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Articles 931 - 960 of 1102
Full-Text Articles in Computer Sciences
A Queuing Analysis Of Bandwidth Allocation Schemes For Compressed Video, Saurab Nog, Carl J. Beckmann
A Queuing Analysis Of Bandwidth Allocation Schemes For Compressed Video, Saurab Nog, Carl J. Beckmann
Computer Science Technical Reports
Video and audio compression techniques allow continuous media streams to be transmitted at bit rates that are a function of the delivered quality of service. Digital networks will be increasingly used for the transmission of such continuous media streams. This paper describes an admission control policy in which the quality of service is negotiated at stream initiation, and is a function of both the desired quality of service and the available bandwidth resources. The advantage of this approach is the ability to robustly service large numbers of users, while providing increased quality of service during low usage periods. Several simple …
The Expected Lifetime Of "Single-Address-Space" Operating Systems, David Kotz, Preston Crow
The Expected Lifetime Of "Single-Address-Space" Operating Systems, David Kotz, Preston Crow
Computer Science Technical Reports
Trends toward shared-memory programming paradigms, large (64-bit) address spaces, and memory-mapped files have led some to propose the use of a single virtual-address space, shared by all processes and processors. Typical proposals require the single address space to contain all process-private data, shared data, and stored files. To simplify management of an address space where stale pointers make it difficult to re-use addresses, some have claimed that a 64-bit address space is sufficiently large that there is no need to ever re-use addresses. Unfortunately, there has been no data to either support or refute these claims, or to aid in …
An Rpc Mechanism For Transportable Agents, Saurab Nog, Sumit Chawla, David Kotz
An Rpc Mechanism For Transportable Agents, Saurab Nog, Sumit Chawla, David Kotz
Computer Science Technical Reports
Transportable agents are autonomous programs that migrate from machine to machine, performing complex processing at each step to satisfy client requests. As part of their duties agents often need to communicate with other agents. We propose to use remote procedure call (RPC) along with a flexible interface definition language (IDL), to add structure to inter-agent communication. The real power of our Agent RPC comes from a client-server binding mechanism based on flexible IDL matching and from support for multiple simultaneous bindings. Our agents are programmed in Agent Tcl; we describe how the Tcl implementation made RPC particularly easy to implement. …
Flexibility And Performance Of Parallel File Systems, David Kotz, Nils Nieuwejaar
Flexibility And Performance Of Parallel File Systems, David Kotz, Nils Nieuwejaar
Dartmouth Scholarship
Many scientific applications for high-performance multiprocessors have tremendous I/O requirements. As a result, the I/O system is often the limiting factor of application performance. Several new parallel file systems have been developed in recent years, each promising better performance for some class of parallel applications. As we gain experience with parallel computing, and parallel file systems in particular, it becomes increasingly clear that a single solution does not suit all applications. For example, it appears to be impossible to find a single appropriate interface, caching policy, file structure, or disk management strategy. Furthermore, the proliferation of file-system interfaces and abstractions …
Fast Compression Of Transportable Tcl Scripts, Robert S. Gray
Fast Compression Of Transportable Tcl Scripts, Robert S. Gray
Computer Science Technical Reports
An information agent is charged with the task of searching a collection of electronic resources for information that is relevant to the user's current needs. These resources are often distributed across a network and can contain tremendous quantities of data. One of the paradigms that has been suggested for allowing efficient access to such resources is transportable agents -- the agent is sent to the machine that maintains the information resource; the agent executes on this remote machine and then returns its results to the local machine. We have implemented a transportable agent system that uses the Tool Command Language …
A Performance Comparison Of Tcp/Ip And Mpi On Fddi, Fast Ethernet, And Ethernet, Saurab Nog, David Kotz
A Performance Comparison Of Tcp/Ip And Mpi On Fddi, Fast Ethernet, And Ethernet, Saurab Nog, David Kotz
Computer Science Technical Reports
Communication is a very important factor affecting distributed applications. Getting a close handle on network performance (both bandwidth and latency) is thus crucial to understanding overall application performance. We benchmarked some of the metrics of network performance using two sets of experiments, namely roundtrip and datahose. The tests were designed to measure a combination of network latency, bandwidth, and contention. We repeated the tests for two protocols (TCP/IP and MPI) and three networks (100 Mbit FDDI (Fiber Distributed Data Interface), 100 Mbit Fast Ethernet, and 10 Mbit Ethernet). The performance results provided interesting insights into the behaviour of these networks …
Transportable Information Agents, Robert Gray, Daniela Rus, David Kotz
Transportable Information Agents, Robert Gray, Daniela Rus, David Kotz
Computer Science Technical Reports
We have designed and implemented autonomous software agents. Autonomous software agents navigate independently through a heterogeneous network. They are capable of sensing the network configuration, monitoring software conditions, and interacting with other agents. Autonomous agents are implemented as transportable programs, e.g., programs that are capable of suspending execution, moving to a different machine, and starting from where they left off. We illustrate the intelligent behavior of autonomous agents in the context of distributed information-gathering tasks.
