研究者詳細 - 徳田　英幸

論文 - 徳田　英幸

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Load-Sensitive Handover Scheme over Wireless Local Area Networks

Daichi Furusaka,Takeshi Iwamoto, Tomohiro Nagata, Hideyuki Tokuda

IEEE ICDCS Workshop on Wireless Networks and Mobile Computing (IWWNMC '00) D12-19 2000年04月

共著, 査読有り

This paper proposes a new load-sensitive handover scheme called LSH to manage wireless LANs. Future wireless LANs will is difficult to guarantee the network quality in current wireless LANs because of poor network resources including narrow bandwidth, high latency and high error rate. Under these conditions, mobile station should share resources efficiently. LSH utilizes information about the network load. By quantitative measurement and update messages, each base station maintains the cell information including a number of mobile stations, transmit/receive throughput and loss rate. Mobile stations in the cell overlapped area can select the most suitable cell by using cell information. It works to balance the network load of each cell.

Detection of Change in One-Way Delay for Analyzing the Path Status

Yoshito Tobe,Hiroto Aida, Yosuke Tamura, Hideyuki Tokuda

Passive and Active Measurement Workshop 2000年04月

共著

The objective of detecting the change in one-way delay is to capture a congestion signal that should be reflected to a rate control of an RTP/RTCP-type unicast stream communication. Although a packet of the RTP flow may not be lost, the delay of the flow will increase due to an increase in queuing delay at the link. Therefore, only a change in delay instead of the absolute value of delay should be obtained for the rate control. Measuring the change in delay is also significant for a path that includes an error-prone wireless link. In such a wireless link,some packet losses may be irrelevant to congestion. Therefore, congestion control depending on packet loss ratio alone results in an erroneously low rate. In this paper, we describe the design and the implementation of Estimation of Skew with Reduced Samples (ESRS). We have measured changes in delay using the scheme over a path between Keio University (Japan) and Carnegie Mellon University (U.S.), and a path between Keio University and CESAT (Spain). The variation in one-way delay obtained with ESRS is shown to include the path status of the flow.

MobileSocket: Session Layer Continuous Operation Support for Java Applications

T.Okoshi,M.Mochizuki, Y.Tobe, H. Tokuda

Proceedings Eight International Conference on Computer Communications and Networks(Cat. No.99EX370) 41 （ 2 ） 50-57 2000年02月

共著, 査読有り

This paper proposes the session layer communication continuity support for Java applications toward a continuous operation for the users. In a mobile computing environment, mobile hosts move around thedifferent network segments even during applications communicate with the remote endpoint.In such a situation, maintenance of thecommunication continuity between the applications is significant.In order to retain the communication continuity, not only the mobilitysupport but the virtual circuit continuity support is required forapplications.Existing approaches on the network, the transport and the sessionlayers do not provide the complete mobility and virtual circuitcontinuity for applications, although they require the complicatedimplementation.``MobileSocket'' is a user-level enhanced socket library written inJava, and provides the library-based session layer mobility andvirtual circuit continuity support for applications. Two mechanisms, Dynamic Socket Switching (DSS) and Application LayerWindow (ALW) enforce MobileSocket and enable the implementationsimplicity.MobileSocket applications can be used in the Java mobile applications and the agents, as well as in ordinary network applications.In this paper, after we clarify the communication continuity andexisting approaches, we present the MobileSocket design, mechanism, and evaluation results.

TCP-Rate-Probing-Based Adaptation for Continuous Media Communications

Y.Tobe,Y.Tamura, H.Tokuda

情報処理学会論文誌 41 （ 2 ） 297-311 2000年02月

共著, 査読有り

Rate control of continuous media (CM) UDP flows over the Internet should retain TCP-friendliness.Despite many efforts to create TCP-friendly algorithms,it is often difficult to adjust parameters pertaining to the algorithmsin order to achieve exact fairness with TCP flows.In this paper, we propose a scheme called TCP-Rate-Probing-Based Adaptation (TPBA).In TPBA, a CM flow intermittently changes its transport protocol to TCP to measurea TCP-exact rate, and uses the rate with UDP.We have built an experimental system with FreeBSD PCs andshown that TCP-friendly rate control can easily be achievedfor both a shorter and a longer round-trip-time connections.

