Conference Paper 1997 IEEE : Institute of Electrical and Electronics Engineers
Adaptive continuous media applications in mobile computing environments(First author)
モバイルコンピューティング環境における適応型連続メディアアプリケーション
Tatsuo Nakajima, Akihiro Hokimoto
【抄録】This paper presents a new framework for building continuous media applications in mobile computing environment. In mobile computing environment, network bandwidth and machine configurations may be changed dramatically, and mobile applications should be adapted to various operational environments for being executed efficiently. In our framework, an application is partitioned into two pieces. One piece runs on a mobile computer such as a notebook computer and a PDA, and another piece runs on a stationary computer. They are connected by several types of wireless networks that can be replaced at any time while applications run. The piece on a stationary computer is called a service proxy. The service proxy filters or caches data from servers on the Internet before transmitting the data to the piece on a mobile computer. These two pieces are constructed by composing small objects. The composition of objects can be dynamically reconfigured by adding or removing replaceable devices transparently from users.
Conference Paper 1997 IEEE : Institute of Electrical and Electronics Engineers
Virtual memory management for interactive continuous media applications(First author)
インタラクティブな連続メディアアプリケーションのための仮想メモリ管理
Tatsuo Nakajima, Hiroshi Tezuka
【抄録】This paper proposes a virtual memory management system suitable for interactive continuous media applications. Interactive continuous media applications usually require a large amount of memory for storing their code, data, and stack segments. In traditional operating systems, demand paging makes it possible to execute such large applications by storing most pages in secondary disks. However, continuous media applications should avoid page faults for ensuring timing constraints of continuous media since it takes a long time to swap pages between physical memory and secondary storages. Thus, it is difficult to satisfy timing constraints of continuous media. Therefore, some operating systems provide memory wiring primitives that enable applications to wire pages in physical memory by specifying the range of virtual address spaces explicitly. On the other hand, our virtual memory management system enables continuous media applications to reserve physical memory for allocating pages as soon as possible when the applications require the pages. The system implicitly and incrementally allocates and wires pages used for processing timing critical media data. Also, our system supports applications that adapt the amount of wired memory to the memory usages of other continuous media applications.
Conference Paper 1997 IEEE : Institute of Electrical and Electronics Engineers
Toolkit for building continuous media applications(Single author)
継続的メディアアプリケーション構築のためのツールキット
Tatsuo Nakajima
【抄録】Multimedia computing has emerged in the last few years as a major area of computer science. However, multimedia programming is very hard since programmers need to take into account many complex facilities such as real-time processing, media synchronization, and dynamic QOS control. Since usual programmers take a long time to understand these facilities, multimedia toolkits that can hide such complex facilities from programmers should be provided for making multimedia programming easier. The toolkit should also provide mechanisms for implementing large continuous media applications. Especially, programmers may expect to reuse existing applications for building their applications quickly. If continuous media applications can be constructed by composing a small number of big modules, programmers can create continuous media applications very quickly. In this paper, we describe a continuous media toolkit that has been developing at Multimedia and Mobile Computing Group at Japan Advanced Institute of Science and Technology. The continuous media toolkit has the following two characteristics. Application programmers do not need to take into account real-time processing, media synchronization, and dynamic QOS control since the continuous media toolkit hides such complexities from programmers. The toolkit provides a scripting language that enables programmers to reuse existing programs. Thus, programmers can create multimedia applications by modifying a small part of existing programs. Our toolkit is implemented on Real-Time Mach Microkernel. Currently, several continuous media applications are created for demonstrating the effectiveness of our toolkit.
Conference Paper 1996 IEEE : Institute of Electrical and Electronics Engineers
Dynamic QoS control based on optimistic processor reservation(Single author)
楽観的プロセッサ予約に基づく動的QoS制御
Tatsuo Nakajima
【抄録】This paper proposes a new dynamic QOS control scheme using a processor reservation system. In our scheme, a system allocates processor capacity for each application, then the application increases or decreases the current resource usage by using a feedback mechanism. This scheme allows the application to reserve resources optimistically. This means that a system can allocate all processor resources to respective applications every time. Our approach makes it easy to build a continuous media application with a dynamic QOS control scheme, and allocates processor capacity very efficiently without unexpected degradation of a media stream's quality.
Conference Paper 1996 IEEE : Institute of Electrical and Electronics Engineers
Approach for constructing mobile applications using service proxies(Last author)
サービスプロキシーを用いたモバイルアプリケーション構築のためのアプローチ
Akihiro Hokimoto, Kuniaki Kurihara, Tatsuo Nakajima Proceedings - International Conference on Distributed Computing Systems
【抄録】In this paper, we propose software architecture using a notion of service proxies, that is a new framework for constructing applications in mobile computing environment. Our framework especially takes into account applications accessing services on Internet such as WWW browsers and MBONE conference tools. In our framework, an application is partitioned into two pieces, one piece runs on a mobile computer, and another piece runs on a stationary computer, where they are connected by wireless networks that may be replaced on the fly. The piece on a stationary computer is called a service proxy. The service proxy filters or caches data from servers before transmitting the data to the piece on a mobile computer. These two pieces are constructed by composing small objects whose composition can be dynamically reconfigured by adding or removing replaceable devices. The paper also presents a toolkit using our framework for building mobile applications easily.