Compositional Reasoning Is Not Possible In Determining The Solvability Of Consensus, Prasad Jayanti
Compositional Reasoning Is Not Possible In Determining The Solvability Of Consensus, Prasad Jayanti
Computer Science Technical Reports
Consensus, which requires processes with different input values to eventually agree on one of these values, is a fundamental problem in fault-tolerant computing. We study this problem in the context of asynchronous shared-memory systems. In our model, shared-memory consists of a sequence of cells and supports a specific set of operations. Prior research on consensus focussed on its solvability in shared-memories supporting specific operations. In this paper, we investigate the following general question: Let OP1 and OP2 be any two sets of operations such that each set includes read and write operations. Suppose there is no consensus protocol for N …
Introduction To Multiprocessor I/O Architecture, David Kotz
Introduction To Multiprocessor I/O Architecture, David Kotz
Dartmouth Scholarship
The computational performance of multiprocessors continues to improve by leaps and bounds, fueled in part by rapid improvements in processor and interconnection technology. I/O performance thus becomes ever more critical, to avoid becoming the bottleneck of system performance. In this paper we provide an introduction to I/O architectural issues in multiprocessors, with a focus on disk subsystems. While we discuss examples from actual architectures and provide pointers to interesting research in the literature, we do not attempt to provide a comprehensive survey. We concentrate on a study of the architectural design issues, and the effects of different design alternatives.
A 2-2/3 Approximation For The Shortest Superstring Problem, Chris Armen, Clifford Stein
A 2-2/3 Approximation For The Shortest Superstring Problem, Chris Armen, Clifford Stein
Computer Science Technical Reports
Given a collection of strings S={s_1, ..., s_n} over an alphabet \Sigma, a superstring \alpha of S is a string containing each s_i as a substring; that is, for each i, 1<=i<=n, \alpha contains a block of |s_i| consecutive characters that match s_i exactly. The shortest superstring problem is the problem of finding a superstring \alpha of minimum length. The shortest superstring problem has applications in both data compression and computational biology. In data compression, the problem is a part of a general model of string compression proposed by Gallant, Maier and Storer (JCSS '80). Much of the recent interest in the problem is due to its application to DNA sequence assembly. The problem has been shown to be NP-hard; in fact, it was shown by Blum et al.(JACM '94) to be MAX SNP-hard. The first O(1)-approximation was also due to Blum et al., who gave an algorithm that always returns a superstring no more than 3 times the length of an optimal solution. Several researchers have published results that improve on the approximation ratio; of these, the best previous result is our algorithm ShortString, which achieves a 2 3/4-approximation (WADS '95). We present our new algorithm, G-ShortString, which achieves a ratio of 2 2/3. It generalizes the ShortString algorithm, but the analysis differs substantially from that of ShortString. Our previous work identified classes of strings that have a nested periodic structure, and which must be present in the worst case for our algorithms. We introduced machinery to descibe these strings and proved strong structural properties about them. In this paper we extend this study to strings that exhibit a more relaxed form of the same structure, and we use this understanding to obtain our improved result.
Information Retrieval, Information Structure, And Information Agents, Daniela Rus, Devika Subramanian
Information Retrieval, Information Structure, And Information Agents, Daniela Rus, Devika Subramanian
Computer Science Technical Reports
This paper presents a customizable architecture for software agents that capture and access information in large, heterogeneous, distributed electronic repositories. The key idea is to exploit underlying structure at various levels of granularity to build high-level indices with task-specific interpretations. Information agents construct such indices and are configured as a network of reusable modules called structure detectors and segmenters. We illustrate our architecture with the design and implementation of smart information filters in two contexts: retrieving stock market data from Internet newsgroups, and retrieving technical reports from Internet ftp sites.