A Neighbor-state Based Congestion Control Schemefor Adaptive Bandwidth Sharing

Y.Tamura,Y.Tobe, H. Tokuda

情報処理学会論文誌 41 （ 2 ） 210-221 2000年02月

共著, 査読有り

In this paper, we propose the Neighbor-state Based Queuing（NBQ）for improving the performance of flows sharing link bandwidth under various transfer protocols. Each router with NBQ　informs the next upstream router of its link status. According to the received status, NBQ dynamically sets the packet discard ratio of the non-adaptive flows. NBQ　reduces the wasted non-adaptive flows and provides available bandwidth for the adaptive flows. We have demonstrated dramatic improvements of adaptive flow's throughputusing our scheme through simulations.

Software Traffic Management Architecture for Multimedia Flows over a Real-Time Microkernel

Y.Tobe,Y.Tamura, H.Tokuda

（電子情報通信学会） E82B （ 12 ） 2116-2125 1999年12月

共著, 査読有り

Traffic management schemes such as Connection Admission Control (CAC), policing, and traffic shaping are important to provide multimedia communications with better Quality of Service (QoS). In the conventional model, admission control and policing are done at intermediate nodes, and traffic shaping is done at the edge of a network. However, QoS of communications should be defined between tasks or threads rather than between hosts. Therefore traffic management inside a host is as important as that in networks. We propose software-based traffic management architecture over a real-time microkernel. The architecture focuses on the interface between a network driver and user threads calling the driver. We categorized services of communication threads into three classes: Real-Time at Guaranteed Rate (RT-GR), Real-Time at Available Rate (RT-AR), and Best-Effort (BE). Our architecture is designed for an environment containing a mixture of these services. In the architecture, a sender periodic thread of RT-GR or RT-AR is executed such that the sending rate matches a user-specified rate. The network driver monitors the per-flow rate of injected data and discards the data if the injected rate exceeds the user-specified rate. To avoid the continuous discarding of data, the sending thread can adjust its sending rate by periodically looking at logged data concerning the rate. RT-AR service can achieve more than the specified rate when bandwidth is available. The scheme of software traffic management is effective in attaining higher throughput not only for full-duplex Ethernet but also for ATM because the difference of rate between hardware and software is reduced. In this paper, we describe the design and implementation of the software-based traffic management architecture on Real-Time Mach. The results of performance evaluations demonstrate that our traffic management scheme performs well for full-duplex Ethernet.

NBQ: Neighbor-state Based Queuing for Adaptive Bandwidth Sharing

Yosuke Tamura,Yoshito Tobe, Hideyuki Tokuda

Proceedings Seventh International Conference on Network Protocol(ICNP'99) 135-144 1999年11月

共著, 査読有り

In this paper, we propose the Neighbor-state Based Queuing (NBQ) for improving the performance of flows sharing link bandwidth under various transfer protocols. Each router with NBQ informs the next upstream router of its link status. According to the received status, NBQ dynamically sets the packet discard ratio of the non-adaptive flows. NBQ reduces the wasted nonadaptive flows and provides available bandwidth for the adaptive flows. We have demonstrated dramatic improvements of adaptive flow's throughput using our scheme through simulations.

MobileSocket: Toward Continuous Operation for Java Applications

Tadashi Okoshi,Masahiro Mochizuki, Yoshito Tobe, Hideyuki Tokuda

Proceedings IEEE 8th International Conference on Computer Communications and Networks 50-57 1999年10月

共著, 査読有り

This paper proposes'MobileSocket'which realizes session layer communication continuitysupport for Java Applications towards the continuousoperations for mobile applications. In the mobile com-putting environment where mobile hosts moves aroundthe network even during applications are communi-cating with the remote, maintenance of the commu-nication continuity between the applications is signif-icant. Not only the mobility support but the virtualcircuit continuity support is required for communi-cation continuity. Existing approaches have not pro-vided the complete communication continuity for ap-plications. 'MobileSocket'is a user-level enhancedsocket library written in Java, and provides library-based session layer mobility and virtual circuit conti-nuity support for applications. Two mechanisms, Dy-namic Socket Switching (DSS) and Application LayerWindow (ALW) were developed for MobileSocket andenable a simple implementation. MobileSocket appli-cations can be used in Java mobile applications and the agents, as well as for ordinary network applica-tions. In this paper, after we clarify the communi-cation continuity and existing approaches, we presentthe MobileSocket design, mechanism, and results ofevaluation.