Conference Paper 1996 IEEE : Institute of Electrical and Electronics Engineers
Continuous media storage system supporting VBR streams(First author)
VBRストリームに対応した連続メディアストレージ・システム
Tatsuo Nakajima, Hiroshi Tezuka
【抄録】In this paper, we describe a continuous media storage system that supports the constant frame rate retrieval with variable bit rate streams. The novel characteristics of our storage system is the followings. The utilization of disk bandwidth is higher than traditional continuous media storage systems since the admission test of our storage system adopts average bandwidth usages of respective streams by introducing a novel media scaling technique in order to avoid degrading the quality of a media stream significantly when the total bandwidth exceeds 100%. Our storage system takes into account dynamic QOS control schemes. Also, it controls QOS values of respective streams according to their contents. First, we describe a media scaling technique for realizing the above characteristics, and present its scheduling algorithm and disk layout policy. Also, we present some results demonstrating the effectiveness of our approach.
Conference Paper 1996 IEEE : Institute of Electrical and Electronics Engineers
Experiences with adaptive QOS mapping scheme(First author)
Experiences with adaptive QOS mapping scheme
Tatsuo Nakajima, Hiroshi Fujita
【抄録】In multimedia computing, guaranteeing Quality of Service(QOS) is one of the most important topics. If QOS values specified by users are not ensured, the users may not put up with the degraded quality of media streams. However, operating systems cannot understand QOS values specified by users directly, then the QOS values should be mapped to the CPU capacity that is required for guaranteeing the QOS values. There are two approaches for realizing the mapping. In the first approach called static mapping, the mapping is calculated before applications are started. In the second approach called dynamic mapping, the mapping is calculated at run-time. The system monitors the actual CPU utilization of continuous media applications, and adjusts their reserved CPU resources at run-time. The advantage of the approach is that it does not require to estimate the CPU utilization that each application requires. In this paper, we propose an adaptive QOS mapping scheme using a feedback control. Also, we show that high level QOS values can be adjusted according to the reserved CPU capacity by using our algorithm.
Conference Paper 1995 IEEE : Institute of Electrical and Electronics Engineers
Processor reservation system supporting dynamic QOS control
動的QOS制御をサポートするプロセッサ予約システム
Hiroshi Fujita, Tatsuo Nakajima, Hiroshi Tezuka
【抄録】Quality of service(QOS) is one of the most important factors in multimedia computing. Future continuous media applications should guarantee their QOS values provided by users, and support dynamic QOS control schemes by changing the QOS values according to system load. A processor reservation system developed in CMU is suitable for guaranteeing QOS, but it is not appropriate to support an application with a dynamic QOS control scheme. In this paper, we describe a new processor reservation system which is suitable for dynamic QOS control schemes. It consists of two components: user-level admission server and kernel support. The user-level admission server negotiates processor resources among applications, and the kernel support notifies the malicious use of processor resource by applications.
【抄録日本語訳】マルチメディアコンピューティングにおいて、QOS(Quality of Service)は最も重要な要素の1つである。今後の連続メディアアプリケーションは、ユーザから提供されたQOS値を保証し、システム負荷に応じてQOS値を変化させる動的なQOS制御方式をサポートする必要がある。CMUで開発されたプロセッサ予約システムは、QOSの保証には適しているが、動的なQOS制御方式を持つアプリケーションをサポートするには適切ではない。本論文では、動的なQOS制御方式に適した新しいプロセッサ予約システムを説明する。このシステムは,ユーザレベルのアドミッション・サーバとカーネル・サポートの 2 つのコンポーネントから構成される.ユーザレベルのアドミッション・サーバはアプリケーション間のプロセッサ資源の交渉を行い,カーネルサポートはアプリケーションによるプロセッサ資源の悪意ある使用を通知する.
Conference Paper 1993 IEEE : Institute of Electrical and Electronics Engineers
Integrated management of priority inversion in Real-Time Mach(First author)
【抄録】Synchronization and communication are two common sources of priority inversion which may make the behavior of systems unpredictable and unanalyzable. In microkernel-based systems, they are heavily used for building operating system servers and decomposing applications into several tasks. The management of priorities in IPC and synchronization should be integrated using a uniform mechanism since priority inversion occurs if such integration is not supported. Also, a highly preemptable server structure should be provided because the execution in a server may take up too much time. In this paper, we propose an integrated real-time resource management model, and a real-time server model which solve the above problems. We implemented and evaluated the models in Real-Time Mach using a uniform mechanism. Our approach enables us to build operating system servers and to decompose applications into several tasks without incurring priority inversion.