Sakae Okubo

Tree-based application layer multicast using proactive route maintenance and its implementation

The purpose of this study is to maintain efficient backup routes for reconstructing overlay trees quickly. In most conventional methods, after a node leaves the trees, its children start searching for a new parent. In this reactive approach, it takes a lot of time to find a new parent. In this paper, we propose a proactive approach to finding a new parent over the overlay trees before the current parent leaves. A proactive approach allows a node to find its new parent immediately and switch to the backup route smoothly. In our proposal, the structure of the overlay tree using a redundant degree can decide a new parent without so much overhead. Simulations demonstrate our proactive approach can recover from node departures 2 times faster than reactive approaches, and can construct overlay trees with lower overheads than another proactive method. Additionally we carried out experiments over actual networks and their results support the effectiveness of our approach. We confirmed that our proposal achieved better streaming quality than conventional approaches.

Proactive Route Maintenance and Overhead Reduction for Application Layer Multicast

The purpose of this study is to maintain efficient backup routes for restoring overlay trees. In most conventional methods, after a node leaves the trees, its children start searching for a new parent. In this reactive approach, it takes a lot of time to find a new parent. In this paper, we propose a proactive approach to find a new parent over the overlay trees before the current parent leaves. A proactive approach can find respective new parents immediately and switch to the backup route smoothly. In our proposal, the structure of the overlay tree using a redundant degree enables to decide a new parent without so much overhead information. Simulations demonstrate our proactive approach can recover from node departures 2 times faster than reactive approaches, and can construct overlay trees with lower overheads than another proactive method. Additionally we carried out experiments over actual networks and their results support the effectiveness of our approach. We confirmed that our proposal achieved better streaming quality than conventional approaches

Overlay tree construction to distribute layered streaming by application layer multicast

With the development of broadband technologies, more and more multimedia contents such as video or bulk file are being distributed over the Internet. However, an important issue to be resolved is how to construct an efficient overlay to provide users with the acceptable throughput and delay, while receiving multimedia contents. Therefore, this paper designs a tree construction algorithm by distributing the layered steaming over the ALM in order to improve both throughput and user delay. Firstly, to improve the throughput, based on theory analysis, we define a layered degree, out/in-degree and the corresponding constraints to manage the layered streaming and nodes. Secondly, a novel method, called Bi-cast, is proposed to reduce user delay during data-transmission. Thirdly, by using the defined degrees and the Bi-cast, we present a tree construction algorithm. Both the simulation and the implementation are carried out, and the results show that our proposal can obtain better performance than other conventional methods.

Strategies towards robust and stable application layer multicast

The purpose of this study is to construct a robust and stable overlay tree of ALM (Application Layer Multicast) for real-time video transmission. Firstly, we propose a proactive route maintenance which enables fast recovery of the overlay tree against node departures and failures. By forcing free node degrees for route backup, signaling overheads for route maintenance can be reduced in a scalable manner. Secondly, we improve performance of the proposed method by introducing layered video coding. Smooth layer management instead of coarse degree management contributes to reduction of the depth of overlay tree (i.e. delay) as well as to efficient bandwidth utilization. Thirdly, we introduce session records of each node into the overlay tree construction. Long-term history of user access records is expected to bring more robust overlay trees. Finally, we carried out extensive evaluation experiments. Simulations and implementations demonstrate that our methods lead to fast recovery of the overlay tree against node departures and reduction of the signaling overheads. Furthermore, introduction of layered video coding is proved to be efficient to reduce delays, to improve bandwidth utilization and to avoid severe degradation of picture quality. Final experiments show that incorporation of node stability reduces the number of nodes affected by parent node departures by promoting adequate nodes to upper layer of the ALM tree.

Application layer multicast with proactive route maintenance over redundant overlay trees

In this paper, an efficient algorithm to look for backup parents in preparation of parent leaving is proposed for application layer multicasting whose topology is constituted in the shape of a tree from a single source node. In most conventional methods, each child node starts searching for its new parent after its parent node leaves from a multicasting tree. This reactive operation often causes long interruption period. In our proposal, each node holds its parent candidate proactively over redundant overlay trees. Proactive route maintenance leads to smooth switching to a new parent after node leaving and failure, and redundant structure of a multicasting tree avoids exhausting search of a backup parent. Computer simulations are also carried out and effectiveness of the proposed approach is verified.

