• Title/Summary/Keyword: Congested traffic

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The Effect of Rain on Traffic Flows in Urban Freeway Basic Segments (기상조건에 따른 도시고속도로 교통류변화 분석)

  • 최정순;손봉수;최재성
    • Journal of Korean Society of Transportation
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    • v.17 no.1
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    • pp.29-39
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    • 1999
  • An earlier study of the effect of rain found that the capacity of freeway systems was reduced, but did not address the effects of rain on the nature of traffic flows. Indeed, the substantial variation due to the intensity of adverse weather conditions is entirely rational so that its effects must be considered in freeway facility design. However, all of the data in Highway Capacity Manual(HCM) have come from ideal conditions. The primary objective of this study is to investigate the effect of rain on urban freeway traffic flows in Seoul. To do so, the relations between three key traffic variables(flow rates, speed, occupancy), their threshold values between congested and uncontested traffic flow regimes, and speed distribution were investigated. The traffic data from Olympic Expressway in Seoul were obtained from Imagine Detection System (Autoscope) with 30 seconds and 1 minute time periods. The slope of the regression line relating flow to occupancy in the uncongested regime decreases when it is raining. In essence, this result indicates that the average service flow rate (it may be interpreted as a capacity of freeway) is reduced as weather conditions deteriorate. The reduction is in the range between 10 and 20%, which agrees with the range proposed by 1994 US HCM. It is noteworthy that the service flow rates of inner lanes are relatively higher than those of other lanes. The average speed is also reduced in rainy day, but the flow-speed relationship and the threshold values of speed and occupancy (these are called critical speed and critical occupancy) are not very sensitive to the weather conditions.

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A Method of Authenticating WLAN APs for Smartphones (스마트폰을 위한 무선 AP 인증 방법)

  • Shin, DongOh;Kang, Jeonil;Nyang, DaeHun;Lee, Sokjoon;Lee, KyungHee
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.39B no.1
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    • pp.17-28
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    • 2014
  • The increase of smartphone users have made mobile carriers offload increasingly congested traffic of 3/4G by providing Wi-Fi hot-spots in the public places such as coffee shops and subway stations. In the traditional authentication in WLAN, the users should convince the service providers that they are valid customers before they use WLAN services. Since the authentication protocol is designed for service providers. Even with the mutual authentication based on the IEEE 802.1X, which is supported by IEEE 802.11 standard, it is difficult to be convinced of that the service providers really have installed the WLAN APs, which users are confronted with. An attacker can install rogue APs that masquerade as legitimate APs by copying the SSID, MAC address, etc. in order to obtain users' private information. In this paper, we introduce a method of authenticating legitimate APs for smartphone users. And we show our proposal can be well utilized for the current Wi-Fi hot-spots as a security plug-in and prove it through our experiments.

Comparison of Area Pricing and Cordon Pricing in General Equilibrium Models (구역혼잡통행료와 진입통행료의 비교)

  • Yu, Sang-Gyun;Jeong, Chang-Mu;Lee, Hyeok-Ju
    • Journal of Korean Society of Transportation
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    • v.27 no.2
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    • pp.145-155
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    • 2009
  • This paper compares the relative performances of area and cordon tolls as opposed to the first-best congestion tolls with respect to alleviation of traffic congestion and social welfare. The comparison is done in the monocentric city where all the jobs are located at the city center. The study shows that the size of charging zones is similar in the two second-bests, but that the optimal toll level is higher in area pricing than in cordon pricing. Area pricing schemes turn out to perform better than cordon pricing schemes as measured by average speeds and daily average travel time. Accordingly, the former is shown to increase the social welfare more than the latter. In the case of the cordon tolls, the residents at the charging zones are exempted from the tolls. In this way, cordon tolls invite people into the most congested areas over the optimal level while partially negating the whole spirit of the congestion tolls.

