Browsing by Author "Chang, DW"

Now showing 1 - 7 of 7

A secure disk system: Using file system level knowledge for disk data protection
(2005)
Tsai, DS
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Chang, DW
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Chang, RC
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資訊工程學系
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Department of Computer Science
When the system is attacked and the privilege of the administrator is gained by the intruder, some important system files mail be tampered with or destroyed. In this paper, we propose a secure disk system called SecDisk, which is embedded in a disk and utilizes the knowledge of how the file system above is using the disk to protect on-disk data from intrusions. When the host system violates the access rules for the data, the administrator will be notified and the original data can be backed tip by the disk. This is beneficial since it can protect important data even when the host system is compromised. According to the experimental results, the overhead is acceptable during normal operation.
Adaptive-level memory caches on World Wide Web servers
(2000-03-01)
Chang, DW
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Ke, HR
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Chang, RC
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交大名義發表
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資訊工程學系
Owing to the fast growth of World Wide Web (WWW), web traffic has become a major component of Internet traffics. Consequently, the reduction of document retrieval latency on WWW becomes more and more important. The latency can be reduced in two ways: reduction of network delay and improvement of web servers' throughput. Our research aims at improving a web server's throughput by keeping a memory cache in a web server's address space. In this paper, we focus on the design and implementation of a memory cache scheme. We propose a novel web cache management policy named the adaptive-level policy that either caches the whole file content or only a portion of it, according to the file size. The experimental results show three things. First, our memory cache is beneficial since, under our experimental workloads, the throughput improvement can achieve 32.7%. Second, our cache management policy is suitable for current web traffic. Third, with the increasing popularity of multimedia files, our policy will outperform others currently used in WWW. (C) 2000 Elsevier Science B.V. All rights reserved.
EJVM: an economic Java run-time environment for embedded devices
(2001-02-01)
Chang, DW
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Chang, RC
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資訊工程學系
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Department of Computer Science
As network-enabled embedded devices and Java grow in their popularity, embedded system researchers start seeking ways to make these devices Java-enabled. However, it is a challenge to apply Java technology to these devices due to their shortage of resources. In this paper, we propose EJVM (Economic Java Virtual Machine), an economic way to run Java programs on network-enabled and resource-limited embedded devices. Espousing the architecture proposed by distributed JVM, we store all Java codes on the server to reduce the storage needs of the client devices. In addition, we use two novel techniques to reduce the client-side memory footprints: server-side class representation conversion and on-demand bytecode loading. Finally, we maintain client-side caches and provide performance evaluation on different caching policies. We implement EJVM by modifying a freely available JVM implementation, Kaffe. From the experiment results, we show that EJVM can reduce Java heap requirements by about 20-50 % and achieve 90 % of the original performance. Copyright (C) 2001 John Wiley & Sons, Ltd.
HANet: a framework toward ultimately reliable network services
(2005-12-01)
Jiang, YJ
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Chang, DW
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Chang, RC
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資訊工程學系
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Department of Computer Science
High availability is becoming an essential part of network services because even a little downtime may lead to a great loss of money. According to previous research, network failure is one of the major causes of system unavailability. In this paper, we propose a framework called HANet for building highly available network services. The main goal of HANet is to allow a server to continue providing services when all its network interfaces to the outside world (i.e., public interfaces) have failed. This is achieved by two techniques. First, a network interface can be backed up not only by other public network interfaces, but also by other inter-server I/O communication interfaces (i.e., private interfaces) such as Ethernet, USB, RS232, etc. Therefore, IP packets can still be transmitted and received via these I/O links, even when all of the public network interfaces have failed. Second, HANet allows a server to take over the packet transmission job of another network-failed server. The benefit of HANet is that a network-failed server will not lose any requests which are being processed. And, it is efficient since no synchronization overhead or replaying process is required. Moreover, it is totally transparent to server applications and clients. To demonstrate the feasibility of HANet, we implemented it in the Linux kernel. According to the performance results, using a private Fast Ethernet interface for data communication leads to only 1% overhead in user-perceived latency when the public Fast Ethernet interface of the server has failed. This indicates that HANet is efficient, and hence is feasible for commercial network services. (c) 2004 Elsevier Inc. All rights reserved.
Interference mitigation techniques in a high bandwidth Bluetooth access point
(2003)
Tsai, JJ
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Chang, DW
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Chang, RC
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資訊工程學系
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Department of Computer Science
Bluetooth is an emerging wireless technology over the past three years. It not only provides interconnectivity between small devices, but also makes Internet access for handheld devices possible. Due to the low data rate of Bluetooth, it is required to host multiple Bluetooth modules in a single Bluetooth access point. However, the inter-module interference would degrade the system throughput. In this paper we propose two techniques, Sequential Clock-Initialization and Address Selection, to mitigate the inter-module interference. According to the simulation results, our techniques can have performance improvements of 26% and 116% comparing to the systems without using any interference-mitigation approaches.
OS portal: an economic approach for making an embedded kernel extensible
(2003-07-15)
Chang, DW
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Chang, RC
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資訊工程學系
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Department of Computer Science
With the rapid development of embedded system techniques and Internet technologies, network-enabled embedded devices have grown in their popularity. One critical design trend of such devices is that they are shifting from static and fixed-function systems to more dynamic and extensible ones, which are capable of running various kinds of applications. To support the diversity of the applications, kernels on these devices must be extensible. However, making embedded kernels extensible is challenging due to the shortage of resources on these devices. In this paper, we propose the operating system portal framework, which makes embedded kernels become extensible while keeping the added overheads minimal. By storing kernel modules on a resource-rich server and loading them on demand, the need for equipping a local storage on the device is eliminated. In addition, we propose mechanisms for reducing the memory requirements and performing on-line module replacement on the embedded devices. According to the performance evaluation, our approach requires only 1% of the resource requirements, compared to the traditional approaches. This allows our framework to be applied on a wide range of embedded devices. (C) 2002 Elsevier Science Inc. All rights reserved.
RPC-news: a real-time, personalized, Chinese news system
(1997)
Chang, DW
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Chen, IC
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Ke, HR
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Chang, RC
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交大名義發表
With the speedy growth of information quantity, people need a mechanism to discover automatically the information that interests them. Such a mechanism is called selective dissemination of information (SDI). Describes the design and implementation of an SDI system with the ability of delivering real-time, personalized news articles. In addition to delivering English news, it delivers Chinese articles also. Focuses on the problems that other researches seldom address. First, discusses how to store and delete news articles efficiently, then describes the user model to let users specify their interests. Finally, presents an efficient method to embed the ability to deliver Chinese as well as English news articles in the system.