Girish Welling

An architecture for adaptive QoS and its application to multimedia systems design

We describe a prototype implementation of a distributed multimedia system that generalizes the concept of QoS to all layers of its software architecture. Each layer deals with QoS at its appropriate level of abstraction using a generic API for communicating QoS parameters and values to layers above and below. The aggregation of these parameters and values is called a service contract. This architecture provides a hierarchical framework to design adaptive multimedia systems. Furthermore, the API allows for reporting of contract violations as well as dynamic renegotiation of the contract terms. A proof-of-concept multimedia system was built to evaluate the proposed architecture. Key components of this system are: a graphical user interface that dynamically requests the quality expected by the user to lower level components, a dynamic network service that efficiently matches network resources to user requirements and a processor scheduler which schedules tasks according to their execution requirements. Our experience with this system showed that the proposed architecture is an efficient framework for building adaptive multimedia systems.

An architecture for exporting environment awareness to mobile computing applications

In mobile computing, factors such as add-on hardware components and heterogeneous networks result in an environment of changing resource constraints. An application in such a constrained environment must adapt to these changes so that available resources are properly utilized. We propose an architecture for exporting awareness of the mobile computing environment to an application. In this architecture, a change in the environment is modeled as an asynchronous event that includes information related to the change. Events are typed and are organized as an extensible class hierarchy so that they can be handled at different levels of abstraction according to the requirement of each application. We also compare two approaches to structure an adaptive application. One addresses the problem of incorporating adaptiveness into legacy applications, while the other considers the design of an application with adaptiveness in mind.

A cluster-based active router architecture

The Clara prototype architecture collocates routing and computational functionality within a network, providing a scalable, high-performance computing switch router for computational services. Multiple off-the-shelf PCs provide Clara with computational power to, for example, perform real-time transcoding of video with minimal overhead.

The JOURNEY active network model

Faster processors are quickly enabling a new class of computationally intensive applications that actively transform information flows. Performing such computation at the terminal end is contrary to current trends toward low-power terminal devices. Moreover, scalability and efficiency concerns are also encouraging service providers to outsource computation when operating under loaded conditions. To address the problem of deploying such applications, we introduce the JOURNEY network model, which provides computation as an integrated network service. Contrary to other distributed computing models, JOURNEY does not attempt to guarantee that a given computational job will indeed be completed. Instead, the JOURNEY model trades off such hard guarantees in favor of architectural simplicity, and hence scalability. In order for the JOURNEY model to be applicable to real-time multimedia flows, we introduce the notion of soft quality-of-service (QoS) that provides a probabilistic bound on the unprocessed packet rate (UPR). Based on this notion, we describe a packet-processing admission control algorithm that additionally takes into consideration a flows real-time constraints. We also propose a computing router architecture that is based on cluster technology. This architecture can track technology advances in both routing and computing independently. We further present a motivating multimedia application that employs a semantically driven video transcoding service within the JOURNEY framework we implemented, and describe our experience along with performance measurements.

Session mobility support for multimedia applications

In this paper, we consider the problem of providing multimedia services to mobile clients, from the viewpoint of designing applications and systems that support session mobility. We present a software architecture for multimedia services that supports session hand-off between service providers, and allows operating parameters of all components of the session to be altered as part of the hand-off. We describe a user interface that simplifies initiating session mobility, while taking into consideration display device capability. We discuss the system support that is necessary, and describe the implementation of our ideas within our software architecture.

A user-centric view of QoS-aware communication

Recent technological advances coupled with new trends in using todays computing and communication infrastructure have raised new challenges in designing user interfaces for distributed multimedia applications. It has become essential to present the idea of QoS to the user, not only due to limitations of the infrastructure, but also because of the need to control user-machine interface bandwidth. In addition, a need for a tighter integration of communication and collaboration has become apparent. In this paper, we motivate the need for QoS support in the user-interface by considering shared virtual spaces, a unified communication paradigm for collaboration. We present a user-interface framework which provides the user with implicit and explicit control of quality of service, and describe our experience in designing and implementing such systems.

QoS Aware Browsing in Distributed Multimedia Systems

It has been widely recognized that QoS is important in designing distributed, interactive multimedia systems. However, although much has been said about QoS in the networking domain, and to a lesser degree in processor scheduling, there has hardly been any research activity concerning QoS in the user interface community. We show how the use of 3D graphics techniques in the user interface can lead to a natural way of implicitly specifying and presenting QoS to the end-user. Further, we introduce the concept of generic QoS control tools that allow users to explicitly control and monitor quality of service across different media types. In order to support such a novel user interface, a mechanism is needed to communicate these quality requirements to lower level system components. Although there exists a plethora of QoS architectures that define the semantics and interface of every component in many different ways, none offers a definitive way of structuring QoS aware systems. We instead propose a generalized, abstract concept of QoS for all layers of a software architecture. Each layer in a software system deals with QoS at its appropriate level of abstraction using a generic API for communicating QoS parameters and values to layers above and below. We call the aggregation of these parameters and values a “service contract”. This abstract concept can be applied recursively to build hierarchies of services. This paper describes our framework for building QoS aware software systems and explains in detail the user interface for a multimedia browser as an example application.