Proactive Route Maintenance for Tree-Based Application Layer Multicast and Its Implementations

The purpose of this study is to maintain efficient backup routes for reconstructing overlay trees quickly. In most conventional methods, after a node leaves the trees, its child nodes start searching for the new parents. In this reactive approach, it takes a lot of time to find a new parent. In this paper, we propose a proactive approach to finding a next parent as the backup route node over the overlay tree before the current parent leaves. A proactive approach allows a node to find its new parent node immediately and switch to the backup route node smoothly. In our proposal, the structure of the overlay tree using a redundant degree can decide a backup route node without so much overhead. Simulations demonstrate our proactive approach can recover from node departures 2 times faster than reactive approaches, and can construct overlay trees with lower overheads than another proactive method. Additionally we carried out experiments over actual networks and their results support the effectiveness of our approach. We confirmed that our proposal achieved better streaming quality than conventional approaches.

Efficient Construction in ALM with Assignment of Layered Degree and ALM-Bi-Cast

Application Layer Multicast (ALM) has emerged as a promising alternation to the conventional IP multicast. However, as more and more streaming media are being distributed over the ALM recently, an important issue becomes to be how to construct an efficient overly tree to achieve certain optimal objectives, including both throughput and delay [3] [4]. Layer-encoded streaming is thought to be one of the solutions to the above issue because it can be partitioned into multiple layers and distributed by different nodes from different paths. For each receiver, it is only necessary to get a subset to recovery video with an acceptable quality degradation. Therefore, this paper designs a tree construction algorithm by distributing the layered steaming over the ALM in order to improve both the throughput and user delay. Firstly, by carrying out theory analysis, we define an Out/In degree and the corresponding constraints to manage the layered streaming and nodes to improve the throughput. Besides, a novel method, called ALM-Bi-cast, is also proposed and analyzed to reduce user delay during the data-transmission. Secondly, by using the defined degrees and the ALM-Bi-cast, we present a tree construction algorithm and test it by simulations with NS-2. Simulations show that the proposal can get better results than other conventional methods. Finally, we carry out an implementation of our proposal, by distributing the video encoded by H.263+ over the ALM nodes placed in Tokyo City and Kyusyu Prefecture. Implementation further improves the out-performance of our proposal.

A High Resolution Picture Transmission System Using the Video Telephone Network

低速走査精細画像をハードコピーの形で受信する場合について検討する.まず可能な案について利害得失を論じ, 次にその中で有望と考えられるテレビ電話機の撮像管をファクシミリの送信に共用する方式に関し, 実験装置の構成と特性の測定結果を述べる.1インチビジコンを用いた実験装置の低速走査時 (水平走査周波数=500Hz, 走査線数=1024本) の特性は, 限界解像度=700TV本, SNR=20～30dB, 走査ひずみ=±3%, 階調=7～8段階であり, SNRを改善する必要がある.

Computer Simulation of Delta Modulation for Video Signals

テレビ電話信号をデルタ変調によって伝送する場合の方式パラメーターに関し, シミュレーション実験によって検討した.その結果, 固定ステップデルタ変調方式の標本化周波数は, 画像信号の帯域の少なくとも8倍は必要なこと, 可変ステップデルタ変調方式の場合, 6倍では輪郭部分に多少劣化があるが, 8倍にすれば満足できる画質の得られること, 可変ステップ方式のステップ変化規則は, 画質にはあまり影響しないこと, などが明らかになった.

Statistical Properties of Television Signals

静止画像および動画像に対するテレビ信号を実時間的に処理し, 振幅分布, 1次階差および内挿差の分布に関し測定を行なった.その結果, 振幅分布は画像の種類による依存性が強いのに対し, 1次階差および内挿差の分布は指数分布の形に従うことがわかった.この分布関数を用いると, 1次階差の電力は一様分布と仮定した原テレビ信号より20～24dB減少し, 内挿差の電力はさらに3dB減少していることが判明した.