Tatsuo Nakajima

An approach for constructing mobile applications using service proxies

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.

Integrated management of priority inversion in Real-Time Mach

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. 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.<<ETX>>

Resource reservation for adaptive QOS mapping in real-time mach

In this paper, we describe an adaptive QOS mapping scheme where the QOS parameters of applications are mapped into resource requirements dynamically, and the resources for the applications are reserved based on the measured resource utilization. Real-Time Mach provides resource reservation facilities that are suitable for supporting the adaptive QOS mapping scheme, and we show the effectiveness of the resource reservation facilities when the adaptive QOS mapping scheme is adopted.

A continuous media application supporting dynamic QOS control on real-time Mach

A QOS control is one of the most important factors in continuous media applications. The QOS levels of the applications should be maintained even if several continuous media applications are running concurrently. Also, the QOS levels should be changed according to a number of applications and their respective importances when a system is overloaded. This paper presents our experience with a video-on-demand system that supports a dynamic QOS control scheme on Real-Time Mach, and shows the necessity of a real-time resource management for building such applications.

Adaptive continuous media applications in mobile computing environments

This paper presents a new framework for building continuous media applications in a mobile computing environment. In a mobile computing environment, network bandwidth and machine configurations may be changed dramatically, and mobile applications should be adapted to various operational environments for efficient execution. 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.

A processor reservation system supporting dynamic QOS control

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.

Virtual memory management for interactive continuous media applications

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 storage. 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 usage of other continuous media applications.

A dynamic QoS control based on optimistic processor reservation

The paper proposes a 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 streams quality.

Experiences with building a continuous media application on Real-Time Mach

Real-time system and continuous media system researchers have worked in areas that are considered by each to be unrelated to the others domain although continuous media system researchers agree with the effectiveness of real-time technologies on continuous media systems. Media control techniques for improving the smoothness of continuous media such as jitter control and inter-stream synchronization schemes are developed for smoothing continuous media streams running on traditional timesharing operating systems. On the other hand, real-time system researchers show the effectiveness of real-time technologies for satisfying timing constraints of the continuous media. However, there is no report to showing the effectiveness of real-time technologies for the media control techniques. This paper describes experiences with building a continuous media application on Real-Time Mach. First, we present the structure of our distributed video player, called QtPlay, and its media control techniques for smoothing continuous media streams, then we show the effectiveness of real-time technologies for the media control techniques.

Environment Server: A System Support for Adaptive Distributed Applications

Various new types of applications can be available in future computing environments such as mobile computing environments and ubiquitous computing environments. The applications may change our daily life dramatically since computers can be embedded in our daily necessaries such as televisions, microwaves, cameras, and air conditioners. In these environments, computing environments can be changed dramatically, and applications may be migrated among computers that have drastically different hardware configurations. Therefore, these applications should be adapted to various computing environments that may have dramatically different characteristics for their efficient executions, and the adaptation requires that the applications can access information about computing environments through a uniform interface.