A video-on-demand (VOD) server needs to store hundreds of movie titles and to support thousands of concurrent accesses. This, technically and economically, imposes a great challenge on the design of the disk storage subsystem of a VOD server. Due to different demands for different movie titles, the numbers of concurrent accesses to each movie can differ a lot. We define access profile as the number of concurrent accesses to each movie title that should be supported by a VOD server. The access profile is derived based on the popularity of each movie title and thus serves as a major design goal for the disk storage subsystem. Since some popular (hot) movie titles may be concurrently accessed by hundreds of users and a current high-end magnetic disk array (disk) can only support tens of concurrent accesses, it is necessary to replicate and/or stripe the hot movie files over multiple disk arrays. The consequence of replication and striping of hot movie titles is the potential increase on the required number of disk arrays. Therefore, how to replicate, stripe, and place the movie files over a minimum number of magnetic disk arrays such that a given access profile can be supported is an important problem. In this paper, we formulate the problem of the video file allocation over disk arrays, demonstrate that it is a NP-hard problem, and present some heuristic algorithms to find the near-optimal solutions. The result of this study can be applied to the design of the storage subsystem of a VOD server to economically minimize the cost or to maximize the utilization of disk arrays.

Distance education, e-learning, and virtual university are similar terms for a trend of modern education. It is an integration of information technologies, computer hardware systems, and communication tools to support educational professionals in remote teaching. This chapter presents an overview of distance education from the perspective of policy, people, and technology. A number of questions frequently asked in distance learning panel discussions are presented, with the suggested answers from the authors. The survey presented in this chapter includes communication, intelligent, and educational technologies of distance education. Readers of this 2 Shih, Hung, Ma, and JinWith the growing popularity of multimedia and Internet technologies, distance education programs have become popular and thus, importance of the related technologies are realized by educational professionals and information technology researchers. However, distance education is not totally new. The use of computer and information technologies in education has a long history. Ever since Thomas Edison predicted that motion pictures would replace textbooks for learning in 1922, the use of video was popular in training. Especially, in the World War II, the U.S. Army used video tapes to train employees. Shortly after WWII, video technology and television were used for training and demonstration. In this period, instruction was broadcasted in a single direction. There is no interaction between audiences and the instructor. However, the advantage is, the number of participants to the program can be larger than the traditional classroom education, especially when satellite communication was integrated with video broadcasting. Efficiency of video training was the first reason for education to use modern technology. The use of computers follows video technology as the second phase of modern education. Computer-based training (CBT) and computer-assisted instruction (CAI) use information technologies and educational theory to develop interactive software. The solution allows students to interact with their instructor (i.e., a computer) in a limited way. Mostly, CBT was limited to drill and practice. However, CBT and CAI were the first attempt to use computers for teaching, which enrich a new instruction delivery style -the automation. In spite of this advantage, CBT and CAI software had a problem in the '70s and the '80s -lack of stability. In that stage, computer hardware, operating systems, and system programs evolved dramatically and quickly. A CBT program is hardly used for several years due to the change of its supporting environments. Stability was a main consideration for computer-based modern education. Since the early '90s, the third period of modern education was stimulated by the invention of multimedia and Internet technologies. Multimedia presentations as CD ROM titles for education, Web-based distance-learning programs, and even online video conferencing based on ISDN, ADSL, and broadband communication channels became popular. With the new mil...

This paper presents a multilevel reversible data hiding method based on histogram shifting which can recover the original image losslessly after the hidden data has been extracted from the stego-image. The method of prediction is adopted in our proposed scheme and prediction errors are produced to explore the similarity of neighboring pixels. In this article, we propose two different predictors to generate the prediction errors, where the prediction is carried out using the center prediction method and the JPEG-LS median edge predictor (MED) to exploit the correlation among the neighboring pixels. Instead of the original image, these prediction errors are used to hide the secret information. Moreover, we also present an improved method to search for peak and zero pairs and also talk about the analogy of the same to improve the histogram shifting method for huge embedding capacity and high peak signal-to-noise ratio (PSNR). In the one-level hiding, our method keeps image qualities larger than 53 dB and the ratio of embedding capacity has 0.43 bpp (bit per pixel). Besides, the concept with multiple layer embedding procedure is applied for obtaining high capacity, and the performance is demonstrated in the experimental results. From our experimental results and analytical reasoning, it shows that the proposed scheme has higher PSNR and high data embedding capacity than that of other reversible data hiding methods presented in the literature.

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