On-board closed-loop congestion control for satellite based packet switching networks

NASA LeRC is currently investigating a satellite architecture that incorporates on-board packet switching capability. Because of the statistical nature of packet switching, arrival traffic may fluctuate and thus it is necessary to integrate congestion control mechanism as part of the on-board processing unit. This study focuses on the closed-loop reactive control. We investigate the impact of the long propagation delay on the performance and propose a scheme to overcome the problem. The scheme uses a global feedback signal to regulate the packet arrival rate of ground stations. In this scheme, the satellite continuously broadcasts the status of its output buffer and the ground stations respond by selectively discarding packets or by tagging the excessive packets as low-priority. The two schemes are evaluated by theoretical queuing analysis and simulation. The former is used to analyze the simplified model and to determine the basic trends and bounds, and the later is used to assess the performance of a more realistic system and to evaluate the effectiveness of more sophisticated control schemes. The results show that the long propagation delay makes the closed-loop congestion control less responsive. The broadcasted information can only be used to extract statistical information. The discarding scheme needs carefully-chosen status information and reduction function, and normally requires a significant amount of ground discarding to reduce the on-board packet loss probability. The tagging scheme is more effective since it tolerates more uncertainties and allows a larger margin of error in status information. It can protect the high-priority packets from excessive loss and fully utilize the downlink bandwidth at the same time

Social Movement Strategies in Human Service Delivery: the Dilemmas of a Community-Based Service Organization.

As human service organizations have become large and bureaucratic, their members typically become professionalized and assume rigid and narrowly specialized roles. Community-based organizations have tried to alter this trend by providing personal and individualized services to clients in the context of general social change goals. Unfortunately, the literature on these organizations indicates that they have many problems--notably, the loss of the community or social change orientation. This study reveals circumstances in which variations in that outcome occur. This study examines WOMAN (Women's Organization Moving Against Alcoholism and Narcotics), an organization in Detroit having both human service oriented (HSO) members interested in drug treatment services for women and social movement oriented (SMO) members interested in a community organization for poor and working class women. The study uses participant observation methods, supplemented by systematic surveys, interviews, and analysis of organizational records. It examines the relationship between these two groups from 1974 to 1977, when the community organization received federal funding to deliver drug treatment services. To trace their relationship, the dependence of each group on the other is described in detail and analyzed for six periods. Changes in the relationship are described and possible causes are cited. The findings reveal that the SMO members survived and , in some respects, dominated the HSO members. Two reasons for this outcome are proposed. One is the SMO members' ability to control the dependency of HSO members in critical areas, particularly by having some fundable ideas for the service delivery program. A second reason is the SMO members' network with other social movement groups which could provide support for the work at WOMAN. Although they did survive, SMO members did not achieve all their goals. This can be explained in part by HSO members' control of some critical resources and by the constraints of SMO members' ideology, including a belief in collectivity which limited their ability to acquire power. The roles of resource control, ideology, and the environment in dependency between HSO and SMO members are highlighted.Ph.D.SociologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/159006/1/8224964.pd

Connectivity monitoring in mobile packet radio networks

Thesis (Elec.E)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1979.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.Includes bibliographical references.by Michael Gene Hluchyj.Elec.

Multiple access communication : the finite user population problem

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1982.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.Bibliography: leaves 139-142.by Michael Gene Hluchyj.Ph.D