ホスト透過型オブジェクト移送システムMogulの実現

中澤仁,望月祐洋，徳田英幸

情報処理学会論文誌 40 （ 6 ） 2573-2584 1999年06月

共著, 査読有り

既存アプリケーションのホスト透過的な移送を実現する, ホスト透過型オブジェクト移送モデルを提案する. 本モデルは, プロセス移送や分散ウィンドウシステムにはないプラットホーム独立性を提供し, さらにオブジェクトを単位として移送の粒度を柔軟に制御できるのが特徴である. 本研究で Java 言語によって実現したホスト透過型オブジェクト移送システム Mogul は, 既存アプリケーションコードに対する変更をともなわずに, ホスト透過的なアプリケーション移送を実現する. Mogul では, アプリケーションを移送可能オブジェクトとホスト依存オブジェクトとに動的に分離し, それらの間のメソッド呼び出しをリダイレクトする, 動的メソッドリダイレクションによって透過性を確保している. 本論文では, アプリケーション移送の実現手法を比較検討したうえで, Mogul の機能および特徴を示し, 実装と評価について報告する.

Possession System: Adaptation Support Middleware for Collaborative Multimedia Applications in Java

M.Mochizuki, H. Tokuda

Proceedings IEEE 19th International Conference on Multimedia Computing and Systems （ - ） 339-344 1999年06月

研究論文（学術雑誌）, 共著, 査読有り

Possession System is middleware which realizes a simple framework to deal with the adaptation of collaborative multimedia application. The system is based on Possession Model which provides users with a consistent view of application components, networked sensors, and distributed devices by introducing two separated abstractions: Body and Soul. The adaptation is achieved through the changes of relationships among Bodies and Souls with a simple operation named possession. The adaptation actions can be invoked both manually and automatically by monitoring the changes of the environment underlying beneath the applications. The middleware is applicable to adaptive systems in mobile and ubiquitous computing environment where unpredictable changes in available computing resources, device configuration, and geographics location frequently occure. We describe how collaborative multimedia applications using our middleware adaptively behave.

Rate Probing Based Adaptation at End Hosts

Y.Tobe,Y.Tamura, H.Nishino, H. Tokuda

IEEE Workshop on QoS Support for Real-Time Internet Applications 1999年06月

共著, 査読有り

Rate control of continuous media UDP flows over the Internet should retain TCP-friendliness.Despite many efforts to create TCP-friendly algorithms, it is often difficult to adjust parameters pertaining to the algorithms in order to achieve exact fairnesswith TCP flows. In this paper, we propose a novel scheme, Rate Probing Based Adaptation (RPBA). In RPBA, a continuous media flow intermittently changes its transport protocol to TCP to measure its available rate and uses the rate with UDP. We have built an experimental system with FreeBSD PCs and shown that TCP-friendly rate control can easily be achieved both for a shorter and a longer round-trip time connections.

通信環境に適応する動的プロトコルスタック構成モデル

戸辺義人,田村陽介，徳田英幸

電子情報通信学会論文誌 J82B （ 5 ） 783-798 1999年05月

共著, 査読有り

ネットワーク上で連続メディアの配送を行うサーバとの間で通信を行うクライアントにおいて，クライアントが接続される位置に依存して，経由するネットワークの状況に応じて通信品質に差が生じる．本論文では，ネットワークに接続されたクライアントが，サーバとの通信時のデータ配送の信頼性，スループットに応じて，通信開始時及び通信持続中の両方の場合に，フローごとにプロトコルスタックを動的に変更するDPC（Dynamic Protocol stack Configuration）モデルを提案する．更に，サーバ，クライアント間で協調してプロトコルスタックを変更するためのプロトコルとして，DPCP（Dynamic Protocol stack Configuration Protocol），及びDPCモデルに対応してsocketを拡張したdsocketを定義する．本モデルをFreeBSDに実装した計算機間を無線LAN及びインターネットで接続したシステムにおいて，ネットワークの負荷の変化に対してTCPとUDPとの間の動的変更を適用し，DPCモデル適用の有効性が示された．

EFR: Efficient Fast Retransmit Scheme for TCP in a Wireless Multiple Access

Yosuke Tamura,Yoshito Tobe, Hideyuki Tokuda

（情報処理学会論文誌） 40 （ 1 ） 46-56 1999年01月

共著, 査読有り

In this paper, we propose a new and efficient fast retransmit scheme for wireless LANs. Wireless LANs are becoming popular, and providing and efficient protocol over a wireless link is important. In our experiments with 2.4 GHz WaveLAN, the poor TCP performance observed was attributed to frequent expiration of the retransmission timer. To avoid unnecessary expiration of the retransmission timer, we propose a scheme in which fast retransmission is performed efficiently. The proposed modification only affects a TCP sender, and our version of TCP with the change is interoperable with existing TCP implementations. The change is especially effective in wireless LAN environments, where we have demonstrated dramatic improvements in throughput, 10-15%, via experiments with 2.4 GHz WaveLAN.

