Scalable multimedia/video servers

The objective of scalable multimedia/video servers is to support general real-time data streaming for a variety of application types over a wide range of networks. The multimedia server complex is a set of components designed to work together and responsible for storing, managing, and concurrently delivering the multimedia contents to the applications. Such a complex has been prototyped and demonstrated, and elements are being incorporated into IBM's product line.

Depending on the size and other properties of the application(s) being supported (such as availability requirements), one or more of the elements shown in the diagram appear in the server complex. In the simplest case, all needed components can reside on a single RS/6000 system. Systems with a high availability requirement or which service a large number of streams (with a corresponding scalability requirement) may have a multiplicity of the components shown, distributed over separate hardware elements. This is illustrated more fully on the page, Scalable multimedia server complex, and its links. Below, we provide a summary view of the different components.

The applications are implemented in separate application servers distinct from the server complex. Examples of applications under consideration are

• web servers for delivering video and audio data over the internet,
• education and training,
• digital video broadcast studio (DVB),
• tailored real-time news distribution
• news-on-demand,
• residential interactive television (ITV),

Of the elements that make up the Multimedia Server Complex proper, they can be looked at as those which make up a more general purpose supporting infrastructure, useful in other server environments as well as this one; and those which are more apropos of the multimedia video server environment.

In this latter case, there are two elements. The control server manages the storage and real-time retrieval of multimedia files, balancing load between data servers in a complex, creating caching opportunities through affinity routing, and performing other optimizations to improve the responsiveness and the economics of a video server complex. The data exporter moves multimedia in continuous streams from the multimedia file system into a broadband network. As prototyped, this component has a modular design to support a variety of network types. The prototype currently supports T1 lines, digital cable television, and TCP/IP.

Elements which constitute the more general supporting infrastructure, and which might indeed be shared with other server prototypes, are threefold:

• The Calypso File System is a cluster-optimized distributed file system which provides the higher-level directory servicing (locating the data streams by user) for the server complex. Through parallelism, this POSIX-compliant system enables the scalability for stream access by the application(s), and need not be present in simpler configurations where such scalability (or availability) is not a consideration.

• The Tiger Shark File System is a parallel file system designed to support interactive multimedia systems by striping data across storage nodes and disks, permitting scheduled, cache-coherent access from one or more file system nodes to a shared pool of disks attached to one or more storage nodes. This provides scalability at the data access/management side of the complex.

• The real-time virtual shared disk (RT-VSD) component supplies the underlying capability for managing data at the disk level. It provides the shared disk image across the cluster, and does the actual retrieval of the data blocks by deadline sequence. It also need not be present in simpler configurations, in this case where disk sharing is not employed.

Together, these components from both sets have been demonstrated to be an effective, scalable solution to delivering from small numbers to thousands of concurrent multimedia streams to applications of today, and of tomorrow.