8918525
An efficient, low-cost inconsistency detection framework for data and service sharing in an Internet-scale system
In this paper, we argue that a broad range of Internet-scale distributed applications can benefit from an underlying low-cost consistency detection framework that is an alternative to inconsistency avoidance and can detect inconsistency among nodes sharing data or services in a timely manner. This paper first presents an overview of the inconsistency detection framework. Then, it discusses the detailed design of the two-layer inconsistency detection module, the core component of this framework, which can detect inconsistency among nodes in a timely manner. The proposed two-layer inconsistency detection module is evaluated both analytically and via simulations, which shows that this module can significantly reduce the time to detect inconsistency among nodes without adding much maintenance cost. Finally, this paper outlines the possible mechanisms to discern the application semantics and to resolve the detected inconsistencies
45166966
Approximate Analysis of Multiprocessing Task Graphs
15193588
Analysis of directory based cache coherence schemes with multistage networks
Designing efficient cache coherence schemes for shared memory multiprocessors has attracted much attention of the researchers in the area. Snoopy cache protocols have been designed for bus based multiprocessors. However, the snoopy protocols are not applicable to general interconnection networks. On the other hand, the directory based cache protocols adapt very well to any kind of interconnection network such as a Multistage Network. Since different protocols have different cost overheads, and may give different performance, the protocol to be used must be wisely selected. Although there has been some simulation studies on the behavior of different directory schemes proposed in the literature, there has been no systematic analytical model for these schemes. In this paper we develop a detailed analytical model of the various directory schemes on a Multistage Interconnection Network. The shared miss ratios are computed analytically, and the performance of the various schemes is compared. Results are presented to show that the directories do not form a system bottleneck contrary to popular belief.
15655964
A partial-multiple-bus computer structure with improved cost effectiveness
This paper addresses the design and performance analysis of partial-multiple-bus interconnection networks. One such structure, called processor-oriented partial-multiple-bus (or PPMB), is proposed. It serves as an alternative to the conventional structure called memory-oriented partial-multiple-bus (or MPMB) and is aimed at higher system performance at less or equal system cost. PPMB's structural feature, which distinguishes itself from the conventional, is to provide every memory module with B paths to processors (where B is the total number of buses). This in contrast to the mere B/g paths provided in the conventional MPMB structure (where g is the number of groups), suggests a potential for higher system bandwidth. This potential is fully fulfilled by the load-balancing arbitration mechanism suggested, which in turn highlights the advantages of the proposed structure. As a result, it has been shown, both analytically and by simulation, that a substantial increase in system bandwidth (up to 20%) is achieved by the PPMB structure over the MPMB structure. In addition to the fact that the cost of PPMB is less than, or equal to, that of MPMB, its reliability is shown to be slightly increased as well.
179733
Exploiting redundancy to boost performance in a RAID-10 style cluster-based file system
While aggregating the throughput of existing disks on cluster nodes is a cost-effective approach to alleviate the I/O bottleneck in cluster computing, this approach suffers from potential performance degradations due to contentions for shared resources on the same node between storage data processing and user task computation. This paper proposes to judiciously utilize the storage redundancy in the form of mirroring existed in a RAID-10 style file system to alleviate this performance degradation. More specifically, a heuristic scheduling algorithm is developed, motivated from the observations of a simple cluster configuration, to spatially schedule write operations on the nodes with less load among each mirroring pair. The duplication of modified data to the mirroring nodes is performed asynchronously in the background. The read performance is improved by two techniques: doubling the degree of parallelism and hot-spot skipping. A synthetic benchmark is used to evaluate these algorithms in a real cluster environment and the proposed algorithms are shown to be very effective in performance enhancement.