An Api For Choreographing Data Accesses, Elizabeth A.M. Shriver, Leonard F. Wisniewski
An Api For Choreographing Data Accesses, Elizabeth A.M. Shriver, Leonard F. Wisniewski
Computer Science Technical Reports
Current APIs for multiprocessor multi-disk file systems are not easy to use in developing out-of-core algorithms that choreograph parallel data accesses. Consequently, the efficiency of these algorithms is hard to achieve in practice. We address this deficiency by specifying an API that includes data-access primitives for data choreography. With our API, the programmer can easily access specific blocks from each disk in a single operation, thereby fully utilizing the parallelism of the underlying storage system. Our API supports the development of libraries of commonly-used higher-level routines such as matrix-matrix addition, matrix-matrix multiplication, and BMMC (bit-matrix-multiply/complement) permutations. We illustrate our API …
Complexity Analysis Of Two Permutations Used By Fast Cosine Transform Algorithms, Sean S.B. Moore, Leonard F. Wisniewski
Complexity Analysis Of Two Permutations Used By Fast Cosine Transform Algorithms, Sean S.B. Moore, Leonard F. Wisniewski
Computer Science Technical Reports
Recently developed fast cosine transform (FCT) algorithms require fewer operations than any other known general algorithm. Similar to related fast transform algorithms (e.g., the FFT), these algorithms permute the data before, during, or after the computation of the transform. The choice of this permutation may be an important consideration in reducing the complexity of the permutation algorithm. In this paper, we derive the complexity to generate the permutation mappings used in these FCT algorithms for power-of-2 data sets by representing them as linear index transformations and translating them into combinational circuits. Moreover, we show that one of these permutations not …
Finding Real-Valued Single-Source Shortest Paths In O(N^3) Expected Time, Stavros G. Kolliopoulos, Clifford Stein
Finding Real-Valued Single-Source Shortest Paths In O(N^3) Expected Time, Stavros G. Kolliopoulos, Clifford Stein
Computer Science Technical Reports
Given an $n$-vertex directed network $G$ with real costs on the edges and a designated source vertex $s$, we give a new algorithm to compute shortest paths from $s$. Our algorithm is a simple deterministic one with $O(n^2 \log n)$ expected running time over a large class of input distributions. The shortest path problem is an old and fundamental problem with a host of applications. Our algorithm is the first strongly-polynomial algorithm in over 35 years to improve upon some aspect of the running time of the celebrated Bellman-Ford algorithm for arbitrary networks, with any type of cost assignments.
Enwrich: A Compute-Processor Write Caching Scheme For Parallel File Systems, Apratim Purakayastha, Carla Schlatter Ellis, David Kotz
Enwrich: A Compute-Processor Write Caching Scheme For Parallel File Systems, Apratim Purakayastha, Carla Schlatter Ellis, David Kotz
Dartmouth Scholarship
Many parallel scientific applications need high-performance I/O. Unfortunately, end-to-end parallel-I/O performance has not been able to keep up with substantial improvements in parallel-I/O hardware because of poor parallel file-system software. Many radical changes, both at the interface level and the implementation level, have recently been proposed. One such proposed interface is \em collective I/O, which allows parallel jobs to request transfer of large contiguous objects in a single request, thereby preserving useful semantic information that would otherwise be lost if the transfer were expressed as per-processor non-contiguous requests. Kotz has proposed \em disk-directed I/O as an efficient implementation technique for …
Expanding The Potential For Disk-Directed I/O, David Kotz
Expanding The Potential For Disk-Directed I/O, David Kotz
Dartmouth Scholarship
As parallel computers are increasingly used to run scientific applications with large data sets, and as processor speeds continue to increase, it becomes more important to provide fast, effective parallel file systems for data storage and for temporary files. In an earlier work we demonstrated that a technique we call disk-directed I/O has the potential to provide consistent high performance for large, collective, structured I/O requests. In this paper we expand on this potential by demonstrating the ability of a disk-directed I/O system to read irregular subsets of data from a file, and to filter and distribute incoming data according …
Interfaces For Disk-Directed I/O, David Kotz
Interfaces For Disk-Directed I/O, David Kotz
Computer Science Technical Reports
In other papers I propose the idea of disk-directed I/O for multiprocessor file systems. Those papers focus on the performance advantages and capabilities of disk-directed I/O, but say little about the application-programmer's interface or about the interface between the compute processors and I/O processors. In this short note I discuss the requirements for these interfaces, and look at many existing interfaces for parallel file systems. I conclude that many of the existing interfaces could be adapted for use in a disk-directed I/O system.
