研究者詳細 - 横平　徳美

論文 - 横平　徳美

分割表示 149 件中 81 - 100 件目／全件表示 >>

Performance evaluation of a multi-stage network event detection scheme for decreasing the false-positive rate for a large number of simultaneous, unknown events 査読

Tutomu Murase, Hiroki Fujiwara, Yukinobu Fukushima, Masayoshi Kobayashi, Tokumi Yokohira

Proceedings of the Sixth International Conference on Networking, ICN'07 2007年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Change-point detection schemes are a promising approach for detecting network anomalies, such as attacks and epidemics by unknown viruses and worms. They detect those events as change-points. However, they generally also detect false-positive change-points, those caused by other events such as hardware trouble. A scheme is needed that only detects truepositive change-points, caused by attacks and epidemics. Truepositive change-points tend to occur simultaneously in very large numbers, while false-positive change-points tend to occur sporadically. We can exclude false-positive change-points by excluding change-points that occur sporadically, based on information gathered from the entire network. In this paper, we propose a multi-stage network event detection scheme that aggregates change-point information from distributed IDSs (Intrusion Detection Systems) and detects the true-positive change-points. Simulation results show that, compared to a scheme using only one IDS, our method always yields a smaller false-positive rate under the constraint that the detection rate of the true-positive change-points must exceed 0.99. © 2007 IEEE.

DOI： 10.1109/ICN.2007.71

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High-speed calculation of worst-case link delays in the EDD connection admission control scheme 査読

Tokumi Yokohira, Kiyohiko Okayama

IEICE TRANSACTIONS ON COMMUNICATIONS E89B ( 7 ) 2012 - 2022 2006年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG

The EDD connection admission control scheme has been proposed for supporting real-time communication in packet-switched networks. In the scheme, when a connection establishment request occurs, the worst-case link delay in each link along the connection is calculated to determine whether the request can be accepted or not. In order to calculate the worst-case link delay, we must perform a check called the point schedulability check for each of some discrete time instants (checkpoints). Therefore when there are many checkpoints, the worst-case link delay calculation is time-consuming. We have proposed a high-speed calculation method. The method finds some checkpoints for which the point schedulability check need not be performed and removes such unnecessary checkpoints in advance before a connection establishment request occurs, and the check is performed for each of the remaining checkpoints after the request occurs. However, the method is not so effective under the situation that the maximum packet length in networks is large, because the method can find few unnecessary checkpoints under the situation. This paper proposes a new high-speed calculation method. We relax the condition which determines whether or not the point schedulability check need not be performed for each checkpoint in our previous method and derive a new condition for finding unnecessary checkpoints. Using the proposed method based on the new condition, we can increase the number of unnecessary checkpoints compared to our previous method. Numerical examples which are obtained by extensive simulation show that the proposed method can attain as much as about 50 times speedup.

DOI： 10.1093/ietcom/e89-b.7.2012

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Throughput Optimization for TCP with an Active Proxy in Long-Delay Satellite Environments 査読

Wang Hui, Shigeyuki Osada, Tokumi Yokohira, Yukinobu Fukushima, Deng Chaolong, Kiyohiko Okayama, Nariyoshi Yamai

2006 Joint Conference on Satellite Communications (JC-SAT 2006) 2006年

A burst assembly method for decreasing end-to-end packet delays in optical burst switching networks 査読

Yukinobu Fukushima, Tokumi Yokohira, Yasuhiro Noine, Kazuteru Nagahara

2006 10TH INTERNATIONAL CONFERENCE ON COMMUNICATION TECHNOLOGY, VOLS 1 AND 2, PROCEEDINGS 459 - + 2006年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IEEE

Although the offset-time-based scheme can differentiate packet/burst loss rate according to their QoS levels in optical burst switching networks, it increases end-to-end packet delays of packets in a burst with higher QoS level. This is because it increases offset time of bursts in proportional to their QoS levels. In this paper, we propose a burst assembly method that decreases end-to-end packet delays. Our proposed method includes packets that arrive during the offset time into the currently assembled bursts while the conventional method includes them into the burst assembled next time. Simulation results show that our method offers more than 21% delay reduction for bursts with the highest QoS level.

