Comparing Push- and Pull-Based Broadcasting

Abstract

The first main goal of this paper is to present Sketch-it!, a framework aiming to facilitate development and experimental evaluation of new scheduling algorithms. It comprises many helpful data-structures, a graphical interface with several components and a library with implementations of selected scheduling algorithms. Every scheduling problem covered by the classification-scheme originally proposed by Graham et al. [22] can easily be integrated into the framework.

One of the more recent enhancements of this scheme, the so called broadcast scheduling problem, was chosen for an extensive case study of Sketch-it!, yielding very interesting experimental results that represent the second main contribution of this paper. In broadcast scheduling many clients listen to a high bandwidth channel on which a server can transmit documents of a given set. Over time the clients request certain documents. In the pull-based setting each client has access to a slow bandwidth channel whereon it notifies the server about its requests. In the push-based setting no such channel exists. Instead it is assumed that requests for certain documents arrive randomly with probabilities known to the server. The goal in both settings is to generate broadcast schedules for these documents which minimize the average time a client has to wait until a request is answered.

We conduct experiments with several algorithms on generated data. We distinguish scenarios for which a slow feedback channel is very advantageous, and others where its benefits are negligible, answering the question posed in the title.

Supported by the joint Berlin/Zürich graduate program CGC, financed by ETH Zürich and German Research Foundation (DFG).

Supported by DFG grant Ma 870/6-1 (SPP 1126: Algorithmics of large and complex Networks) and by DFG grant Ma 870/5-1 (Leibniz Award Ernst W. Mayr.)