Structured Permuting In Place On Parallel Disk Systems, Leonard F. Wisniewski
Structured Permuting In Place On Parallel Disk Systems, Leonard F. Wisniewski
Computer Science Technical Reports
The ability to perform permutations of large data sets in place reduces the amount of necessary available disk storage. The simplest way to perform a permutation often is to read the records of a data set from a source portion of data storage, permute them in memory, and write them to a separate target portion of the same size. It can be quite expensive, however, to provide disk storage that is twice the size of very large data sets. Permuting in place reduces the expense by using only a small amount of extra disk storage beyond the size of the …
Process Migration For Heterogeneous Distributed Systems, Matt Bishop, Mark Valence, Leonard F. Winiewski
Process Migration For Heterogeneous Distributed Systems, Matt Bishop, Mark Valence, Leonard F. Winiewski
Computer Science Technical Reports
The policies and mechanisms for migrating processes in a distributed system become more complicated in a heterogeneous environment, where the hosts may differ in their architecture and operating systems. These distributed systems include a large quantity and great diversity of resources which may not be fully utilized without the means to migrate processes to the idle resources. In this paper, we present a graph model for single process migration which can be used for load balancing as well as other non-traditional scenarios such as migration during the graceful degradation of a host. The graph model provides the basis for a …
Fast Spherical Transforms On Distance Transitive Graphs, J R. Driscoll, D M. Healy Jr, D Rockmore
Fast Spherical Transforms On Distance Transitive Graphs, J R. Driscoll, D M. Healy Jr, D Rockmore
Computer Science Technical Reports
No abstract provided.
Disk-Directed I/O For An Out-Of-Core Computation, David Kotz
Disk-Directed I/O For An Out-Of-Core Computation, David Kotz
Dartmouth Scholarship
New file systems are critical to obtain good I/O performance on large multiprocessors. Several researchers have suggested the use of \em collective\/ file-system operations, in which all processes in an application cooperate in each I/O request. Others have suggested that the traditional low-level interface (\tt read, write, seek) be augmented with various higher-level requests (e.g., \em read matrix). Collective, high-level requests permit a technique called \em disk-directed I/O\/ to significantly improve performance over traditional file systems and interfaces, at least on simple I/O benchmarks. In this paper, we present the results of experiments with an “out-of-core” LU-decomposition program. Although its …
Deciding Finiteness For Matrix Groups Over Function Fields, Robert Beals, Daniel N. Rockmore, Ki-Seng Tan
Deciding Finiteness For Matrix Groups Over Function Fields, Robert Beals, Daniel N. Rockmore, Ki-Seng Tan
Computer Science Technical Reports
Let S be any finite subset GLn(F(t)) where F is a field. In this paper we give algorithms to decide if the group generated by S is finite. In the case of characteristic zero, slight modifications of earlier work of Babai, Beals and Rockmore [1] give polynomial time deterministic algorithms to solve this problem. The case of positive characteristic turns out to be more subtle and our algorithms depend on a structure theorem proved here, generalizing a theorem of Weil. We also present a fairly detailed analysis of the size of finite subgroups in this case and give bounds which …
A Multiple Discrete Pass Algorithm On A Dec Alpha 2100, Scott R. Cushman
A Multiple Discrete Pass Algorithm On A Dec Alpha 2100, Scott R. Cushman
Dartmouth College Undergraduate Theses
No abstract provided.
