Low Cost Quality of Service Multicast Routing in High Speed Networks

Many of the services envisaged for high speed networks, such as B-ISDN/ATM, will support real-time applications with large numbers of users. Examples of these types of application range from those used by closed groups, such as private video meetings or conferences, where all participants must be known to the sender, to applications used by open groups, such as video lectures, where partcipants need not be known by the sender. These types of application will require high volumes of network resources in addition to the real-time delay constraints on data delivery. For these reasons, several multicast routing heuristics have been proposed to support both interactive and distribution multimedia services, in high speed networks. The objective of such heuristics is to minimise the multicast tree cost while maintaining a real-time bound on delay. Previous evaluation work has compared the relative average performance of some of these heuristics and concludes that they are generally efficient, although some perform better for small multicast groups and others perform better for larger groups. Firstly, we present a detailed analysis and evaluation of some of these heuristics which illustrates that in some situations their average performance is reversed; a heuristic that in general produces efficient solutions for small multicasts may sometimes produce a more efficient solution for a particular large multicast, in a specific network. Also, in a limited number of cases using Dijkstra's algorithm produces the best result. We conclude that the efficiency of a heuristic solution depends on the topology of both the network and the multicast, and that it is difficult to predict. Because of this unpredictability we propose the integration of two heuristics with Dijkstra's shortest path tree algorithm to produce a hybrid that consistently generates efficient multicast solutions for all possible multicast groups in any network. These heuristics are based on Dijkstra's algorithm which maintains acceptable time complexity for the hybrid, and they rarely produce inefficient solutions for the same network/multicast. The resulting performance attained is generally good and in the rare worst cases is that of the shortest path tree. The performance of our hybrid is supported by our evaluation results. Secondly, we examine the stability of multicast trees where multicast group membership is dynamic. We conclude that, in general, the more efficient the solution of a heuristic is, the less stable the multicast tree will be as multicast group membership changes. For this reason, while the hybrid solution we propose might be suitable for use with closed user group multicasts, which are likely to be stable, we need a different approach for open user group multicasting, where group membership may be highly volatile. We propose an extension to an existing heuristic that ensures multicast tree stability where multicast group membership is dynamic. Although this extension decreases the efficiency of the heuristics solutions, its performance is significantly better than that of the worst case, a shortest path tree. Finally, we consider how we might apply the hybrid and the extended heuristic in current and future multicast routing protocols for the Internet and for ATM Networks.

The Second Generation in New York City: A Demographic Overview

The study analyzes the forces leading to or impeding the assimilation of a 18-32 year olds from immigrant backgrounds that vary in terms of race, language, and the mix of skills and liabilities their parents brought to the United States. To make sure that what we find derives specifically from the immigrant experience, rather than simply being a young person in New York, we are also studying a "control group" of people from native born white, black, and Puerto Rican backgrounds. The main sample is drawn from the inner part of the region where the vast majority of immigrants and native born minority group members live and grow up. Our study groups make possible a number of interesting comparisons. Unlike many other immigrant groups, the West Indian first generation speaks English, but the dominant society racially classifies them as black. We are interested in ways that their experiences resemble or differ from native born African Americans. Dominicans and the Colombian-Peruvian-Ecuadoran population both speak Spanish, but live in different parts of New York, have different class backgrounds prior to immigration, and, quite often, different skin tones. We have compared them to Puerto Rican young people, who, along with their parents, have the benefit of citizenship. Chinese immigrants from the mainland tend to have little education, while young people with overseas Chinese parents come from families with higher incomes, more education, and more English fluency. According to the 1990 Census, the base year for looking at the first generation parents, these five groups accounted for 45 percent of the immigrants who had arrived in metropolitan New York since 1970. Our ability to compare these groups with native born whites, blacks and Puerto Ricans has permitted us to analyze the effects of nativity while controlling for race and language background

Computer-based facility scheduling

Imperial Users onl

The teaching and learning research programme (TLRP) in Wales: research evidence for educational policy and practice in Wales

Alex Morgan and Jane Waters, Swansea University; Jane Williams

Warren Eugene Howell, Seventh-day Adventist Educational Administrator

Problem. Warren Eugene Howell served the Seventh-day Adventist educational system as an administrator and teacher for thirty-four years. He pioneered in two important Adventist educational institutions and led the General Conference Education Department during a critical period in the history of Seventh-day Adventist education. Notwithstanding Howell\u27s contribution to Adventist education, no comprehensive study of his administration has been attempted. Method. In this study a historical-documentary method of research has been used. Correspondence collections; minutes of boards, committees, and faculty meetings; church periodicals; transcripts of lectures; and miscellaneous archival materials have provided primary source materials. These sources may be found in the Adventist Heritage Center and Andrews University, Berrien Springs, Michigan; the Ellen G. White Research Centers in Washington, D.C., and Andrews University; the archives of the General Conference of Seventh-day Adventists, Washington, D.C.; and the archives and special collections of the Loma Linda University Libraries, Loma Linda, California. Conclusions. During Howell\u27s thirty-four years in Seventh-day Adventist education, he served as academy principal, president of two colleges, founding principal of the Fireside Correspondence School, and assistant then executive secretary of the department of education of the General Conference of Seventh-day Adventists. As academy principal, Howell faced the challenge of introducing Christian values to a non-Christian student body in a mission school setting. He promoted school growth, planned new facilities, supervised the faculty, and developed programs. In his role as college president, he fought to prevent the financial collapse of Healdsburg College, then presided over its demise. Following this experience, he pioneered in establishing the College of Evangelists, which later became Loma Linda University, one of the leading institutions in the Adventist educational system. While assistant secretary and executive secretary of the department of education, Howell promoted Adventist education, encouraged greater professional development of teachers, stimulated enrollment growth in Adventist schools, wrote prolifically for Adventist publications, and struggled with changes brought by shifting societal values and rising standards of education. As an administrator, Howell\u27s strengths were in his abilities as a promoter and builder. His greatest weakness lay in his relationships with strong subordinate administrators. Howell\u27s administrative style tended to be authoritarian but was often indecisive and hesitant, qualities which annoyed his subordinates and eventually contributed to his undoing. While Howell led the educational program of the church during a critical period of consolidation, he has been almost forgotten in the chronicles of its development