DOI： 10.1109/ICCT.2006.341915

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Throughput optimization in TCP with a performance enhancing proxy 査読

Shigeyuki Osada, Wang Hui, Tokumi Yokohira, Yukinobu Fukushima, Kiyohiko Okayama, Nariyoshi Yamai

2006 10TH INTERNATIONAL CONFERENCE ON COMMUNICATION TECHNOLOGY, VOLS 1 AND 2, PROCEEDINGS 392 - + 2006年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IEEE

To improve TCP throughput performance, a method using a PEP (Performance Enhancing Proxy) has been proposed. The PEP operates on a router along a TCP connection. When a data packet arrives at the PEP, it forwards the packet to the destination host, transmits the corresponding ACK (premature ACK) to the source host in behalf of the destination host, and stores a copy of the packet into its own buffer (PEP buffer) in case retransmission of the packet is required. As a congestion control method on the PEP, a method which keeps the number of prematurely acknowledged packets in the PEP buffer below a threshold (watermark) value has been proposed. However, the relation between the watermark value and throughput is not sufficiently investigated, and an optimization method of the watermark value is not proposed. In this paper, we first investigate the relation between the watermark value and the average throughput. Extensive simulations show that the simulation results are roughly classified into two cases. In the first case, the average throughput becomes larger for larger watermark values and becomes a constant value when the watermark is over a certain value. In the second case, although the average throughput becomes larger for larger watermark values in the same way, it decreases when the watermark is over a certain value. Next, based on the results about the relation, we propose an watermark optimization algorithm which can adaptively maximize the average throughput of each connection and also satisfy a fairness condition that the average throughputs of connections are equal to each other.

DOI： 10.1109/ICCT.2006.341898

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Node placement algorithms in the case that routes are design variables in shuffle-like multihop lightwave networks 査読

T Yokohira, K Okayama

IEICE TRANSACTIONS ON COMMUNICATIONS E88B ( 12 ) 4578 - 4587 2005年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG

The shuffle-like network (SL-Net) is known as a logical topology for WDM-based multihop packet-switched networks. Even if we fix the logical topology to an SL-Net, we can still reposition nodes in the SL-Net by re-tuning wavelengths of transmitters and/or receivers. In conventional node placement algorithms, routes between nodes are assumed to be given. In this paper, we propose two heuristic node placement algorithms for the SL-Net to decrease the average end-to-end packet transmission delay under a given traffic matrix in the case that routes are design variables. The principal idea is to prevent too many traffic flows from overlapping on any link. To attain the idea, in one of the algorithms, a node is selected one by one in a decreasing order of the sums of sending and receiving traffic requirements in nodes, and its placement and routes between the node and all the nodes already placed are simultaneously decided so that the maximum of the amounts of traffic on links at the moment is minimum. In the other algorithm, a node is selected in the same way, and first it is placed so that the average distance between the node and all the nodes already placed is as large as possible, and then routes between the node and all the nodes already placed are decided so that the maximum of the amounts of traffic on links at the moment is minimum. Numerical results for four typical traffic matrices show that either of the proposed algorithms has better performance than conventional algorithms for each matrix, and show that the proposed algorithms, which are based on a jointed optimization approach of node placement and routing, are superior to algorithms which execute node placement and routing as two isolated phases.

DOI： 10.1093/ietcom/e88-b.12.4578

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Node placement algorithms for shuffle-like packet-switched networks with wavelength-division multiplexing 査読

Tokumi Yokohira, Takuji Okamoto

Electronics and Communications in Japan, Part I: Communications (English translation of Denshi Tsushin Gakkai Ronbunshi) 88 ( 1 ) 72 - 81 2005年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

The shuffle-like network (SL-Net) is known as a logical topology for WDM-based multihop packet-switched networks. We propose two heuristic node placement algorithms for the SL-Net to decrease the average end-to-end packet transmission delay for a given traffic matrix. The principal idea is to prevent too many traffic flows from overlapping on any link. To attain this objective, one algorithm selects nodes one by one in decreasing order of the sums of their sending and receiving traffic requirements, and places them so that the maximum traffic in the links is minimal. The other selects nodes in the same way, and places then so that the average distance among the nodes which have already been placed is as large as possible. Numerical results for four typical traffic matrices show that either of the proposed algorithms has better performance than the conventional algorithms for each matrix. © 2004 Wiley Periodicals, Inc.

