A Hybrid Architecture - Scalable Continuous Media Streaming Systems - page 331

19

A Hybrid Architecture

This chapter illustrates a hybrid approach to developing multicast media streaming systems.
In particular, we describe the design, analysis, and implementation of a Super-Scalar Video-
on-Demand (SS-VoD) system that integrates the techniques of batching, patching, and
periodic broadcasting. Instead of striving for maximum multicast efficiency, we focus on a
number of practical issues in designing the SS-VoD architecture, such as implementation
and deployment complexity, buffer requirement, multicast channel switching frequency,
support of interactive playback controls, etc. As well as describing the design choices,
we also devise a technique to model this relatively complex system so that approximate
performance results can be obtained without requiring lengthy simulations. Finally, we
briefly describe the implementation of the system and present some experimental results.

19.1 A Super-Scalar Architecture
Figure 19.1 depicts the overall architecture of the Super-Scalar Video-on-Demand (SS-VoD)
system. The system comprises a number of service nodes connected via a multicast-capable
network to the clients. The clients form clusters according to their geographical proximity.
An admission controller in each cluster performs authentication and schedules requests for
forwarding to the service nodes.
Each service node operates independently of the rest, having its own disk storage, memory,
CPU, and network interface. Hence a service node is effectively a mini video server, albeit
serving a small number of video titles to the entire user population. This modular architecture
can simplify the deployment and management of the system. For example, since the configu-
ration of each service node is decoupled from the scale of the system and each service node
carries just a few movies, a service provider simply deploys the right number of service nodes
according to the desired video selections. Additional service nodes can be added when more
movie selections are needed, with the existing nodes remain unchanged.
SS-VoD achieves scalability and bandwidth efficiency with two techniques. The first tech-
nique is through the use of multicast to serve multiple clients using a single multicast channel.
However, simple multicast such as those used in a near-video-on-demand (NVoD) system,