Push and Pull Systems

Data broadcasting has emerged as an efficient way for the dissemination of information over asymmetric wireless environments where the needs of the various users of the data items are usually overlapping. In such environments, data broadcasting stands to be an efficient solution since the broadcast of a single information item is likely to satisfy a possibly large number of users. Communications asymmetry is due to a number of facts, the most important being equipment, network, and application asymmetry. This chapter starts with a discussion of preliminary issues and terminology for asymmetric environments for data broadcasting. The chapter then discusses broadcast schedule construction for systems employing a single broadcast channel, schedule construction for systems employing multiple broadcast channels, and schedule construction for systems that take into account the effect of reception errors. It then presents an 2 Nicopolitidis, Papadimitriou, & Pomportsis Copyright © 2005, Idea Group Inc. Copying or distributing in print or electronic forms without written permission of Idea Group Inc. is prohibited. algorithm that tries to provide better support for clients whose access patterns deviate a lot form the overall access pattern of the client population. It also presents algorithms for environments where item requests by clients are dropped if not served in a certain time period. Brief comments on issues that affect performance of the discussed data broadcasting methods are also made.