Tiered-MAC: An Energy-Efficient Hybrid MAC Protocol for Wireless Sensor Networks (Tiered-MAC: 무선 센서 네트워크를 위한 에너지 효율적인 하이브리드 MAC 프로토콜)

  • Lee, Han-Sun;Chung, Kwang-Sue
    • Journal of KIISE:Information Networking
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    • v.37 no.1
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    • pp.42-49
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    • 2010
  • Because sensor nodes operate with the limited power based on battery which cannot be easily replaced, energy efficiency is a fundamental issue pervading the design of communication protocols developed for wireless sensor networks. In wireless networks, energy efficient MAC protocols can usually be described as being either a contention-based protocol or a schedule-based protocol. It is suitable to use combination of both contention-based protocol and schedule-based protocol, because the strengths and weaknesses of these protocols are contrary to each other. In this paper, in order to minimize energy consumption of sensor nodes and maximize network lifetime, we propose a new MAC protocol called "Tiered-MAC" The Tiered-MAC uses a schedule-based TDMA inside maximum transmission range of sink node and a contention-based CSMA otherwise. Therefore, by efficiently managing the congested traffic area, the Tiered-MAC reduces the unnecessary energy consumption. Based on the ns-2 simulation result, we prove that the Tiered-MAC improves the energy-efficiency of sensor network nodes.

CASPER: Congestion Aware Selection of Path with Efficient Routing in Multimedia Networks

  • Obaidat, Mohammad S.;Dhurandher, Sanjay K.;Diwakar, Khushboo
    • Journal of Information Processing Systems
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    • v.7 no.2
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    • pp.241-260
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    • 2011
  • In earlier days, most of the data carried on communication networks was textual data requiring limited bandwidth. With the rise of multimedia and network technologies, the bandwidth requirements of data have increased considerably. If a network link at any time is not able to meet the minimum bandwidth requirement of data, data transmission at that path becomes difficult, which leads to network congestion. This causes delay in data transmission and might also lead to packet drops in the network. The retransmission of these lost packets would aggravate the situation and jam the network. In this paper, we aim at providing a solution to the problem of network congestion in mobile ad hoc networks [1, 2] by designing a protocol that performs routing intelligently and minimizes the delay in data transmission. Our Objective is to move the traffic away from the shortest path obtained by a suitable shortest path calculation algorithm to a less congested path so as to minimize the number of packet drops during data transmission and to avoid unnecessary delay. For this we have proposed a protocol named as Congestion Aware Selection Of Path With Efficient Routing (CASPER). Here, a router runs the shortest path algorithm after pruning those links that violate a given set of constraints. The proposed protocol has been compared with two link state protocols namely, OSPF [3, 4] and OLSR [5, 6, 7, 8].The results achieved show that our protocol performs better in terms of network throughput and transmission delay in case of bulky data transmission.

A Congestion release Advertisement Method to Improve the IEEE 802.17 Resilient Packet Ring (체증해제 통보에 방식에 의한 IEEE 802.17 레질런트 패킷 링의 성능개선 연구)

  • Kim Tae-joon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.30 no.9B
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    • pp.581-590
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    • 2005
  • The IEEE 802.17 Resilient Packet Ring Working Group develops standards to support the development and deployment of Resilient Packet Ring networks in Local, Metropolitan, and Wide Area Networks for resilient and efficient transfer of data Packets at rates scalable to many gigabits Per second. It was known that the fairness algorithm of the IEEE 802.17 Resilient Packet Ring suffers from throughput degradation under an unbalanced overload. This Paper proposes a congestion release advertisement method to improve this throughput degradation and discusses its performance. Under the proposed method, a congested node decides whether its congestion is released or not. If released, it advertises the congestion release to upstream nodes, and then upstream nodes transmit their traffic without uy regulation. The proposed method is compatible with the legacy fairness algorithm.

Emission Characteristics of a Passing Two-stroke Scooter using at a Roadside Measurement (도로변 측정을 이용한 2행정 스쿠터의 대기오염물질 배출특성 연구)

