• 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.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.38 no.6
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• pp.1-10
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• 2001

In this paper, we propose a synchronous reservation protocol that is efficient for supporting variable sized messages in a wavelength division multiplexing (WDM) based local network using a passive star topology. A. control channel is used to coordinate transmission on data channels. Time is slotted with fixed-sized slots. The network can accommodate a variable number of nodes, and can operate independently of the change of the number of nodes. So, any 'new' node can join the network anytime without network re-initialization. Moreover, with the protocol, we can avoid data channel and destination conflicts. We analyze the performance by using EPA method according to the variation of the end to end propagation delay with respect to one slot time, and validate the results by simulation.

• Journal of Korea Society of Industrial Information Systems
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• v.10 no.3
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• pp.48-56
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• 2005

This paper proposes a dynamic end-to-end flow control algorithm that is more effective than previous methods considering either the Rate of Packet Loss (RPL) or Round Trip Time (RTT). When the RPL is under normal conditions, the current network status will be in one of three defined states by using the RTT and this makes bandwidth control precise before serious packet loss occurs. If the RPL exceeds a critical level, then the network is considered to be in a fourth state. Suitable transmission rates are determined depending on the network status and are controlled by adjusting not only the number of transmitted frames but also the quality of the frames. In this paper, we present some experimental results of the proposed algorithm. According to our quantitative analysis, the proposed method performs 1.6 to 6 times better than the previous method in terms of the RPL. At the same time, the total number of transmitted packets is increased, which indicates that the proposed method can provide greater bandwidth capacity than previous methods.

• The KIPS Transactions:PartC
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• v.13C no.3 s.106
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• pp.353-358
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• 2006

Unlike TCP Reno, TCP Vegas recognizes network congestion through the measuring of RTT (Round Trip Time) and decides the main congestion control parameters, such as Windows size. But, congestion avoidance scheme of Vegas poorly reflects asymmetric characteristics of packet path because TCP Vegas uses the measuring of RTT that reflects forward/backward packet transmission delay as a forward delay. The RTT can't infer the forward/backward transmission delay variation because it only measures the packet's turn around time. In this paper, We have designed and implemented a new Vegas congestion control algorithm that can distinguish forward/backward network congestion. We have modified the source codes of TCP Vegas in Linux 2.6 kernel and verified their performance.

• Journal of Advanced Navigation Technology
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• v.12 no.2
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• pp.154-163
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• 2008

In a mobile broadband wireless access (MBWA) network, many users access a base station (BS), which relays data transferred from high-speed wired network to low-speed wireless network. For this difference of their data rate, a BS suffers from the lack of its buffer space when many users run multiple applications at the same time, and thus packet losses occur. TCP, which guarantees end-to-end reliability, is used as transport protocol also in wireless networks. But TCP lowers their transmission rate incorrectly and frequently whenever packet losses occur. And they increase their transmission rate differently with each other; finally TCP throughput of each TCP flow varies largely, and then TCP fairness goes worse. In this paper, a scheme that controls packet transmission rate adaptively according to TCP flows' transmission rate, that prevents buffer overflows at BS, and that guarantees TCP fairness at a certain degree is proposed. As it is analyzed by simulations, the proposed scheme enhances TCP fairness by maintaining TCP throughput of each TCP sender similarly with each other.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.6
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• pp.203-210
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• 2013

Majority of the wireless ad hoc routing protocols are proposed to find feasible routes without considering the network load, end-to-end link quality and bandwidth requirements of the application. Therefore, protocol may not provide sufficient quality of service (QoS) to a high speed traffic such as multimedia. In this paper, we propose a path-quality and bandwidth-estimation based routing protocol (PBBR) for the high quality multimedia stream that can meet the application's bandwidth requirements and find the best reliable route. The novelty of this protocol is to select a reliable path to respond the application's requirements based on available bandwidth at each intermediate node and end-to-end path loss ratio. Obtained results from the simulation demonstrates that our protocol can achieve sufficient performance in terms of throughput and end-to-end delay.

