1926668
Exploring "Multiple Worlds" in Parallel
We examine computing alternative solutions to a problem in parallel to improve response time.Problems with exploring multiple alternatives in parallel include (1) side-effects and (2) combinatorial ...
1973175
The AURORA Gigabit Testbed
Abstract AURORA is one of five U.S. networking testbeds charged with exploring applications of, and technologies necessary for, networks operating at gigabit per second or higher bandwidths. The emphasis of the AURORA testbed, distinct from the other four testbeds, BLANCA, CASA, NECTAR and VISTANET, is research into the supporting technologies for gigabit networking. Like the other testbeds, AURORA itself is an experiment in collaboration, where government initiative (in the form of the Corporation for National Research Initiatives, which is funded by DARPA and the National Science Foundation) has spurred interaction among pre-existing centers of excellence in industry, academia, and government. AURORA has been charged with research into networking technologies that will underpin future high-speed networks. This paper provides an overview of the goals and methodologies employed in AURORA, and points to some preliminary results from our first year of research, ranging from analytic results to experimental prototype hardware. This paper enunciates our targets, which include new software architectures, network abstractions, and hardware technologies, as well as applications for our work.
18179112
Balancing performance and flexibility with hardware support for network architectures
The goals of performance and flexibility are often at odds in the design of network systems. The tension is common enough to justify an architectural solution, rather than a set of context-specific solutions. The Programmable Protocol Processing Pipeline (P4) design uses programmable hardware to selectively accelerate protocol processing functions. A set of field-programmable gate arrays (FPGAs) and an associated library of network processing modules implemented in hardware are augmented with software support for function selection and composition, and applied to processing-intensive portions of a user-programmable protocol stack. The system is sufficiently flexible to support protocol stacks that are dynamically altered in reaction to changing network conditions or user needs.The P4 can be transparently inserted into a conventional protocol architecture, such as that of TCP/IP. This experimental demonstration shows that the P4's programmability can be used to significantly improve the performance of TCP/IP under operating conditions where the protocol would perform poorly without augmentation. Generalizing from these experiments, the P4 is shown to have many applications as an open platform for implementing adaptive and programmable networks, and has illustrated new security issues that arise in FPGA-based architectures.The P4 and closely-related systems, such as network processors, are attractive architectural solutions to balancing performance and flexibility.
11110729
Active bridging
Active networks accelerate network evolution by permitting the network infrastructure to be programmable, on a per-user, per-packet, or other basis. This programmability must be balanced against the safety and security needs inherent in shared resources.This paper describes the design, implementation, and performance of a new type of network element, an Active Bridge. The active bridge can be reprogrammed "on the fly", with loadable modules called switchlets. To demonstrate the use of the active property, we incrementally extend what is initially a programmable buffered repeater with switchlets into a self-learning bridge, and then a bridge supporting spanning tree algorithms. To demonstrate the agility that active networking gives, we show how it is possible to upgrade a network from an "old" protocol to a "new" protocol on-the-fly. Moreover, we are able to take advantage of information unavailable to the implementors of either protocol to validate the new protocol and fall back to the old protocol if an error is detected. This shows that the Active Bridge can protect itself from some algorithmic failures in loadable modules.Our approach to safety and security favors static checking and prevention over dynamic checks when possible. We rely on strong type checking in the Caml language for the loadable module infrastructure, and achieve respectable performance. The prototype implementation on a Pentium-based HP Netserver LS running Linux with 100 Mbps Ethernet LANS achieves ttcp throughput of 16 Mbps between two PCs running Linux, compared with 76 Mbps unbridged. Measured frame rates are in the neighborhood of 1800 frames per second.
16792950
Task-structure analysis for knowledge modeling
n recent years there has been increasing interest in describing complicated information processing systems in terms of the knowledge they have, rather than by the details of their implementation. This requires a means of modeling the knowledge in a system. Several different approaches to knowledge modeling have been developed by researchers working in Artificial Intelligence (AI). Most of these approaches share the view that knowledge must be modeled with respect to a goal or task. In this article , we outline our modeling approach in terms of the notion of a task-structure, which recursively links a task to alternative methods and to their subtasks. Our emphasis is on the notion of modeling domain knowledge using tasks and methods as mediating concepts. We begin by tracing the development of a number of different knowledge-modeling approaches. These approaches share many features, but their differences make it difficult to compare systems that have been modeled using different approaches. We present these approaches and describe their similarities and differences. We then give a detailed description , based on the task structure, of our knowledge-modeling approach and illustrate it with task structures for diagnosis and design. Finally, we show how the task structure can be used to compare and unify the other approaches. A knowledge-based system (KBS) has explicit representations of knowledge as well as inference processes that operate on these representations to achieve a goal. An inference process consists of a number of inference steps, each step creating additional knowledge. The process of applying inference steps is repeated until the information needed to fulfill the requirements of the problem-solving goal or task is generated. Typically, both domain knowledge and possible inference steps have to be modeled and represented in some form. In one sense, knowledge is of general utility-the same piece can be utilized in different contexts and problems; so, unlike traditional procedural approaches, knowledge should not be tied to one task or goal. On the other hand, it is difficult to know what knowledge to put in a system without having an idea of the tasks the KBS will confront. In spite of claims of generality, all KBSs are designed with some task or class of tasks in mind. Similarly, they are designed to be operational across some range of domains. Thus, a clear understanding of the relationship between tasks, knowledge and inferences required to perform the task is needed before knowledge in …
16384039
Experimenting with object navigation in parallel object databases
This paper addresses the problem of selecting the best object navigation strategy for a query to be run in parallel, when considering multiple alternative strategies. This is done by performing experiments with three pointer-based join algorithms, running simple and complex queries in a parallel ODMG-compliant object database system. We believe our results provide insights into how physical properties of queries impact on the performance of different joins operators in a parallel environment.
1278902
Conceptual modeling of audio-visual content
The explosive growth of applications involving digital audio-visual material is driving the need for more rich content description. The authors present a design process for audio-visual content description. The process involves constructing a conceptual model in which entities, attributes and relationships important for content description are identified and modeled. The procedure provides special handling of different types of spatio-temporal relationships important for audio-visual content modeling. The authors describe the audio-visual content description conceptual modeling methodology in the context of the MPEG-7 description schemes.
7058627
Fast and Controllable Simulation of the Shattering of Brittle Objects
We present a method for the rapid and controllable simulation of the shattering of brittle objects under impact. An object to be broken is represented as a set of point masses connected by distance-preserving linear constraints. This use of constraints, rather than stiff springs, gains us a significant advantage in speed while still retaining fine control over the fracturing behavior. The forces exerted by these constraints during impact are computed using Lagrange multipliers. These constraint forces are then used to determine when and where the object will break, and to calculate the velocities of the newly created fragments. We present the details of our technique together with examples illustrating its use.
7544123
Models and Heuristics for Robust Resource Allocation in Parallel and Distributed Computing Systems
This is an overview of the robust resource allocation research efforts that have been and continue to be conducted by the CSU robustness in computer systems group. Parallel and distributed computing systems, consisting of a (usually heterogeneous) set of machines and networks, frequently operate in environments where delivered performance degrades due to unpredictable circumstances. Such unpredictability can be the result of sudden machine failures, increases in system load, or errors caused by inaccurate initial estimation. The research into developing models and heuristics for parallel and distributed computing systems that create robust resource allocations is presented.