5165465
Adaptive control for packet video
Describes a portable and robust software mechanism for adaptive frame rate control for real time packet video transfer and viewing in workstation environments. No special hardware or system support is assumed. It includes (1) a responsive feedback system for dynamic presentation layer rate control in response to network load, (2) a simple and effective transport layer flow control scheme built upon an unreliable network protocol, and (3) data structures and scheduling support for integrating the rate and flow control mechanisms. The authors demonstrate that excellent jitter control is achieved by gracefully trading image resolution, and loss rates can be drastically reduced by appropriate flow control.<<ETX>>
14669009
Considering the energy consumption of mobile storage alternatives
This paper is motivated by a simple question: what are the energy consumption characteristics of mobile storage alternatives? To answer this question, we are faced with a design space of multiple dimensions. Two important dimensions are the type of storage technologies and the type of file systems. In this paper, we explore some options along each of these two dimensions. We have constructed a logical-disk system, which can be configured to run on different storage technologies and to emulate the behavior of different file systems. As we explore these configuration options, we find that the energy behavior is determined by a complex interaction of three factors: the power management mechanism of the storage device, the distribution of idleness in the workload, and the file system strategies that attempt to exploit and bridge these first two factors.
6622555
A quantitative analysis of cache policies for scalable network file systems
Current network file system protocols rely heavily on a central server to coordinate file activity among client workstations. This central server can become a bottleneck that limits scalability for environments with large numbers of clients. In central server systems such as NFS and AFS, all client writes, cache misses, and coherence messages are handled by the server. To keep up with this workload, expensive server machines are needed, configured with high-performance CPUs, memory systems, and I/O channels. Since the server stores all data, it must be physically capable of connecting to many disks. This reliance on a central server also makes current systems inappropriate for wide area network use where the network bandwidth to the server may be limited.
In this paper, we investigate the quantitative performance effect of moving as many of the server responsibilities as possible to client workstations to reduce the need for high-performance server machines. We have devised a cache protocol in which all data reside on clients and all data transfers proceed directly from client to client. The server is used only to coordinate these data transfers. This protocol is being incorporated as part of our experimental file system, xFS. We present results from a trace-driven simulation study of the protocol using traces from a 237 client NFS installation. We find that the xFS protocol reduces server load by more than a factor of six compared to AFS without significantly affecting response time or file availability.
11858758
Improving the performance of log-structured file systems with adaptive methods
File system designers today face a dilemma. A log-structured file system (LFS) can offer superior performance for many common workloads such as those with frequent small writes, read traffic that is predominantly absorbed by the cache, and sufficient idle time to clean the log. However, an LFS has poor performance for other workloads, such as random updates to a full disk with little idle time to clean. In this paper, we show how adaptive algorithms can be used to enable LFS to provide high performance across a wider range of workloads. First, we show how to improve LFS write performance in three ways: by choosing the segment size to match disk and workload characteristics, by modifying the LFS cleaning policy to adapt to changes in disk utilization, and by using cached data to lower cleaning costs. Second, we show how to improve LFS read performance by reorganizing data to match read patterns. Using trace-driven simulations on a combination of synthetic and measured workloads, we demonstrate that these extensions to LFS can significantly improve its performance.
6692312
Evaluation of architectural support for global address-based communication in large-scale parallel machines
Large-scale parallel machines are incorporating increasingly sophisticated architectural support for user-level messaging and global memory access. We provide a systematic evaluation of a broad spectrum of current design alternatives based on our implementations of a global address language on the Thinking Machines CM-5, Intel Paragon, Meiko CS-2, Cray T3D, and Berkeley NOW. This evaluation includes a range of compilation strategies that make varying use of the network processor; each is optimized for the target architecture and the particular strategy. We analyze a family of interacting issues that determine the performance trade-offs in each implementation, quantify the resulting latency, overhead, and bandwidth of the global access operations, and demonstrate the effects on application performance.
