• Journal of Communications and Networks
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• 제3권4호
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• pp.334-341
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• 2001

The provision of QoS control is a key of the successful deployment of multimedia networks. Buffer management plays an important role in QoS control. Therefore, this paper proposes a novel QoS buffer management algorithm named GREEN (Global Random Early Estimation for Nipping), which extends the concepts of ERD (early random drop) and RED (random early detection). Specifically, GREEN enhances the concept of "Random" to "Global Random" by globally considering the random probability function. It also enhances the concept of "Early" to "Early Esti mation" by early estimating the network status. For performance evaluation, except compared with RED, extensive simulation cases are performed to probe the characteristics of GREEN.

• 한국정보통신학회논문지
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• 제11권10호
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• pp.1950-1956
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• 2007

IEEE 802.16e는 여러 가지 면에서 개선의 여지를 남기고 있으며 그중 특히 고속 핸드오버는 사용자가 고속으로 이동하는 환경에서는 필수적인 요소이다. 이 논문에서는 핸드오버 후보 기지국을 활용하는 고속 핸드오버 방식을 제안하였다. 제안된 방식은 IEEE 802.16e에 기반을 두고 있지 만 모의실험을 통한 성능 분석 결과에 의하면 핸드오버 지연을 기존 방식 대비 30%이상 감소시키며 핸드오버 탈락 확률 또한 5% 이상 향상시키는 성능개선 결과를 나타내었다.

• 한국통신학회논문지
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• 제29권7B호
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• pp.711-721
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• 2004

To provide the end-to-end service differentiation for assured services, the random early demotion and promotion (REDP) marker in the edge router at each domain boundary monitors the aggregate flow of the incoming in-profile packets and demotes in-profile packets or promotes the previously demoted in-profile packets at the aggregate flow level according to the negotiated interdomain service level agreement (SLA). The REDP marker achieves UDP fairness in demoting and promoting packets through random and early marking decisions on packets. But, TCP fairness of the REDP marker is not obvious as fur UDP sources. In this paper, to improve TCP fairness of the REDP marker, we combine a dropper with the REDP marker. To make packet transmission rates of TCP flows more fair, at the aggregate flow level the combined dropper drops incoming excessive in-profile packets randomly with a constant probability when the token level in the leaky bucket stays In demotion region without incoming demoted in-profile packets. It performs a dropping in the demotion at a domain boundary only if there is no prior demotion. The concatenate dropping at multiple domains is avoided to manifest the effect of a dropping at a domain boundary on TCP fairness. We experiment with the REDP marker with the combined dropper using ns2 simulator for TCP sources. The simulation results show that the REDP marker with the combined dropper improves TCP fairness in demoting and promoting packets by generating fair demoted in-profile traffic compared to the REDP marker. The effectiveness of the selected drop probability is also investigated with showing its impact on the performance of the REDP marker with the combined dropper.

• 한국추진공학회지
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• 제18권4호
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• pp.74-80
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• 2014

본 논문은 무유도 로켓탄의 명중률을 향상시키기 위해 개발한 이중추력형 비행모터에 관하여 기술하였다. 고연소속도 특성을 지닌 더블베이스 추진제의 형상 조절을 통해 이중추력형 비행모터를 설계하였으며, 실제 지상연소시험을 통해 이중추력 성능을 확인하였다. 연소시험 결과 서스테이닝 단계와 부스팅 단계의 추력비는 약 1:7.6으로 정상적인 이중추력 특성을 보였으며, 압력강하에 의한 추진제 소화현상은 나타나지 않았다.

• 한국건설순환자원학회논문집
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• 제6권3호
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• pp.153-159
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• 2018

지하구조물에 주로 발생하는 탄산화는 콘크리트 내부의 공극수의 pH감소에 따라 부식을 유발할 수 있으므로 많은 연구가 진행되고 있다. 그러나 이산화탄소로부터 표면을 보호하는 간단한 표면 보수방법을 통하여 구조물의 내구수명의 연장이 가능하다. 기존의 결정론적 유지관리 기법과는 다르게, 확률론적 유지관리 기법에서는 내구수명의 변동성이 고려될 수 있으나 정규분포만 다루고 있다. 본 연구에서는 정규분포 이외에 로그분포를 고려할 수 있는 수명-확률분포를 유도하였으며, 이를 기초로 다양한 수명-확률분포 함수를 고려한 보수비 산정기법을 제안하였다. 제안된 기법은 초기의 내구수명 분포 또는 보수재를 통하여 연장된 내구수명 분포가 정규 또는 로그분포를 가질 경우 목표내구수명의 연장에 따라 확률론적 기법을 통하여 보수비를 평가할 수 있다. 보수를 통한 내구수명이 로그분포를 가질 경우 효과적으로 보수비를 감소시킬 수 있으며, 장기 실험 또는 실태조사를 통하여 내구수명 분포가 정의될 수 있다면 더욱 합리적인 유지관리 계획을 수립할 수 있을 것으로 판단된다.

