We present our experience in implementing a group communication toolkit in Objective Caml, a dialect of the ML family of programming languages. We compare the toolkit both quantitatively and qualitatively to a predecessor toolkit which was implemented in C. Our experience shows that using the high-level abstraction features of ML gives substantial advantages. Some of these features, such as automatic memory management and message marshalling, allowed us to concentrate on those pieces of the implementation which required careful attention in order to achieve good performance. We conclude with a set of suggested changes to ML implementations.

Although building systems from components has attractions, this approach also has problems. Can we be sure that a certain configuration of components is correct? Can it perform as well as a monolithic system? Our paper answers these questions for the Ensemble communication architecture by showing how, with help of the Nuprl formal system, configurations may be checked against specifications, and how optimized code can be synthesized from these configurations. The performance results show that we can substantially reduce end-to-end latency in the already optimized Ensemble system. Finally, we discuss whether the techniques we used are general enough for systems other than communication systems.

Maestro is a middleware support tool for distributed multimedia and collaborative computing applications. These applications share a common need for managing multiple subgroups while providing possibly different quality-of-service guarantees for each of these groups. Maestro's functionality maps well into these requirements, and can significantly shorten the development time of such applications. In this paper, we report on Maestro, and demonstrate its utility in implementing several multimedia and collaborative computing applications. In particular, we provide a detailed description of the implementation of IMUX, a pseudo X-server (proxy) for collaborative computing applications that is based on Maestro. Copyright © 1999 John Wiley & Sons, Ltd.

There are many methods for making a multicast protocol “reliable.” At one end of the spectrum, a reliable multicast protocol might offer tomicity guarantees, such as all-or-nothing delivery, delivery ordering, and perhaps additional properties such as virtually synchronous addressing. At the other are protocols that use local repair to overcome transient packet loss in the network, offering “best effort” reliability. Yet none of this prior work has treated stability of multicast delivery as a basic reliability property, such as might be needed in an internet radio, television, or conferencing application. This article looks at reliability with a new goal: development of a multicast protocol which is reliable in a sense that can be rigorously quantified and includes throughput stability guarantees. We characterize this new protocol as a “bimodal multicast” in reference to its reliability model, which corresponds to a family of bimodal probability distributions. Here, we introduce the protocol, provide a theoretical analysis of its behavior, review experimental results, and discuss some candidate applications. These confirm that bimodal multicast is reliable, scalable, and that the protocol provides remarkably stable delivery throughput.

Trends in networking and distributed computing are creating a new generation of applications that must adapt as the environment within which they execute changes. Examples of adaptation include switching protocols to overcome a security exposure or failure mode seen only in certain settings, changing data rates to accommodate a slow link, or adapting the behavior of a high level application to match the set of participants using the application. We describe the Ensemble system, a tool for building adaptive distributed programs. © 1998 John Wiley & Sons, Ltd.

Layering of communication protocols offers many well-known advantages but typically leads to performance inefficiencies. We present a model for layering, and point out where the performance problems occur in stacks of layers using this model. We then investigate the common execution paths in these stacks and how to identify them. These paths are optimized using three techniques: optimizing the computation, compressing protocol headers, and delaying processing. All of the optimizations can be automated in a compiler with the help of minor annotations by the protocol designer. We describe the performance that we obtain after implementing the optimizations by hand on a full-scale system.

The Horus system supports a communication architecture that treats protocols as instances of an abstract data type.This approach encourages developers to partition complex protocols into simple microprotocols, each of which is implemented by a protocol layer.Protocol layers can be stacked on top of each other in a variety of ways, at run-time.First, we describe the classes of protocols that can be supported this way.Next, we present the Horus object model that we designed for this technology, and the interface between the layers that makes it all work.We then present an example layer that implements a group membership protocol.Next, we show how, given a set of required properties, an appropriate stack can be constructed.We look at an example stack of protocols, which provides fault-tolerant, totally ordered communication between a group of processes.The work contributes a standard framework for protocol development and experimentation, provides a high performance implementation of the virtual synchrony model, and introduces a methodology for increasing the robustness of the protocol development process.