Person:

Schwan, Karsten

Permanent Link

https://hdl.handle.net/1853/71682

Associated Organization(s)

Organizational Unit

College of Computing

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Publication Search Results

Now showing 1 - 10 of 46

Experimentation with Event-Based Methods of Adaptive Quality of Service Management

(Georgia Institute of Technology, 1999) West, Richard ; Schwan, Karsten

Many complex distributed applications require quality of service (QoS) guarantees on the end-to-end transfer of information across a distributed system. A major problem faced by any system, or infrastructure, providing QoS guarantees to such applications is that resource requirements and availability may change at run-time. Consequently, adaptive resource (and, hence, service) management mechanisms are required to guarantee quality of service to these applications. This paper describes different methods of adaptive quality of service management, implemented with the event-based mechanisms offered by the Dionisys quality of service infrastructure. Dionisys allows applications to influence: (1) how service should be adapted to maintain required quality, (2) when such adaptations should occur, and (3) where these adaptations should be performed. In Dionisys, service managers execute application-specific functions to monitor and adapt service (and, hence, resource usage and allocation), in order to meet the quality of service requirements of adaptable applications. This approach allows service managers to provide service in a manner specific to the needs of individual applications. Moreover, applications can monitor and pin-point resource bottlenecks, adapt their requirements for heavily-demanded resources, or adapt to different requirements of alternative resources, in order to improve or maintain their overall quality of service. Likewise, service managers can cooperate with other service managers and, by using knowledge of application-specific resource requirements and adaptation capabilities, each service manager can make better decisions about resource allocation. Using a real-time client-server application, built on top of Dionisys, we compare alternative strategies for adapting and coordinating CPU and network services. In this fashion, we demonstrate the importance of flexibility in quality of service management.
AASERT : dynamic configuration of distributed objects : on-line monitoring

(Georgia Institute of Technology, 1999) Schwan, Karsten
Real-Time Visualization in Distributed Computational Laboratories

(Georgia Institute of Technology, 1999) King, Davis ; Schwan, Karsten ; Eisenhauer, Greg S. ; Plale, Beth ; Isert, Carsten

Large data volumes cannot be transported, processed or displayed in real-time unless we apply to them general or application-specific compression and filtering techniques. In addition, when multiple end users inspect such data sets or when multiple programs access or consume them, data distribution and display should be performed differentially, in accordance with the queries generated by programs or end users. Finally, if dynamic access queries cannot be formulated precisely, then they must be refined as they progress in order to avoid unnecessary data retrievals, transfers, and information overload for programs or end users with uninteresting or unimportant data. The principal idea of our research is to create Active User Interfaces (AUIs) that continuously emit events describing their internal states and/or current information needs. Based on these events, we then develop methods for controlling the information streams directed at these interfaces, for single and for multiple, collaborating end users. The purposes of stream control are twofold. First, stream control is performed to deal with heterogeneous underlying hardware and software systems, where streams may originate at secondary storage media or may be generated dynamically, may have to be moved across the Internet or may utilize local area or high performance interconnects, and where collaborating user interfaces may range from low end PC-based displays to high end immersive visualization engines. Second, stream control aims to achieve scalability for user interfaces to large-scale, complex data streams directed at them, by offloading computations from visualizations to information generators or to information routing sites, to dynamically migrate such computations to appropriate locations, and to adapt these computations in order to effect tradeoffs in the amount of data moved across network links vs. the computations required when performing data rendering, compression, filtering, and routing actions.
Min-cut Methods for Mapping Dataflow Graphs

(Georgia Institute of Technology, 1999) Elling, Volker Wilhelm ; Schwan, Karsten

High performance applications and the underlying hardware platforms are becoming increasingly dynamic; runtime changes in the behavior of both are likely to result in inappropriate mappings of tasks to parallel machines during application execution. This fact is prompting new research on mapping and scheduling the dataflow graphs that represent parallel applications. In contrast to recent research which focuses on critical paths in dataflow graphs, this paper presents new mapping methods that compute near-min-cut partitions of the dataflow graph. Our methods deliver mappings that are an order of magnitude more efficient than those of DSC, a state-of-the-art critical-path algorithm, for sample high performance applications.
Scalable Scheduling Support for Loss and Delay Constrained Media Streams

(Georgia Institute of Technology, 1998) West, Richard ; Schwan, Karsten ; Poellabauer, Christian