• 한국통신학회논문지
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• 제25권8A호
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• pp.1177-1185
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• 2000

본 논문에서는 긴 전파 지연과 높은 에러율을 지닌 위성링크에 TCP를 사용하는 경우 나타나는 문제점을 도출하고 그에 대한 성능향상방안으로 ENA(Error Notification Ack) 알고리즘을 제안했다. TCP는 에러에 의한 세그먼트 손실과 Network Congestion에 의한 손실을 구분하지 못하고 두 경우 모두 Network Congestion 으로 판단한 후 Slow Start나 Congestion Aboidance 알고리즘을 적용시킨다 위성링크에서는 에러에 의한 세그먼트 손실이 자주 발생하는데 이손실을 Network Congestion에 의한 손실로 받아들여 매번 Congestion Control 알고리즘을 적용시킨다 그로인해 전송률을 줄어들고 성능은 급격히 떨어진다. 본 논문에서는 에러에 의한 손실과 Congestion 의한 손실을 구분해 주는 ENA 알고리즘을 제안하고 구현 방법 또한 제시하였다 그리고 ENA 알고리즘을 Tahoe, Reno. Sack TCP에 적용하여 성능의 변화를 비교 분석했다 그 결과 에러율이 높을수록 성능이 더 향상됨을 알수 있었다.

• 한국정보처리학회논문지
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• 제6권11호
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• pp.3097-3107
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• 1999

Recently many studies have been done on the Random Early Detection(RED) algorithm as an active queue management and congestion avoidance scheme in the Internet. In this paper we first overview the characteristics of RED and the modified RED algorithms in order to understand the current status of these studies. Then we analyze the RED dynamics by investigating how RED parameters affect router queue behavior. We show the cases when RED fails since it cannot react to queue state changes aggressively due to the deterministic use of its parameters. Based on the RED parameter analysis, we propose a self-adaptive algorithm to cope with this RED weakness. In this algorithm we make two parameters be adjusted themselves depending on the queue states. One parameter is the maximum probability to drop or mark the packet at the congestion state. This parameter can be adjusted to react the long burst of traffic, consequently reducing the congestion disaster. The other parameter is the queue weight which is also adjusted aggressively in order for the average queue size to catch up with the current queue size when the queue moves from the congestion state to the stable state.

• Journal of information and communication convergence engineering
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• 제9권5호
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• pp.530-538
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• 2011

Performance of TCP can be severely degraded in Mobile IP-based wireless networks where packet losses not related to network congestion occur frequently during inter-subnetwork handoffs by user mobility. To solve such a problem in the networks using Mobile IP, the packet buffering method at a base station(BS) recovers those packets dropped during handoff by forwarding the buffered packets at the old BS to the mobile users. But, when the mobile user moves to a congested BS in a new foreign subnetwork, those buffered packets forwarded by the old BS are dropped and TCP transmission performance of a mobile user degrades severely. In this paper, we propose a Modified BLUE(MBLUE) buffer required at a BS to increase TCP throughput in Mobile IP-based networks. When a queue length exceed a threshold and congestion grows, MBLUE increases its packet drop probability. But, when a TCP connection is added at new BS by a handoff, the old BS marks the buffered packets. And new BS receives the marked packets without dropping. Simulation results show that MBLUE buffer reduces congestion during handoffs and increases TCP throughputs.

• Journal of Communications and Networks
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• 제8권1호
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• pp.93-105
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• 2006

The domination of the Internet by TCP-based services has spawned many efforts to provide high network utilization with low loss and delay in a simple and scalable manner. Active queue management (AQM) algorithms attempt to achieve these goals by regulating queues at bottleneck links to provide useful feedback to TCP sources. While many AQM algorithms have been proposed, most suffer from instability, require careful configuration of nonintuitive control parameters, or are not practical because of slow response to dynamic traffic changes. In this paper, we propose a new AQM algorithm, hybrid random early detection (HRED), that combines the more effective elements of recent algorithms with a random early detection (RED) core. HRED maps instantaneous queue length to a drop probability, automatically adjusting the slope and intercept of the mapping function to account for changes in traffic load and to keep queue length within the desired operating range. We demonstrate that straightforward selection of HRED parameters results in stable operation under steady load and rapid adaptation to changes in load. Simulation and implementation tests confirm this stability, and indicate that overall performances of HRED are substantially better than those of earlier AQM algorithms. Finally, HRED control parameters provide several intuitive approaches to trading between required memory, queue stability, and response time.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권7호
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• pp.3018-3040
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• 2018

The mobility model is one of the most important factors that impacts the evaluation of any transportation vehicular networking protocols via simulations. However, to obtain a realistic mobility model in the dynamic urban environment is a very challenging task. Several studies extract mobility models from large-scale real data sets (mostly taxi GPS data) in recent years, but they do not consider the statuses of taxi, which is an important factor affected taxi's mobility. In this paper, we discover three simple observations related to the taxi statuses via mining of real taxi trajectories: (1) the behavior of taxi will be influenced by the statuses, (2) the macroscopic movement is related with different geographic features in corresponding status, and (3) the taxi load/drop events are varied with time period. Based on these three observations, a novel taxi mobility model (T-START) is proposed with respect to taxi statuses, geographic region and time period. The simulation results illustrate that proposed mobility model has a good approximation with reality in trajectory samples and distribution of nodes in four typical time periods.