• 조명전기설비학회논문지
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• 제21권6호
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• pp.109-116
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• 2007

이동 애드 혹 네트워크(mobile ad hoc network)에서 적용되는 대부분의 라우팅 기술은 트래픽 부하를 고려하지 않아 네트워크 혼잡을 야기한다. 또한 이로 인해 트래픽 전송 성능을 저하시키고 네트워크 구성 노드들의 생존시간을 감소시킨다. 이를 해결하기 위해 본 논문에서는 모바일 애드 혹 네트워크에서 각 노드의 트래픽 상황을 고려한 리액티브(reactive) 경로 설정 기법을 제안한다. 제안하는 방안은 라우팅 경로 탐색 과정에서 노드의 트래픽 상황을 추정하여 과도한 트래픽이 집중될 경우 해당 노드를 중간 노드로 하는 라우팅 경로 생성을 억제한다. 특히 각 노드 단위로 신규 경로 설정 절차를 수행하기 때문에, 네트워크 전반에 걸친 트래픽 상황을 수집할 필요가 없다. 모의시험을 통해 제안하는 방안이 네트워크 전반에 트래픽을 잘 분산시키고 성능을 향상시키는 것을 보인다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권8호
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• pp.2875-2893
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• 2015

Existing coding aware routing algorithms focused on novel routing metric design that captures the characteristics of network coding. However, in packet coding algorithm, they use opportunistic coding scheme which didn't consider the queue state of the coding node and are equivalent to the conventional store-and-forward method in light traffic load condition because they never delay packets and there are no packets in the output queue of coding node, which results in no coding opportunity. In addition, most of the existing algorithms assume that all flows participating in the network have equal rate. This is unrealistic since multi-rate environments are often appeared. To overcome above problem and expand network coding to light traffic load scenarios, we present an enhanced coding-aware routing algorithm based on queue state and local topology (OQMCAR), which consider the queue state of coding node in packet coding algorithm where the control policy is of threshold-type. OQMCAR is a unified framework to merge single rate case and multiple rate case, including the light traffic load scenarios. Simulations results show that our scheme can achieve higher throughput and lower end-to-end delay than the current mechanisms using COPE-type opportunistic coding policy in different cases.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권9호
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• pp.3594-3610
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• 2015

Recent advancements in broadband wireless communication technologies enable mobile users to receive video streaming services with various smart devices. The long term evolution (LTE) network provides high bandwidth and low latency for several emerging mobile applications. This paper proposes the buffer aware scheduling (BAS) approach to schedule the downlink video traffic in LTE network. The proposed BAS scheme applies the weighting function to heuristically adjust the scheduling priority by considering the buffer status and channel condition of UE so as to reduce the time that UE stays in the connected state without receiving data. Both of 1080P and 2160P resolution video streaming sources were applied for exhaustive simulations to examine the performance of the proposed scheme by comparing to that of the fair bandwidth (FB) and the best channel quality indicator (CQI) schemes. The simulation results indicate that the proposed BAS scheme not only achieves better performance in power saving, streaming delivery time, and throughput than the FB scheme while maintaining the similar performance as the best CQI scheme in light traffic load. Specifically, the proposed scheme reduces streaming delivery time and generates less signaling overhead than the best CQI scheme when the traffic load is heavy.

• Journal of Information Processing Systems
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• 제13권6호
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• pp.1544-1553
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• 2017

The network coding mechanism has attracted much attention because of its advantage of enhanced network throughput which is a desirable characteristic especially in a multi-hop wireless network with limited link capacity such as the device-to-device (D2D) communication network of 5G. COPE proposes to use the XOR-based network coding in the two-hop wireless network topology. For multi-hop wireless networks, the Distributed Coding-Aware Routing (DCAR) mechanism was proposed, in which the coding conditions for two flows intersecting at an intermediate node are defined and the routing metric to improve the coding opportunity by preferring those routes with longer queues is designed. Because the routes with longer queues may increase the delay, DCAR is inefficient in delivering real-time multimedia traffic flows. In this paper, we propose a network coding-aware routing protocol for multi-hop wireless networks that enhances DCAR by considering traffic load distribution and link quality. From this, we can achieve higher network throughput and lower end-to-end delay at the same time for the proper delivery of time-sensitive data flow. The Qualnet-based simulation results show that our proposed scheme outperforms DCAR in terms of throughput and delay.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권1호
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• pp.237-252
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• 2017

In recent years, data centers have become the core infrastructure to deal with big data processing. For these big data applications, network transmission has become one of the most important factors affecting the performance. In order to improve network utilization and reduce job completion time, in this paper, by real-time monitoring from the application layer, we propose job-aware priority scheduling. Our approach takes the correlations of flows in the same job into account, and flows in the same job are assigned the same priority. Therefore, we expect that flows in the same job finish their transmissions at about the same time, avoiding lagging flows. To achieve load balancing, two approaches (Flow-based and Spray) using ECMP (Equal-Cost multi-path routing) are presented. We implemented our scheme using NS-2 simulator. In our evaluations, we emulate real network environment by setting background traffic, scheduling delay and link failures. The experimental results show that our approach can enhance the Hadoop job execution efficiency of the shuffle stage, significantly reduce the network transmission time of the highest priority job.

