1 protocol have not been well formed. Therefore, basing on the HTTP 1.1 protocol supporting persistent connection, we present an analytical end-to-end tandem queueing model for web server to consider the specific hardware configuration inside web server beginning at accepting the user request until completing the service. we compare various performances between HTTP 1.0 and HTTP 1.1 under the overloading condition, and then analyze the characteristics of the HTTP traffic that include file size requested to web server, the OFF time between file transfers, the frequency of requests, and the temporal locality of requests. Presented model is verified through the comparing the server throughput according to varying requests rate with the real web server. Thereafter, we analyze the performance evaluation of the web server, according to the interrelation between TCP Listen queue size, the number of HTTP threads and the size of the network buffers.