208003557
Serverless network file systems
We propose a new paradigm for network file system design: serverless network file systems. While traditional network file systems rely on a central server machine, a serverless system utilizes workstations cooperating as peers to provide all file system services. Any machine in the system can store, cache, or control any block of data. Our approach uses this location independence, in combination with fast local area networks, to provide better performance and scalability than traditional file systems. Furthermore, because any machine in the system can assume the responsibilities of a failed component, our serverless design also provides high availability via redundatn data storage. To demonstrate our approach, we have implemented a prototype serverless network file system called xFS. Preliminary performance measurements suggest that our architecture achieves its goal of scalability. For instance, in a 32-node xFS system with 32 active clients, each client receives nearly as much read or write throughput as it would see if it were the only active client.
40944529
Symmetric Graphs of Order a Product of Two Distinct Primes
A simple undirected graph ? is said to be symmetric if its automorphism group Aut ? is transitive on the set of ordered pairs of adjacent vertices of ?, and ? is said to be imprimitive if Aut ? acts imprimitively on the vertices of ?. Let k and p be distinct primes with k < p. This paper gives a classification of all imprimitive symmetric graphs on kp vertices for k ? 5. The cases k < 5 have been treated previously by Cheng and Oxley (k = 2) and the second and third authors (k = 3), and the classification of primitive symmetric graphs on kp vertices with k ? 5 was done by the first and third authors.
1431727
Combining Flexibility and Scalability in a Peer-to-Peer Publish/Subscribe System
The content-based publish/subscribe model has been adopted by many services to deliver data between distributed users based on application-specific semantics. Two key issues in such systems, the semantic expressiveness of content matching and the scalability of the matching mechanism, are often found to be in conflict due to the complexity associated with content matching. In this paper, we present a novel content-based publish/subscribe architecture based on peer-to-peer matching trees. The system achieves scalability by partitioning the responsibility of event matching to self-organized peers while allowing customizable matching functionalities. Experimental results using a variety of real world datasets demonstrate the scalability and flexibility of the system.
5802618
Improving the performance of coded FDFR multi-antenna systems with turbo-decoding
A full-diversity full-rate (FDFR) design was developed recently, to enable an uncoded layered space-time (LST) system to achieve full-diversity (N/sub t/N/sub r/) and full-rate (N/sub t/ symbols per channel use) simultaneously, for any number of transmit antennas N/sub t/ and receive antennas N/sub r/. We investigate the performance of a coded FDFR system obtained by concatenating an error control coding (ECC) module and an FDFR module with a random interleaver in between. Iterative decoding is performed at the receiver. With R/sub c/ denoting the ECC rate, and d the minimum Hamming distance, an over-all transfer rate of R/sub c/N/sub t/ symbols per channel use and a full diversity order dN/sub t/N/sub r/ are achieved. Compared with coded V-BLAST, without sacrificing rate the coded FDFR system offers evident performance improvement when relatively weak codes are used. As N/sub r/ increases, even such a strong code as rate 1/2 turbo codes can benefit from FDFR. Specifically, 1.5 dB gain over coded V-BLAST is obtained in a 2 /spl times/ 2 antenna setup when convolutional codes or rate 3/4 turbo codes are used. 0.5 dB gain is offered in a 2 /spl times/ 5 setup when rate 1/2 turbo code is used. The price paid is increased complexity.
36876991
Cooperative dynamics coordinated by stochastic noise in a multi-cell system
We investigate a general coupled noisy system with time delays for cooperative behavior in a multi-cell system. The main conclusion is that appropriate noise intensity and coupling are capable of driving the coupled system to synchrony or resonance, which may be exploited by biological organisms actively to facilitate mutual communication. A multi-cell system with a synthetic gene network, which consists of both intracellular and extracellular noise and time delays, is adopted to demonstrate the effect of noise and coupling on collective dynamics.
35854986
News Headline Generation based on Linguistic Methods