• 한국멀티미디어학회논문지
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• 제17권5호
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• pp.590-600
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• 2014

In the wireless sensor network environment, clustering scheme has a problem that a large amount of energy is unnecessarily consumed because of frequently occurred entire re-clustering process. Some of the studies were attempted to improve the network performance by getting rid of the entire network setup process. However, removing the setup process is not worthy. Because entire network setup relieves the burden of some sensor nodes. The primary aim of our scheme is to cut down the energy consumption through minimizing entire setup processes which occurred unnecessarily. Thus, we suggest a re-clustering scheme that considers event detection, transmitting energy, and the load on the nodes. According to the result of performance analysis, our scheme reduces energy consumption of nodes, prolongs the network lifetime, and shows higher data collection rate and higher data accuracy than the existing schemes.

• 정보처리학회논문지:컴퓨터 및 통신 시스템
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• 제3권9호
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• pp.279-292
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• 2014

에너지 절감형 서버 클러스터에서는 에너지절감을 고려하지 않는 기존 환경에서만큼의 서비스 품질을 보장하면서 전력소비를 최대로 절감하는 것이 목표이다. 에너지 절감형 서버 클러스터에 관한 기존 연구에서는 현재의 사용자요청을 처리하는데 필요한 최소한의 서버 대수를 계산하여 해당 서버만을 활성화하도록 서버 전원 모드를 일정주기마다 제어한다. 부하가 급격하게 변하는 상황에서는 서버 수를 빨리 증가하지 못하기 때문에 기존 연구에서는 서비스품질이 떨어진다. 이 문제를 해결하기 위해, 본 논문에서는 부하추세를 급증, 증가, 완만, 감소, 급감하는 5가지 상황으로 분류하여 필요한 서버 대수를 계산할 때 각 상황에 맞는 다중 임계치를 적용한다. 또한 부하추세를 5등급으로 나누는 기준을 서버가 부하를 추가로 감당할 수 있는 잔여용량에 따라 유연하게 조정하는 방법을 추가로 사용한다. 실험은 서버 15대로 클러스터를 구성하여 수행하였다. SPECweb이라는 전문 벤치마킹 툴을 이용하여 부하가 급격하게 변화하는 패턴들을 생성하여 사용하였다. 실험 결과는 서비스품질은 에너지절감을 고려하지 않는 기존의 클러스터링 방식 수준으로 향상되었으며, 소비전력은 부하 패턴에 따라 최대 약 50% 절감되었음을 보여준다.

• 한국컴퓨터정보학회논문지
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• 제19권9호
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• pp.55-63
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• 2014

무선센서네트워크(WSNs)에서 센서시스템의 한정된 에너지를 극복하기 위한 연구들이 활발하게 진행되고 있다. 이들은 대부분에너지 적응형(Energy-aware) 기법들이 많은데, 이 기법들은 노드 자신 또는 이웃노드들의 에너지양을 활용하고 있다. 그러나 기존의 센서시스템에서는 전압과 소모전류만을 가지고 잔여에너지양을 예측하고 있는데, 실제 배터리의 잔여에너지양은 온도와 로드(Load)의 영향을 많이 받기 때문에 정확하지 못할 수 있다. 본 연구에서는 배터리의 전압과 함께 배터리의 온도와 부하 특성을 반영한 효율적인 잔여에너지양 추정기법을 제안한다. 제안한 기법은 실제 환경에서의 실험과 시뮬레이션을 통해 그 성능을 검증하였다.

• Journal of Communications and Networks
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• 제17권1호
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• pp.47-57
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• 2015

With the ever growing demand of data applications, the joint macro-relay networks are emerging as a promising heterogeneous deployment to provide coverage extension and throughput enhancement. However, the current cellular networks are usually designed to be performance-oriented without enough considerations on the traffic variation, causing substantial energy waste. In this paper, we consider a joint macro-relay network with densely deployed relay stations (RSs), where the traffic load varies in both time and spatial domains. An energy-efficient scheme is proposed to dynamically adjust the RS working modes (active or sleeping) according to the traffic variations, which is called traffic-aware relay sleep control (TRSC). To evaluate the performance of TRSC,we establish an analytical model using stochastic geometry theory and derive explicit expressions of coverage probability, mean achievable rate and network energy efficiency (NEE). Simulation results demonstrate that the derived analytic results are reasonable and the proposed TRSC can significantly improve the NEE when the network traffic varies dynamically.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권1호
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• pp.22-37
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• 2013

Content distribution to a large number of concurrent clients stresses both server and network. While the server limitation can be circumvented by deploying server clusters, the network limitation is far less easy to cope with, due to the difficulty in measuring and balancing network load. In this paper, we use two useful network load metrics, the worst link stress (WLS) and the degree of interference (DOI), and formulate the problem as partitioning the clients into disjoint subsets subject to the server capacity constraint so that the WLS and the DOI are reduced for each session and also well balanced across the sessions. We present a network load-aware partition algorithm, which is practicable and effective in achieving the design goals. Through experiments on PlanetLab, we show that the proposed scheme has the remarkable advantages over existing schemes in reducing and balancing the network load. We expect the algorithm and performance metrics can be easily applied to various Internet applications, such as media streaming, multicast group member selection.