Open-Loop Algorithms - Scalable Continuous Media Streaming Systems - page 309

18

Open-Loop Algorithms

This chapter introduces open-loop multicast streaming algorithms that all have fixed media
transmission schedules irrespective of the workload of the system. This implies that the
complexity will be shifted to the clients, where the reception schedules and the playback
schedules are to be optimized to selectively receive media data from one or more of the
multicast channels to sustain continuous media playback. We first define a taxonomy and
then briefly review some of the existing open-loop algorithms. Next we present a Conso-
nant Broadcasting algorithm in detail to illustrate the design constraints and performance
trade-offs in open-loop algorithms. Finally, we present numerical and experimental results
to illustrate the characteristics, performance, and practical issues of open-loop multicast
streaming algorithms.

18.1 Introduction
Open-loop architectures, also known as periodic broadcasting, have fixed schedules for all
media streaming channels irrespective of the user arrival pattern. A new user will receive
media data from one or more of the pre-scheduled multicast channels to sustain continuous
playback. This implies that the server load is constant regardless of the number of concurrent
users in the system. Therefore as long as the network can support it, in principle, there is no
limit to how many users an open-loop multicast streaming algorithm can support.
In the past decade researchers have developed many innovative open-loop multicast
streaming algorithms. Some examples are the Pyramid Broadcasting scheme proposed by
Viswanathan and Imielinski [1], the Skyscraper Broadcasting scheme proposed by Hua and
Sheu [2], the Greedy Disk-Conserving Broadcasting scheme proposed by Gao et al. [3], the
Staircase Data Broadcasting scheme proposed by Juhn and Tseng [4], the Harmonic Broad-
casting scheme proposed by Juhn and Tseng [5], the Poly-harmonic Broadcasting scheme
proposed by Paris et al. [6], the Pagoda Broadcasting scheme proposed by Paris et al. [7], and
many others [8-11]. Interested readers are referred to the study by Hu [12] for a comprehensive
study of the existing periodic broadcasting schemes.