Joseph P. Loyall

QuO's runtime support for quality of service in distributed objects

Most distributed applications are brittle; they work in a limited environment and cannot adapt to changes in this environment. Making these applications less brittle is a complex engineering task that is hard for specific application areas and even harder to generalize. The Quality Objects (QuO) project offers a framework for creating applications that adapt to different Quality of Services (QoS) offered by the underlying resources. QuO offers several layers of tools for creating adaptive distributed applications using the familiar CORBA development process of code generators and runtime support libraries. In this paper we describe the QuO Runtime and the components it uses to maintain and adapt to QoS. The QuO Runtime is the base functionality on which QuO code generators specialize for a specific adaptive application. The QuO Runtime handles much of the complexity of collecting, organizing, and acting on changing QoS, thus reducing the burden for application developers.

QoS Aspect Languages and Their Runtime Integration

Distributed object middleware, such as CORBA, hides system-and network-specific characteristics of objects behind functional interface specifications. This simplifies development and maintenance of distributed objects, contributing to their growing acceptance. Critical applications have Quality of Service (QoS) requirements, however, such as real-time performance, dependability, or security, that are hidden by middleware. Because of this, application developers often bypass distributed object systems, thus gaining little or no advantage from the middleware. We have developed Quality Objects (QuO), a framework for developing distributed applications with QoS requirements. QuO provides a set of aspect languages, called Quality Description Languages (QDL), for specifying possible QoS states, the system resources and mechanisms for measuring and controlling QoS, and behavior for adapting to changing levels of available QoS at runtime. This paper describes QuOs aspect languages, their usage, and how they interact with the QuO runtime system to form the QuO framework.

Flexible and adaptive QoS control for distributed real-time and embedded middleware

Computing systems are increasingly distributed, real-time, and embedded (DRE) and must operate under highly unpredictable and changeable conditions. To provide predictable mission-critical quality of service (QoS) end-to-end, QoS-enabled middleware services and mechanisms have begun to emerge. However, the current generation of commercial-off-the-shelf middleware lacks adequate support for applications with stringent QoS requirements in changing, dynamic environments. This paper provides two contributions to the study of adaptive middleware to control DRE applications. It first describes how priority- and reservation-based OS and network QoS management mechanisms can be coupled with standards-based, off-the-shelf distributed object computing (DOC) middleware to better support dynamic DRE applications with stringent end-to-end real-time requirements. It then presents the results of experimentation and validation activities we conducted to evaluate these combined OS, network, and middleware capabilities. Our work integrates currently missing low-level resource control capabilities for end-to-end flows with existing capabilities in adaptive DRE middleware and sets the stage for further advances in fine-grained precision management of aggregate flows using dynamic adaptation techniques.

Component-Based Dynamic QoS Adaptations in Distributed Real-Time and Embedded Systems

Large scale distributed real time and embedded (DRE) applications are complex entities that are often composed of different subsystems and have stringent Quality of Service (QoS) requirements. These subsystems are often developed separately by different developers increasingly using commercial off-the shelf (COTS) middleware. Subsequently, these subsystems need to be integrated, configured to communicate with each other, and distributed. However, there is currently no standard way of supporting these requirements in existing COTS middleware. While recently emerging component-based middleware provides standardized support for packaging, assembling, and deploying, there is no standard way to provision QoS required by the DRE applications. We have previously introduced a QoS encapsulation model, qoskets, as part of our QuO middleware framework that can dynamically adapt to resource constraints. In this paper we introduce implementing these QoS behaviors as components that can be assembled with other application components. The task of ensuring QoS then becomes an assembly issue. To do so we have componentized our QuO technology instead of integrating QuO into the middleware as a service. To date, we have demonstrated our approach of QoS provisioning in MICO, CIAO, and Boeing’s Prism component middleware. We present experimental results to evaluate the overhead incurred by these QoS provisioning components in the context of CIAO CCM. We use a simulated Unmanned Aerial Vehicle (UAV) application as an illustrative DRE application for the demonstration of QoS adaptations using qosket components.

Building adaptive distributed applications with middleware and aspects

Middleware technologies allow the development of distributed applications without explicit knowledge of the networking involved. However, in the face of changing network and CPU conditions across the distributed system, these applications often will need to adapt their behavior to maintain an acceptable quality of service (QoS), which implies a knowledge of these conditions. This adaptation is neither part of the application logic nor part of the distribution middleware, and so represents a separate concern which needs to be addressed.This paper describes an aspect-based approach to programming QoS adaptive applications that separates the QoS and adaptation concerns from the functional and distribution concerns. To simplify aspect development for these applications, our approach integrates a domain-specific adaptation specification with a novel aspect language which includes distribution and adaptation-specific join points in its join point model. We compare and contrast this with existing aspect-oriented language approaches and illustrate our approach with an example distributed system application.

