Beckman Institute            University of Illinois at Urbana-Champaign             

Documentation Table of Contents

The first release of Syzygy on the web was in September 2000. Our initial goal was to run a wide range of VR applications on a PC cluster with equal performance to shared-memory SMP computers like the SGI Onyx, the preferred platform for high-end VR. We have since worked to make the system portable, robust, and easy to use. We have also tried to make the Syzygy application model better suited to a variety of environments, including single PCs and laptops, wide-area networked systems, and even the older shared-memory SMP systems.

Changes in hardware platform drive software changes. In this case, PC cluster application development requires explicit library support and an updated application model. Monolithic shared memory systems allow library writers to ignore a whole range of data sharing issues, leaving these to the applications programmer and encouraging him to write non-portable code.

Consider the requirements for PC cluster software in more detail. Communications between processors consitutes a bottleneck. Tools are needed to efficiently manage and develop cluster applications. The developer needs an API that supports complex communications between cluster machines. These information exchanges must be fault-tolerant and conducted in a way that keeps the cluster producing frame-by-frame synchronized views of the virtual world. During the early stages of application development, the application code may be unstable, so the overall distributed system must tolerate the failure of individual components. The system needs the ability to portably launch applications across a wide range of target clusters, both homogeneous and heterogenous in nature. It also needs mechanisms for steering running applications and monitoring tools that allow users to remotely determine its state.

The goal of creating VR applications on a PC cluster is best served by increasing the level of abstraction and writing a toolkit with broader applicability. Syzygy aims to provide simple software tools for building heterogeneous distributed systems. While the system's main focus is PC clusters on high performance LANs, it is also applicable to WAN-based systems. Syzygy is designed to be a lightweight toolkit that can operate on PC clusters, SMP boxes, and laptops, while connecting meaningfully with smaller devices. This presents several challenges. Much system infrastructure is unnecessary for a standalone laptop being used to provide a portable road demo, and, to maintain ease of use, the sytem's operation should scale down gracefully. Furthermore, we need to deploy communication methods suitable for SMP, namely shared memory instead of sockets, and do this while reusing our low-level communications infrastructure. Finally, performance is very important, as many of the toolkit's functions are OS-level and must be efficient.

Syzygy solves several problems: distributed graphics, distributed sound, distributed systems management, distributed data access, and general I/O device management. There are systems out there that do each of these things, but no one system addresses them all. However, each problem relies on a similar infrastructure for its solution. Syzygy aims to identify that common infrastructure and provide an implementation. Thus, each problem can be solved more easily, and the resulting code base is well-integrated, maintainable, and smaller. In effect, Syzygy is a middleware solution for distributed multimedia.

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