Reliable, Real-Time and Reconfigurable System (R3-System)

H.Tokuda,T.Hagino, N.Nishio, Y.Tobe, S.Moriai, S.Kihara, Y.Matsui, T.Okamoto, M.Mochizuki, Y.Tamura, T.Nagata, T.Iwamoto

IEEE International Workshop on Networked Appliances(IWNA) 1998年11月

共著, 査読有り

SMAF:A Framework for Future Embedded Systems

T.Kitayama,T.Nakajima, T.Watanabe, K.Gondow, I.Satoh, H. Tokuda

IEEE International Workshop on Networked Appliances(IWNA) s2-1 1998年11月

共著, 査読有り

In this paper, we describe the research topics and the goals of the Seamless Migratory Application Framework (SMAF) project. The project aims to provide the common framework for building future distributed embedded applications. In the future computing environment, various types of computers will be embedded in home and office appliances, which are connected through networks. Many kinds of application may run in variety of environment, and they need to aware and adapt to the computing environment and user preferences. The SMAF project focuses on how the applications need to execute efficiently in these environments, and we are building the SMAF system framework.

EFR: A Retransmit Scheme for TCP in Wireless LANs

Y.Tamura,Y.Tobe, H. Tokuda

Proceedomgs 23rd IEEE Annual Conference on Local Computer Network (LCN'98) 2-11 1998年10月

研究論文（学術雑誌）, 共著, 査読有り

Rate-Based QoS Control of Multiple Flows over a Real-Time OS

Y.Tobe,Y.Tamura, H. Tokuda

Proceedings IEEE Fifth International Conference on Real-Time Computing Systems and Applications (RTCSA'98), 83-90 1998年10月

共著, 査読有り

We propose a framework of Quality of Service (QoS) management inside a sending host that controls execution of sending threads in consideration of utilization of processor capacity and network bandwidth. To distinguish from flows which require only best-effort service, we call a flow which requires a specific rate of service ``reserved flow.'' To guarantee QoS of such reserved flow both in processor- and network-intensive cases in a sending host, processor capacity reserve is allocated such that the rate of each reserved flow is attained and non-conforming data are policed before they are transmitted. Processor Capacity Manager and the network device driver exchange information in a cooperative manner to support the rate adaptive allocation of processor capacity reserve.

家庭内ネットワークにおける機器制御方式

橋本幹生,寺本圭一, 斉藤健, 岡本利夫，徳田英幸

電子情報通信学会講演論文集 1998 B2-267 1998年09月

共著

TMR: Traffic Management of Segregated Flows into an Egress Link over a Real-Time Operating System

Y.Tobe,Y.Tamura, H.Tokuda

System for Programming and Applications(SPA'98) （電子情報通信学会） 1998年03月

共著

QOSの3階層指定とその翻訳を用いたセッションの単純化調停方式

西尾　信彦,徳田　英幸

情報処理学会論文誌 39 （ 2 ） 328-336 1998年02月

共著, 査読有り

マルチメディアシステムでは，新しいセッションを生成したり，連続メディアセッションが終了するときに返還される資源の再分配にセッション間の調停方式が重要である．エンドユーザはセッションのサービスの質（Quality of Service; QOS）を何KBといった厳密なメモリサイズやネットワークバンド幅を指定したくはないが，このような定量値はアドミッション制御には欠かせない．そこで，我々は3-階層化したQOS指定と層間のQOSの翻訳機構を導入してシステムが定量値を扱えるようにした．それでも，セッション間の調停には複雑で時にはNP-完全問題に相当する計算量が必要となる．そこで，QOS指定に単調性の制約をつけることによって，セッション間調停を単純化し実装運用が可能になった．本論文では，Real-Time Mach 3.0上の Conductor/Performerシステムを用いて，QOSの翻訳と複数セッション間調停の実装を報告する．

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