Using QDL to specify QoS aware distributed (QuO) application configuration

Recent work in opening up distributed object systems to make them suitable for applications needing quality of service control has had the side effect of increasing the complexity in setting up, configuring, and initializing such applications. Configuration of distributed applications is more complicated than that of non-distributed applications, simply because of the heterogeneous and distributed nature of the applications components. CORBA and other distributed object middleware simplifies the configuration of distributed object applications, but hides much of the information and control necessary to achieve quality of service (QoS). We describe the techniques and tools that we have developed within our Quality Objects (QuO) framework for simplifying the configuration of distributed applications with QoS attributes. We describe a QuO configuration language, as well as the specific configuration needs of particular QoS properties-real-time, security, and dependability-and the support we provide for them.

An End-to-End Workflow for Engineering of Biological Networks from High-Level Specifications

We present a workflow for the design and production of biological networks from high-level program specifications. The workflow is based on a sequence of intermediate models that incrementally translate high-level specifications into DNA samples that implement them. We identify algorithms for translating between adjacent models and implement them as a set of software tools, organized into a four-stage toolchain: Specification, Compilation, Part Assignment, and Assembly. The specification stage begins with a Boolean logic computation specified in the Proto programming language. The compilation stage uses a library of network motifs and cellular platforms, also specified in Proto, to transform the program into an optimized Abstract Genetic Regulatory Network (AGRN) that implements the programmed behavior. The part assignment stage assigns DNA parts to the AGRN, drawing the parts from a database for the target cellular platform, to create a DNA sequence implementing the AGRN. Finally, the assembly stage computes an optimized assembly plan to create the DNA sequence from available part samples, yielding a protocol for producing a sample of engineered plasmids with robotics assistance. Our workflow is the first to automate the production of biological networks from a high-level program specification. Furthermore, the workflows modular design allows the same program to be realized on different cellular platforms simply by swapping workflow configurations. We validated our workflow by specifying a small-molecule sensor-reporter program and verifying the resulting plasmids in both HEK 293 mammalian cells and in E. coli bacterial cells.

Total quality of service provisioning in middleware and applications

Abstract Commercial off-the-shelf (COTS) middleware, such as real-time CORBA, is gaining acceptance in the distributed real-time and embedded (DRE) community. Existing COTS specifications, however, do not effectively separate quality of service (QoS) policy configurations and adaptations from application functionality. DRE application developers therefore often intersperse code that provisions resources for QoS guarantees and program adaptation mechanisms throughout DRE applications, making it hard to configure, validate, modify, and evolve complex DRE applications. This paper illustrates how (1) standard component-based middleware can be enhanced to flexibly compose static QoS provisioning policies with application logic, (2) adaptive middleware capabilities enable developers to abstract and encapsulate reusable dynamic QoS provisioning and adaptive behaviors, and (3) component-based middleware and adaptive middleware capabilities can be integrated to provide a total QoS provisioning solution for DRE applications.

Comparing and contrasting adaptive middleware support in wide-area and embedded distributed object applications

The Quality Objects (QuO) middleware is a set of extensions to standard distributed object computing middleware that is used to control and adapt the quality of service in a number of distributed application environments, from wide-area to embedded distributed applications. This paper compares and contrasts the characteristics of key use cases and the variations in QuO implementations that have emerged to support them. We present these variations in the context of several actual applications being developed using the QuO middleware.

A distributed real-time embedded application for surveillance, detection, and tracking of time critical targets

As computer systems become increasingly internetworked, there is a growing class of distributed realtime embedded (DRE) applications that have characteristics and present challenges beyond those of traditional embedded systems. They involve many heterogeneous nodes and links, shared and constrained resources, and are deployed in dynamic environments with changing participants. In this paper, we present a representative DRE application of medium scale that we are developing for the DARPA PCES program. This application consists of several unmanned aerial vehicles, command and control centers, and ground based combat vehicles to perform surveillance, detection, and tracking of time critical targets, an ever increasing threat in todays world. We describe the application, the scenario in which the application is being demonstrated, and issues and challenges associated with developing a DRE application of this complexity.