13613044
Low-Cost and Reliable Mutual Anonymity Protocols in Peer-to-Peer Networks
We present several protocols to achieve mutual communication anonymity between an information requester and a provider in a P2P information-sharing environment, such that neither the requester nor the provider can identify each other, and no other peers can identify the two communicating parties with certainty. Most existing solutions achieve mutual anonymity in pure P2P systems without any trusted central controls. Compared with two such representative ones, our protocols improve efficiency in two different ways. First, utilizing trusted third parties and aiming at both reliability and low-cost, we propose a group of mutual anonymity protocols. We show that with some limited central support, our protocols can accomplish the goals of anonymity, efficiency, and reliability. Second, we propose a mutual anonymity protocol which relies solely on self-organizations among peers without any trusted central controls. In this protocol, the returning path can be shorter than the requesting path. This protocol does not need to broadcast the requested file back to the requester so that the bandwidth is saved and efficiency is improved. In addition, this protocol does not need special nodes to keep indices of sharing files, thus eliminating the index maintenance overhead and the potential for inconsistency between index records and peer file contents. We have evaluated our techniques in a browser-sharing environment. We show that the average increase in response time caused by our protocols is negligible, and these protocols show advantages over existing protocols in a P2P system.
14511182
Does internet media traffic really follow Zipf-like distribution?
It is commonly agreed that Web traffic follows the Zipf-like distribution, which is an analytical foundation for improving Web access performance by client-server based proxy caching systems on the Internet. However, some recent studies have observed non-Zipf-like distributions of Internet media traffic in different content delivery systems. Due to the variety of media delivery systems and the diversity of media content, existing studies on media traffic are largely workload specific, and the observed access patterns are often different from or even conflict with each other. For Web media systems, study [3] reports that the access pattern of streaming media is Zipf-like in a university campus network, while study [2] finds that it is not Zipf-like in an enterprise media server. For VoD media systems, study [1] finds that it is not Zipf-like in a multicast-based Media-on-Demand server of a campus network, while study [9] reports it is Zipf-like in a large VoD streaming system of an ISP. For P2P media systems, study [4] reports that the access pattern of media workload in KaZaa system collected in a campus network is not Zipf-like, while study [5] reports that it is Zipf-like in another campus network. For live streaming media systems, study [8] reports it is Zipf-like while study [6] reports it is not Zipf-like. A number of models have been proposed to explain the observed media access patterns, such as the generalized Zipf-like model [7], “fetch-at-most-once” model [4], and two-mode Zipf model [6]. However, each of these models can only explain a very limited scope of measurement results. A general model of Internet media access patterns is highly desirable for traffic engineering on the Internet and is critical to design, benchmark, and evaluate Internet media delivery systems. In this study, we have analyzed a wide variety of media workloads on the Internet. The workloads were collected from both the client side and the server side in Web, VoD, P2P, and live streaming environments between 1998 and 2006, where the media content is delivered via Web/P2P downloading or unicast/multicast streaming. The duration of these workloads ranges from a few days to more than two years and the user population ranges from several thousands to more than one hundred thousand. The number of client requests
10102756
Semi-Empirical Multiprocessor Performance Predictions
This paper presents a multiprocessor performance prediction methodology supported by experimental measurements, which predicts the execution time of large application programs on large parallel architectures based on a small set of sample data. We propose a graph model to describe application program behavior. In order to precisely abstract an architecture model for the prediction, important and implicit architecture parameters are obtained by experiments. We focus on performance predictions of application programs in shared-memory and data-parallel architectures. Real world applications are implemented using the shared-memory model on the KSR-1 and using the data-parallel model on the CM-5 for performance measurements and prediction validation. We show that experimental measurements provide strong support for performance predictions on multiprocessors with implicit communications and complex memory systems, such as shared-memory and data-parallel systems, while analytical techniques partially applied in the prediction significantly reduce computer simulation and measurement time.
7906272
Coordinating Parallel Processes on Networks of Workstations
The network of workstations (NOW) we consider for scheduling is heterogeneous and nondedicated, where computing power varies among the workstations and local and parallel jobs may interact with each other in execution. An effective NOW scheduling scheme needs sufficient information about system heterogeneity and job interactions. We use the measured power weight of each workstation to quantify the differences of computing capability in the system. Without a processing power usage agreement between parallel jobs and local user jobs in a workstation, job interactions are unpredictable, and performance of either type of jobs may not be guaranteed. Using the quantified and deterministic system information, we design a scheduling scheme calledself-coordinated local schedulingon a heterogeneous NOW. Based on a power usage agreement between local and parallel jobs, this scheme coordinates parallel processes independently in each workstation based on the coscheduling principle. We discuss its implementation on Unix System V Release 4 (SVR4). Our simulation results on a heterogeneous NOW show the effectiveness of the self-coordinated local scheduling scheme.