Real-time media servers need to service hundreds and, possibly, thousands of clients, each with their own quality of service (QoS) requirements. To guarantee such diverse QoS requires fast and efficient scheduling support at the server. This paper describes the practical issues concerned with the implementation of a scalable real-time packet scheduler resident on a server, designed to meet service constraints on information transferred across a network to many clients. Specifically, we describe the implementation issues and performance achieved by Dynamic Window-Constrained Scheduling (DWCS), which is designed to meet the delay and loss constraints on packets from multiple streams with different performance objectives. In fact, DWCS is designed to limit the number of late packets over finite numbers of consecutive packets in loss-tolerant and/or delay-constrained, heterogeneous traffic streams. We show how DWCS can be efficiently implemented to provide service guarantees to hundreds of streams. We compare the costs of different implementations, including an approximation algorithm, which trades service quality for speed of execution.
Interactors: Capturing Tradeoffs in Bandwidth Versus CPU Usage for Quality of Service Constrained Objects

(Georgia Institute of Technology, 1998) West, Richard ; Schwan, Karsten

Complex distributed applications, including virtual environments, and real-time multimedia require performance guarantees in the end-to-end transfer of information across a network. To make such guarantees requires the management of processing, memory, and network resources. This paper describes the Dionisys end-system quality of service (QoS) approach to specifying, translating, and enforcing end-to-end, object-level QoS constraints. Dionisys differs from previous work on QoS architectures by supporting QoS constraints on distributed shared objects, as well as multimedia streams. Consequently, we introduce 'interactors', which capture the QoS constraints and resource requirements at each stage in the generation, processing, and transfer of information between multiple cooperating objects. Using interactors, Dionisys is able to coordinate both thread and packet-level scheduling, so that information is processed and transmitted at matching rates. However, there are tradeoffs in the use of CPU cycles for scheduling and the need to meet QoS constraints on the information transferred between interacting objects. We show, empirically, the packet scheduling frequency to minimize CPU overheads while maximizing bandwidth usage.
IR-DOMS project (SBIR)

(Georgia Institute of Technology, 1998) Schwan, Karsten
Adaptation and Specialization for High Performance Mobile Agents

(Georgia Institute of Technology, 1998) Zhou, Dong ; Schwan, Karsten

Mobile agents as a new design paradigm for distributed computing potentially permit network applications to operate across dynamic and heterogeneous systems and networks. Agent computing, however, is subject to inefficiencies due to the complexities of the environments in which agents are deployed, which requires agent-based programs to rely on underlying agent systems to mask some of those complexities, by using system-wide, uniform representations of agent code and data and by 'hiding' the volatility in agents' 'spatial' relationships. This paper explores two approaches for improving the performance of agent-based programs: (1) runtime adaptation and (2) agent specialization. Our general aim is to enable programmers to employ these techniques to improve program performance without sacrificing the fundamental advantages promised by mobile agent programming. The specific results in this paper demonstrate the beneficial effects of agent adaptation both for a single mobile agent and for several cooperating agents, using the adaptation techniques of agent morphing and agent fusion. Experimental results are attained with two sample high performance distributed applications, derived from the scientific domain and from sensor-based codes, respectively.
IR-DOMS project (SBIR) : phase II

(Georgia Institute of Technology, 1998) Schwan, Karsten
Dynamic Window-Constrained Scheduling for Multimedia Applications

(Georgia Institute of Technology, 1998) West, Richard ; Schwan, Karsten

Advances in network technologies have introduced opportunities for applications such as video conferencing, tele-medicine, and real-time multimedia applications. These applications require strict performance (or quality of service) requirements on the information transferred across a network. This paper describes a new algorithm, called Dynamic Window-Constrained Scheduling (DWCS), designed to meet the service constraints on packets from multiple streams with different performance objectives. Using only two attributes, a deadline and a loss-tolerance per packet stream, we show DWCS: (1) can limit the number of late packets over finite numbers of consecutive packets in loss-tolerant or delay-constrained, heterogeneous traffic streams, (2) does not require a-priori knowledge of the worst-case loading from multiple streams to establish the necessary bandwidth allocations to meet per-stream delay and loss-constraints, (3) can safely drop late packets in lossy streams without unnecessarily transmitting them, thereby avoiding unnecessary bandwidth consumption, and (4) can exhibit both fairness and unfairness properties when necessary. In fact, DWCS can perform fair-bandwidth allocation, static priority (SP) and earliest-deadline first (EDF) scheduling. We show the effectiveness of DWCS using a streaming video application, running over ATM.