Simulation Of A Video-On-Demand System, Song Bac Toh
Simulation Of A Video-On-Demand System, Song Bac Toh
Dartmouth College Undergraduate Theses
This paper presents a simulation study of a video-on-demand system. The focus of the study is the effectiveness of different caching strategies on a video-on-demand system with two levels of cache, RAM and disks, in front of a tape library. Using an event-driven simulator, I show that caching was helpful in increasing the service capacity of the system. On-demand caching showed its advantages especially when the requests were clustered around a few popular titles (in other words, there was temporal locality).
Tias: A Transportable Intelligent Agent System, Kenneth Harker
Tias: A Transportable Intelligent Agent System, Kenneth Harker
Dartmouth College Undergraduate Theses
In recent years, there has been an explosive growth in the amount of information available to our society. In particular, the amount of information available on-line through vast networks like the global Internet has been growing at a staggering rate. This growth rate has by far exceeded the rate of growth in network speeds, as has the number of individuals and organizations seeking access to this information. There is thus a motivation to find abstract methods of manipulating this on-line data in ways that both serve the needs of end users efficiently and use network resources intelligently. In lieu of …
Ph.D. Thesis Proprosal: Transportable Agents, Robert S. Gray
Ph.D. Thesis Proprosal: Transportable Agents, Robert S. Gray
Computer Science Technical Reports
One of the paradigms that has been suggested for allowing efficient access to remote resources is transportable agents. A transportable agent is a named program that can migrate from machine to machine in a heterogeneous network. The program chooses when and where to migrate. It can suspend its execution at an arbitrary point, transport to another machine and resume execution on the new machine. Transportable agents have several advantages over the traditional client/server model. Transportable agents consume less network bandwidth and do not require a connection between communicating machines -- this is attractive in all networks and particularly attractive in …
Low-Level Interfaces For High-Level Parallel I/O, Nils Nieuwejaar, David Kotz
Low-Level Interfaces For High-Level Parallel I/O, Nils Nieuwejaar, David Kotz
Dartmouth Scholarship
As the I/O needs of parallel scientific applications increase, file systems for multiprocessors are being designed to provide applications with parallel access to multiple disks. Many parallel file systems present applications with a conventional Unix-like interface that allows the application to access multiple disks transparently. By tracing all the activity of a parallel file system in a production, scientific computing environment, we show that many applications exhibit highly regular, but non-consecutive I/O access patterns. Since the conventional interface does not provide an efficient method of describing these patterns, we present three extensions to the interface that support \em strided, \em …
Exploring The Use Of I/O Nodes For Computation In A Mimd Multiprocessor, David Kotz, Ting Cai
Exploring The Use Of I/O Nodes For Computation In A Mimd Multiprocessor, David Kotz, Ting Cai
Dartmouth Scholarship
As parallel systems move into the production scientific-computing world, the emphasis will be on cost-effective solutions that provide high throughput for a mix of applications. Cost-effective solutions demand that a system make effective use of all of its resources. Many MIMD multiprocessors today, however, distinguish between “compute” and “I/O” nodes, the latter having attached disks and being dedicated to running the file-system server. This static division of responsibilities simplifies system management but does not necessarily lead to the best performance in workloads that need a different balance of computation and I/O. \par Of course, computational processes sharing a node with …
Expanding The Potential For Disk-Directed I/O, David Kotz
Expanding The Potential For Disk-Directed I/O, David Kotz
Computer Science Technical Reports
As parallel computers are increasingly used to run scientific applications with large data sets, and as processor speeds continue to increase, it becomes more important to provide fast, effective parallel file systems for data storage and for temporary files. In an earlier work we demonstrated that a technique we call disk-directed I/O has the potential to provide consistent high performance for large, collective, structured I/O requests. In this paper we expand on this potential by demonstrating the ability of a disk-directed I/O system to read irregular subsets of data from a file, and to filter and distribute incoming data according …
Content-Based Image Retrieval: Color And Edges, Robert S. Gray
Content-Based Image Retrieval: Color And Edges, Robert S. Gray
Computer Science Technical Reports
One of the tools that will be essential for future electronic publishing is a powerful image retrieval system. The author should be able to search an image database for images that convey the desired information or mood; a reader should be able to search a corpus of published work for images that are relevant to his or her needs. Most commercial image retrieval systems associate keywords or text with each image and require the user to enter a keyword or textual description of the desired image. This text-based approach has numerous drawbacks -- associating keywords or text with each image …