DOI： 10.1002/ecja.10184

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Performance improvement of TCP using Performance Enhancing Proxies - Effect of premature ACK transmission timing on throughput 査読

Shigeyuki Osada, Tokumi Yokohira, Wang Hui, Kiyohiko Okayama, Nariyoshi Yamai

APSITT 2005: 6th Asia-Pacific Symposium on Information and Telecommunication Technologies, Proceedings 7 - 12 2005年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IEEE

In order to improve TCP performance, a method using a PEP (Performance Enhancing Proxy) is proposed. The PEP operates on a router along a TCP connection. When a data packet arrives at the PEP, it forwards the packet to the destination host, transmits the corresponding ACK (premature ACK) to the source host in behalf of the destination host and stores the copy of the packet into its own buffer (PEP buffer) in case of the retransmission of the packet. In this paper, under the strategy which keeps the number of packets in the PEP buffer for which premature ACKs have been returned being less than or equal to a fixed threshold value (watermark value), we investigate the relation between the watermark value and the maximum throughput. Extensive simulation runs show that the simulation results are roughly classified into two cases. One case is that the maximum throughput becomes larger for larger watermark value and becomes a constant value when the watermark value is over a value. The other case is that though the maximum throughput becomes larger for lager watermark value in the same way, it reversely decreases when the watermark value is over a value. We also show that the latter (former) case is easier to occur as the propagation delay in the input side network of the PEP becomes smaller (larger) and the propagation delay in the output side network of the PEP becomes larger (smaller) and the PEP buffer capacity becomes smaller (larger).

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A multiwindow system for smooth window operations by the combination of drawing-period generation method and display-period generation method 査読

Y Sato, T Yokohira, H Kagotani, T Okamoto, Kayano, I

ELECTRONICS AND COMMUNICATIONS IN JAPAN PART II-ELECTRONICS 88 ( 1 ) 12 - 23 2005年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SCRIPTA TECHNICA-JOHN WILEY & SONS

In this paper, the authors propose a multiwindow system that can smoothly execute window operations such as moving, resizing, or scrolling by using a combination of a drawing-time composition method and display-time composition method. Memory for storing the image of the window for which the window operation is to be performed (operation target window) and memory for storing a composite image of all other windows generated by a drawing-time composition method are both established in this system. The image that is displayed on the actual screen is obtained by using a display-time composition method to combine images that were read in parallel from both of these memories to generate the multiwindow image. The authors performed a trial experiment using a 640-pixel by 480-pixel display device to verify that no flicker appeared on the display screen when updating the operation target window. From the results of this trial experiment, they suggested that smooth window operations probably can also be executed for a 1280-pixel by 1024-pixel display device. (C) 2004 Wiley Periodicals, Inc.

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A framework for mobile agent systems with the capability of preceding and following users 査読

Tokumi Yokohira, Kiyohiko Okayama, Takashi Murakami, Kayo Takarako

APSITT 2005: 6th Asia-Pacific Symposium on Information and Telecommunication Technologies, Proceedings 89 - 94 2005年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IEEE

As one of mobile agent applications, many systems which provide continuous service for users moving on a network have been proposed. In these systems, because a movement of mobile agents is performed after a user movement, users must wait for arrival of mobile agents. To reduce users' waiting time, we propose a fundamental framework for mobile agent systems where an agent can move precedently before a user movement. In our framework, it is assumed that computers are connected on a network and users with rewritable devices move on the network. The framework supports precedent movement of mobile agents based on prediction using movement history of users. Because the prediction may be wrong, the framework also provides the following movement of mobile agents. Moreover, the framework provides a recovery method of mobile agents in service in case that mobile agents disappear due to problems such as their bugs. Because we provide some APIs, via which various functions of our framework are accessed, developers of mobile agent systems can easily use our framework using the APIs. We implemented an experimental agent system using the APIs and confirmed that the framework performed correctly using the experimental system.

DOI： 10.1109/APSITT.2005.203636

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CMOS floating gate defect detection using supply current test with DC power supply superposed by AC component 査読

H Michinishi, T Yokohira, T Okamoto, T Kobayashi, T Hondo

IEICE TRANSACTIONS ON INFORMATION AND SYSTEMS E87D ( 3 ) 551 - 556 2004年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG

This paper proposes a new supply current test method for detecting floating gate defects in CMOS ICs. In the method, unusual increase of the supply current caused by defects is promoted by superposing an AC component on the DC power supply. Feasibility of the test is examined by some experiments on four DUTs with an intentionally caused defect. The results showed that our method could detect clearly all the defects, one of which may be detected by neither any functional logic test nor any conventional supply current test.

