Geoffrey Coulson

An architecture for next generation middleware

This paper proposes an approach to the design of configurable and open middleware platforms based on the concept of reflection. More specifically, the paper introduces a language-independent reflective architecture featuring a per-object meta-space, the use of meta-models to structure meta-space, and a consistent use of object graphs for composite components. This is complemented by a component framework supporting the construction of meta-spaces. The paper also reports on experiences of implementing the architecture (with emphasis on experiments with open bindings).

A generic component model for building systems software

Component-based software structuring principles are now commonplace at the application level; but componentization is far less established when it comes to building low-level systems software. Although there have been pioneering efforts in applying componentization to systems-building, these efforts have tended to target specific application domains (e.g., embedded systems, operating systems, communications systems, programmable networking environments, or middleware platforms). They also tend to be targeted at specific deployment environments (e.g., standard personal computer (PC) environments, network processors, or microcontrollers). The disadvantage of this narrow targeting is that it fails to maximize the genericity and abstraction potential of the component approach. In this article, we argue for the benefits and feasibility of a generic yet tailorable approach to component-based systems-building that offers a uniform programming model that is applicable in a wide range of systems-oriented target domains and deployment environments. The component model, called OpenCom, is supported by a reflective runtime architecture that is itself built from components. After describing OpenCom and evaluating its performance and overhead characteristics, we present and evaluate two case studies of systems we have built using OpenCom technology, thus illustrating its benefits and its general applicability.

The design of a QoS-controlled ATM-based communications system in Chorus

We describe the design of an application platform able to run distributed real-time and multimedia applications alongside conventional UNIX programs. The platform is embedded in a microkernel/PC environment and supported by an ATM-based, QoS-driven communications stack. In particular, we focus on resource-management aspects of the design and deal with CPU scheduling, network resource-management and memory-management issues. An architecture is presented that guarantees QoS levels of both communications and processing with varying degrees of commitment as specified by user-level QoS parameters. The architecture uses admission tests to determine whether or not new activities can be accepted and includes modules to translate user-level QoS parameters into representations usable by the scheduling, network, and memory-management subsystems. >

Lorien: a pure dynamic component-based operating system for wireless sensor networks

In this paper we examine the current state of the art in WSN operating systems in terms of their general programming models and runtime reprogramming features. While all OSs admit the need -- and provide some capability -- for runtime reprogramming, we find that no existing OS employs a unified approach at the dynamic end of the spectrum. In this paper we present such a unified solution with a new OS design called Lorien. Lorien is a dynamic component-oriented OS aimed at permitting component-based changes to itself, including architectural change, throughout every aspect of the system at runtime including its kernel. A Lorien system typically permits 43KB -- 90% -- of program memory on the TelosB platform to be fully reprogrammable within a unified programming model, supporting rich future middleware and systems research in the WSN field.

From Requirements to Services: Group Communication Support for Distributed Multimedia Systems

The GCommS (Group Communication Support for Distributed Communication Systems) project at Lancaster University is concerned with the support of group communication, especially for applications employing multimedia information. In this paper we introduce a study on requirements of multimedia group applications. Group support in existing systems is discussed. Examples to illustrate group application requirements are given and a set of characteristics to define these requirements is introduced. Based on the requirements study application level services are proposed.

The role of reflection in supporting dynamic QoS management functions

In previous papers, the authors have reported on the design and implementation of reflective middleware platforms. The aim of this paper is to consider the implications of such an architecture for the area of quality of service (QoS) management. More specifically, the paper describes how critical QoS management functions can be incorporated into our reflective middleware platform, with particular emphasis on the dynamic QoS management functions of QoS monitoring and adaptation. It is argued that the reflective approach leads to a natural and highly flexible implementation of such QoS management functions (and indeed the approach offers considerable benefits over more conventional approaches).

Software architecture for adaptive distributed multimedia systems

To support multimedia applications in mobile environments, it will be necessary for applications to be aware of the underlying network conditions and also to be able to adapt their behaviour and that of the underlying platform. This paper focuses on the role of middleware in supporting such adaptation. In particular, we investigate the role of open implementation and reflection in the design of middleware platforms such as CORBA. The paper initially extends CORBA with the concept of explicit binding, where path of communication between objects is represented as first class objects. We then introduce the concept of open bindings which support inspection and adaptation of the path of communications. An implementation of open bindings for adaptive continuous-media interaction is described using the example of adaptive video-on-demand for mobile environments.

Intelligent dependability services for overlay networks

Application-level overlays have emerged as a useful means of offering network services that are not supported by the underlying physical network. Most overlays employ proprietary dependability mechanisms to render them more resilient to node failure; but the use of proprietary approaches leads to duplication of effort during development and adds design complexity. In this paper we propose generic dependability services which simplify the design of overlays. Our services are fully decentralized and are configurable to take advantage of current network conditions, which can enable us to make better repairs following failures.

A Model for Active Object Coordination and for Distributed Multimedia Applications

The coordination among a set of concurrent objects is commonly expressed through language specific synchronization mechanisms in the objects implementation. Unfortunately, such an approach makes it difficult to reuse these objects in applications with different coordination patterns. Moreover, the algorithms used for object coordination are inextricably linked to the original object implementation and cannot themselves be easily reused for the coordination of objects with different implementations. In this paper, we propose a model that promotes the reuse of both objects and coordination patterns. The model allows objects to synchronize their execution with events occurring in other objects (e.g. state changes and method invocations) in a way that is compatible with local object synchronization constraints and respects encapsulation. The model also supports the use of class inheritance while avoiding most of the problems of combining inheritance with synchronization. Finally, we consider the use of the model in the area of distributed multimedia applications. In this area active objects encapsulate media processing activities while a synchronous language is used to specify their temporal coordination.

Improving RSVP for better support of Internet multimedia communications

We have observed the failure of RSVP to be widely accepted as the solution to resource reservation in the Internet. Because we are convinced of the need for resource reservation, in at least parts of the Internet, to support multimedia communications, we have set about trying to improve RSVP. By careful study of the protocol, we have identified areas for improvement, and propose REDO RSVP, a reduced overhead version that includes a fast establishment mechanism (FEM). We describe the rationale for REDO RSVP and present an analysis of its features and operations.