  • Woo, Dae-Kwang;Lee, Seung-Bok;Bae, Gwi-Nam;Lim, Cheol-Soo;Kim, Tae-Sung
    • Journal of Korean Society for Atmospheric Environment
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    • v.27 no.6
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    • pp.663-671
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    • 2011
  • Although a scooter is a convenient transportation means for a short distance traveling with a light package in the congested urban center, it might be one of the significant sources of air pollutants to which many people can easily be exposed during its passing-by. In this paper, we measured concentrations of gases and particles emitted from a scooter at roadside with no other traffic. To understand the characteristics of scooter emissions with respect to driving speed (idling, 30 km/h) at the roadside, total particle number concentration, particle size distribution, average surface area of particles deposited in the alveolar region, and concentrations of black carbon, CO, and $NO_x$ were measured. The concentrations of the particle number, surface area of deposited particles, CO, and $NO_x$ were highly fluctuated in the scooter's idling condition. The trends of particle number concentration, CO, and $NO_x$ generation were similar to one another. When the scooter started to move, all of $NO_x$, CO and particle number concentrations increased and after it passed by at the speed of 30 km/h, the concentration peaks of the particles and gases appeared at the same time. Unimodal size distribution with ~70 and ~93 nm mode diameters was observed for the idling and cruising condition, respectively. From this work, we found that emission from a passing vehicle could be characterized using a roadside monitoring technique.

TCP CAE : Improving Wireless TCP under Reverse Background Congestion through Comparative ACK-based Estimator (TCP CAE: ACK기반 역방향 네트워크의 혼잡 감지기법)

  • Kim, Jae-Hyun;Choo, Hyun-Seung
    • Journal of Internet Computing and Services
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    • v.9 no.4
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    • pp.21-27
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    • 2008
  • TCP receivers deliver ACK packets to senders for reliable end-to-end transfer. When ACK packets are not transferred properly because of network congestion, the performance of TCP degrades. This paper proposes a reverse congestion warning mechanism and a congestion handling mechanism in heterogeneous networks with heavy background traffic in the backward direction. Help from TCP receivers or hardware such as routers and gateways other than the ACK packets themselves is not necessary. TCP senders compare the arrival intervals of ACK data passed from receivers and the difference in t imestamp values echoed by receivers. According to the simulation results using the NS-2 network simulator, the proposed scheme shows a performance elevation of 20% greater than Reno, 150% greater than New Reno, and 450% greater than Westwood, respectively, under heterogeneous networks and that the error rate of the radio link is 1% when the backward network is congested.

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Physical Layer Diversity and its Effects on the Performance of WLANs (물리 계층의 다양성과 무선 랜의 성능에 미치는 영향)

  • Choi, Sunwoong;Park, Kihong;Kim, Chong-Kwon
    • Journal of KIISE:Information Networking
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    • v.32 no.6
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    • pp.723-731
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    • 2005
  • Wide spread deployment of infrastructure WLANs has made Wi Fi an integral part of today's Internet access technology. Despite its crucial role in affecting end to end performance, past research has focused on MAC protocol enhancement, analysis and simulation based performance evaluation without sufficient consideration for modeling inaccuracies stemming from inter layer dependencies, including physical layer diversity, that significantly impact performance. We take a fresh look at IEEE 802.11 WLANs, and using experiment, simulation, and analysis demonstrate its surprisingly agile performance traits. Contention based MAC throughput degrades gracefully under congested conditions, enabled by physical layer channel diversity that reduces the effective level of MAC contention. In contrast, fairness and jitter significantly degrade at a critical offered load. This duality obviates the need for link layer flow control for throughput improvement but necessitates traffic control for fairness and QoS. We use experimentation and simulation in a complementary fashion, pointing out performance characteristics where they agree and differ.

A Distributed Wireless Local Area Network (WLAN) Access Scheme for Efficient WLAN Communication in Busy Train Stations (혼잡 철도 역사에서 효율적인 무선랜 통신을 위한 무선랜 분산 접속 방법)

  • Koh, Seoung-Chon;Choi, Kyu-Hyoung;Kim, Ronny Yongho
    • Journal of the Korean Society for Railway
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    • v.17 no.6
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    • pp.402-409
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    • 2014
  • Wireless local area network (WLAN) is a widely used wireless access method due to its easy usability and excellent performance. However, its performance degrades significantly as the number of users increases. In busy train stations, where the number of WLAN users are large and, more importantly the number of simultaneous packet transmission attempts is extremely large due to the time synchronization upon train arrival, the packet transmission delay problem is very severe and almost impossible for WLAN stations to initiate communication with WLAN networks. In this paper, a novel distributed WLAN access scheme for efficient WLAN communication in busy train stations is proposed. Using the proposed scheme, WLAN access delay can be significantly reduced under highly congested traffic environments. Therefore, a significant performance enhancement for the WLAN performance used in the Communication Based Train Control (CBTC) can be achieved.