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Improvement of detectability for CMOS floating gate defects in supply current test 査読

H Michinishi, T Yokohira, T Okamoto, T Kobayashi, T Hondo

ATS 2003: 12TH ASIAN TEST SYMPOSIUM, PROCEEDINGS 406 - 409 2003年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IEEE COMPUTER SOC

We already proposed a supply current test method for detecting floating gate defects in CMOS ICs. In the method, increase of the supply current caused by defects is promoted by superposing a sinusoidal signal on the supply voltage. In this study, we propose one way to improve detectability of the method for the defects. They are detected by analyzing the frequency of supply current and judging whether secondary harmonics of the sinusoidal signal exists or not. Effectiveness of our way is confirmed by some experiments.

DOI： 10.1109/ATS.2003.1250846

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描画時合成方式と表示時合成方式の併用によるスムーズ操作が可能なマルチウィンドウシステム査読

佐藤洋一郎, 横平徳美, 籠谷裕人, 岡本卓爾, 茅野功

電子情報通信学会論文誌 2003年

シャッフル型波長分割多重方式パケット交換網におけるノード配置アルゴリズム査読

横平徳美, 岡本卓爾

電子情報通信学会論文誌 2003年

双方向マンハッタンストリートネットワークのノード配置問題に対する階層型近似アルゴリズムの提案査読

米津政隆, 舩曵信生, 木谷友哉, 横平徳美, 中西透, 東野輝夫

電子情報通信学会論文誌 2003年

A quasi-solution state evolution algorithm for channel assignment problems in cellular networks 査読

N Funabiki, T Nakanishi, T Yokohira, S Tajima, T Higashino

IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES E85A ( 5 ) 977 - 987 2002年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG

For efficient use of limited electromagnetic wave resource, the assignment of communication channels to call requests is very important in a cellular network. This task has been formulated as an NP-hard combinatorial optimization problem named the channel assignment problem (CAP). Given a cellular network and a set of call requests, CAP requires to find a channel assignment to the call requests such that three types of interference constraints between channels are not only satisfied, but also the number of channels (channel span) is minimized. This paper presents an iterative search approximation algorithm for CAP, called the Quasi-solution state evolution algorithm for CAP (QCAP). To solve hard CAP instances in reasonable time, QCAP evolutes quasi-solution states where a subset of call requests are assigned channels and no more request can be satisfied without violating the constraint QCAP is composed of three stages. The first stage computes the lower bound on the channel span for a given instance. After the second stage greedily generates an initial quasi-solution state, the third stage evolutes them for a feasible channel assignment by iteratively generating best neighborhoods, with help of the dynamic state jump and the gradual span expansion for global convergence. The performance of QCAP is evaluated through solving benchmark instances in literature, where QCAP always finds the optimum or near-optimum solution in very short time. Our simulation results confirm the extensive search capability and the efficiency of QCAP.

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A Proposal of a Quasi-Solution State Evolution Algorithm for Channel Assignment Problems 査読

N.Funabiki, T.Nakanishi, T.Yokohira, S.Tajima, T.Higashino

International Conference on Information Networking 2002 2002年

CMOS floating gate defect detection using I-DDQ test with DC power supply superposed by AC component 査読

H Michinishi, T Yokohira, T Okamoto, T Kobayashi, T Hondo

PROCEEDINGS OF THE 11TH ASIAN TEST SYMPOSIUM (ATS 02) 417 - 422 2002年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IEEE COMPUTER SOC

In this paper, we propose a new I-DDQ test method for detecting floating gate defects in CMOS ICs. In the method, unusual increase of the supply current caused by defects is promoted by superposing an AC component on the DC power supply. Feasibility of the test is examined by some experiments on four DUTs with an intentionally caused defect. The results showed that our method could detect clearly all the defects, one of which may be detected by neither any functional logic test nor any conventional IDDQ test.

DOI： 10.1109/ATS.2002.1181747

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EDDコネクション受付制御方式における最悪リンク遅延の高速導出法査読

横平徳美, 岡本卓爾

電子情報通信学会論文誌 2002年

静的及びモバイルマルチキャストルーチング問題に対する最適パス選択解法の提案査読

藤井雅和, 舩曵信生, 横平徳美, 田島滋人, 常村和史, 東野輝夫

電子情報通信学会論文誌 2002年

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