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Video on Demand VOD is a multimedia service which allows a remote user to select and then view video at his convenience at any time he wants. Required bandwidth and latency time, defined as a user maximum waiting time, are usually among the most critical issues in VoD systems. Previous works in the field may be classified within two categories of protocols; namely reactive and proactive. Proactive protocols broadcast video regardless of the number of participating viewers. Reactive protocols, however, broadcast any given video upon the request by at least one client. While the former save bandwidth at high workloads, the later save bandwidth at low workloads.In this paper, we propose a rather hybrid solution, termed Slotted Stream Tapping SST broadcasting protocol, which operates as a reactive protocol at low workloads and as a proactive one at high workloads. We start with a description of our proposed protocol and then provide an exact analytical study of its keys parameters and performance measures. We show that under all different workloads, our SST protocols requires indeed less bandwidth than even the optimal Stream Tapping reactive protocol, performs much better than many well known proactive protocols and assures at high workloads a very reasonable performance with respect to the optimal proactive protocol; namely the Harmonic Broadcasting protocol, yet very easy to implement.

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Video on demand (VoD) Protocols are classified into two categories: Proactive and Reactive protocols. Proactive protocols are recommended to broadcast frequently requested (popular) movies. For less frequently requested (unpopular) videos reactive protocols performs much better in tenns of bandwidth and hence are recommended. As the request frequency changes over time, VoD service providers are not able to optimally allocation to diff erent ongoing requested movies. A hybrid broadcasting protocol that performs like reactive protocols at low workload and like proactive protocols at high workload is needed. Unfortunately, only few works have focused on this issue.In this paper we present a comparative study between previous known hydride protocols namely the Universal Broadcasting protocois (UD), the DynamiC Heuristic Broadcasting protocol (DHB) and our recent hybrid protocol Slotted Stream Tapping (SST). We show that SST outperfonns the two others at low workloads. While at high workloads, UD and DHB provide a slight bandwidth saving, SST is more practical and extremely easier to implement.

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