1546029
Design and Analysis of Hierarchical Ring Networks for Shared-Memory Multiprocessors
ÐWe study four augmentations of ring networks which are intended to enhance a ring's efficiency as a communication medium significantly, while increasing its structural complexity only modestly. Chordal rings add ashortcuto edges, which can be viewed as chords, to the ring. Express rings are chordal rings whose chords are routed outside the ring. Multirings append subsidiary rings to edges of a ring and, recursively, to edges of appended subrings. Hierarchical ring networks (HRN's) append subsidiary rings to nodes of a ring and, recursively, to nodes of appended subrings. We show that these four modes of augmentation are very closely related: 1) Planar chordal rings, planar express rings, and multirings are topologically equivalent families of networks with the acutwidtho of an express ring translating into the atree deptho of its isomorphic multiring and vice versa. 2) Every depth-d HRN is a spanning subgraph of a depth-2dÿ 1 multiring. 3) Every depth-d multiring M can be embedded into a d-dimensional mesh with dilation 3 in such a way that some node of M resides at a corner of the mesh. 4) Every depth-d HRN H can be embedded into a d-dimensional mesh with dilation 2 in such a way that some node of H resides at a corner of the mesh. In addition to demonstrating that these four augmented ring networks are grid graphs, our embedding results afford us close bounds on how much decrease in diameter is achievable for a given increase in structural complexity for the networks. Specifically, we derive upper and lower bounds on the optimal diameters of N-node depth-d multirings and HRNs that are asymptotically tight for large N and d. Index TermsÐRing networks, chordal rings, express rings, multirings, hierarchical ring networks, grid graphs, graph embedding, diameter trade-offs.
16906364
Scalable and Robust Aggregation Techniques for Extracting Statistical Information in Sensor Networks
Wireless sensor networks have stringent constraints on system resources and data aggregation techniques are critically important. However, accurate data aggregation is difficult due to the variation of sensor readings and due to the frequent communication failures. To address these difficulties, we propose a scalable and robust data aggregation algorithm. The novelty of our work includes two aspects. First, our algorithm exploits the mixture model and the Expectation Maximization (EM) algorithm for parameter estimation. Hence, it captures the effects of aggregation over different scales while keeping the communication cost low. Second, our algorithm exploits loss-tolerant multi-path routing schemes. Hence, it obtains accurate statistical information even in the presence of high link and node failure rates. We demonstrate that our techniques reduce communication cost while retaining the precious statistical information otherwise neglected by other aggregation techniques. Our evaluation shows the proposed techniques are robust against link and node failures, and perform consistently well.
20921565
Dynamical Process of Excitation Fusion in Polymers
Due to the confinement effect in the nondegenerate polymers and the electron-lattice interaction, the electron-hole pair forms a self-trapped single excitation. It is shown that two single excitations in one chain can fuse into one double excitation, and the relaxation time of the fusion process is about 160 fs.
16310485
Stably Computable Properties of Network Graphs
We consider a scenario in which anonymous, finite-state sensing devices are deployed in an ad-hoc communication network of arbitrary size and unknown topology, and explore what properties of the network graph can be stably computed by the devices. We show that they can detect whether the network has degree bounded by a constant d, and, if so, organize a computation that achieves asymptotically optimal linear memory use. We define a model of stabilizing inputs to such devices and show that a large class of predicates of the multiset of final input values are stably computable in any weakly-connected network. We also show that nondeterminism in the transition function does not increase the class of stably computable predicates.
18773100
An Approach to Broaden the Semantic Coverage of ACL Speech Acts
Current speech-act based ACLs specify domain-independent information about communication and relegate domain-dependent information to an unspecified content language. This is reasonable, but the ACLs cover only a small fraction of the domain-independent information possible. As a key element of modern ACLs, the set of communicative acts needs to be as complete as possible to enable agents to communicate the widest range of information with agreed-upon semantics. This paper describes a new approach to broaden the semantic coverage of ACL speech acts. It provides agents with the ability to express more of the possible meanings in human languages and yields a more powerful ACL. Specifically, we first compare Austin's and Searle's classifications, and Ballmer and Brennenstuhl's comprehensive classification of speech acts. The main meaning categories and their semantics are given next. Finally, a multifaceted evaluation of our approach is presented, which points out that the approach potentially can combine the benefits of the FIPA ACL with Ballmer and Brennenstuhl's speech act classification, resulting in a more expressive ACL.
18051966
Design and analysis of adaptive strategies for locating internet-based servers in MANETs
A critical problem in providing Internet access to Mobile Ad Hoc Networks (MANETs) is how the mobile hosts can locate Internet-based servers efficiently in a dynamic, unstructured network. This paper studies adaptive strategies that combine both proactive advertising by the servers and on-demand discovery by the mobile hosts. The adaptive strategies determine the relative rate of proactive advertising and on-demand discovery according to system characteristics such as host mobility level and offered load. Our simulation study reveals that, compared to the previous proactive strategies and reactive strategies, the adaptive strategies reduce network traffic by several times when the network has a moderate offered load and a low or high level of host mobility.