• Journal of KIISE
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• v.44 no.1
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• pp.107-113
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• 2017

Real-time multicasting is a packet transmission scheme ensuring that multiple destinations receive a packet within the desired time line. In wireless sensor networks, a packet can be delivered to a limited distance under a given deadline, since the end-to-end delay tends to be proportional to the end-to-end physical distance. Existing real-time multicasting protocols select the distance between the source and the furthest destination as the distance limitation and construct a multicasting tree guaranteeing delivery paths to each destination within the distance limitation. However, the protocols might lead to real-time delivery failures and energy efficiency degradation due to the fixed distance limitation. In this study, we proposed a real-time multicasting protocol using time deadline. The proposed protocol obtains the maximum transmittable distance with a given time deadline and subsequently constructs a multicasting tree using the maximum transmittable distance. The form of the multicasting tree varies according to the given time deadline to trade off the energy efficiency against the real-time delivery success ratio. The simulation results showed that the proposed scheme is superior to the existing protocols in terms of energy efficiency and real-time delivery success ratio under various time deadlines.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.7B
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• pp.550-556
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• 2008

Swam intelligence refers that a large group of simple and unsophisticated entities work together to achieve complex and significant tasks. Researches using such swarm intelligence has been performed in the network routing area. Expecially, it has been well known that routing in mobile ad-hoc networks whose features are dynamic topology and routing based on the local information is one of the applications of swarm intelligence. In this paper, we propose an ant-based routing method for MANET. The proposed method sets its goals to reduce overheads by managing ants efficiently, and to reduce route set up time. The results obtained from simulations proved that the proposed method provides shorter path set-up time and end-to-end delay and less overhead while providing comparable packet delivery ratio.

• Proceedings of the Korean Information Science Society Conference
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• 2005.07a
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• pp.595-597
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• 2005

현재 IP 멀티캐스트의 도입의 지연으로, 기존의 유니캐스트 망 기반 멀티캐스트의 필요성이 대두되어 오버레이(Overlay) 멀티캐스트 관련 연구가 진행 중이다. 특히, 확장성 제공과 작은 오버헤드 등으로 효율적인 CBT(Core Based Trees) 기반의 오버레이 멀티캐스트에 대한 연구가 활발히 진행 중이다. 그러나 기존의 거리 매트릭(Metric) 기반의 CBT로 오버레이 트리를 구성하는 경우, 특정 라우터에 패킷이 집중되는 현상으로 인하여 혼잡이 발생하여 멀티캐스트 성능 저하뿐만 아니라 네트워크 전체 성능을 저하시킬 수 있다. 본 논문에서는 이를 해결칠기 위하여. 코어 노드를 기준으로 이웃하는 두 노드 간의 패킷 중계 방향성을 계산하는 알고리즘을 제안하고. 이 결과값을 이용하는 새로운 매트릭 기반의 CBT를 구성하고자 한다. 실험 결과, CBT 상의 자식 위치에 있는 종단 노드로 패킷을 중계하는 과정에서 중복되는 패킷 전송 경로를 최소화하여 CBT를 구성함으로써 특정 라우터에 집중되는 트래픽을 줄이거나 다른 라우터로 트래픽을 분산함으로써 혼잡 발생 가능을 낮추어 보다 안정적인 통신을 기대할 수 있다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.10a
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• pp.787-790
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• 2015

Recently, M2M (Machine to Machine) communication is possible the development of MTC (Machine Type Communication) devices becomes active. MCT devices in the form of home appliances have a low power consumption, low cost, short-range wireless communication in wireless home network. For purpose, MTC devices based on IEEE 802.15.4/Zigbee are composed in the form of cluster-tree topology, which consists of one PAN (Personal Area Network), one or other router and end of nodes. It happens that transmission delay, packet drop, and lacking data resulted from collision originated by a competition for allocating channels among MTC devices that greatly increased. At last performance of entire network can be degradated. This paper proposes that the beacon frame-based grouping algorithm using multiple channels in a MTC devices in the presence of wireless home network interference. The proposed algorithm decreases the transmission delay, dropped packet and throughput is more increase, so the proposal algorithm is more efficient than the IEEE 802.15.4/ Zigbee standard.