1520083
Token-ordered LRU: an effective page replacement policy and its implementation in Linux systems
Most computer systems use a global page replacement policy based on the LRU principle to approximately select a Least Recently Used page for a replacement in the entire user memory space. During execution interactions, a memory page can be marked as LRU even when its program is conducting page faults. We define the LRU pages under such a condition as false LRU pages because these LRU pages are not produced by program memory reference delays, which is inconsistent with the LRU principle. False LRU pages can significantly increase page faults, even cause system thrashing. This poses a more serious risk in a large parallel systems with distributed memories because of the existence of coordination among processes running on individual node. In the case, the process thrashing in a single node or a small number of nodes could severely affect other nodes running coordinating processes, even crash the whole system. In this paper, we focus on how to improve the page replacement algorithm running on one node. After a careful study on characterizing the memory usage and the thrashing behaviors in the multi-programming system using LRU replacement. we propose an LRU replacement alternative, called token-ordered LRU, to eliminate or reduce the unnecessary page faults by effectively ordering and scheduling memory space allocations. Compared with traditional thrashing protection mechanisms such as load control, our policy allows more processes to keep running to support synchronous distributed process computing. We have implemented the token-ordered LRU algorithm in a Linux kernel to show its effectiveness.
6763495
Memory Hierarchy Considerations for Cost-Effective Cluster Computing
Using off-the-shelf commodity workstations and PCs to build a cluster for parallel computing has become a common practice. The cost-effectiveness of a cluster computing platform for a given budget and for certain types of applications is mainly determined by its memory hierarchy and the interconnection network configurations of the cluster. Finding such a cost-effective solution from exhaustive simulations would be highly time-consuming and predictions from measurements on existing clusters would be impractical. We present an analytical model for evaluating the performance impact of memory hierarchies and networks on cluster computing. The model covers the memory hierarchy of a single SMP, a cluster of workstations/PCs, or a cluster of SMPs by changing various architectural parameters. Network variations covering both bus and switch networks are also included in the analysis. Different types of applications are characterized by parameterized workloads with different computation and communication requirements. The model has been validated by simulations and measurements. The workloads used for experiments are both scientific applications and commercial workloads. Our study shows that the depth of the memory hierarchy is the most sensitive factor affecting the execution time for many types of workloads. However, the interconnection network cost of a tightly coupled system with a short depth in memory hierarchy, such as an SMP, is significantly more expensive than a normal cluster network connecting independent computer nodes. Thus, the essential issue to be considered is the trade-off between the depth of the memory hierarchy and the system cost. Based on analyses and case studies, we present our quantitative recommendations for building cost-effective clusters for different workloads.
8738797
Applying database support for large scale data driven science in distributed environments
There is a rapidly growing set of applications, referred to as data driven applications, in which analysis of large amounts of data drives the next steps taken by the scientist, e.g., running new simulations, doing additional measurements, extending the analysis to larger data collections. Critical steps in data analysis are to extract the data of interest from large and potentially distributed datasets and to move it from storage clusters to compute clusters for processing. We have developed a middleware framework, called GridDB-Lite, that is designed to efficiently support these two steps. We describe the application of GridDB-Lite in large scale oil reservoir simulation studies and experimentally evaluate several optimizations that can be employed in the GridDB-Lite runtime system.
12293880
Enhancing data authenticity and integrity in P2P systems
Peer-to-peer systems let users share information in distributed environments because of their scalability and efficiency. However, existing P2P systems are vulnerable to numerous security attacks and lack a mechanism to ensure shared information's authenticity and integrity. A proposed general architecture enhances these aspects by leveraging trusted computing technology, which is built on a trusted platform module and provides a mechanism for building trust into the application layer. Preliminary experimental results show that the proposed scheme can ensure data authenticity and integrity in P2P systems with acceptable performance overhead.
30931074
A Distributed Object Database's Basic Design Issues
1109125
An on-demand Bluetooth scatternet formation and routing protocol for wireless sensor networks
Bluetooth is a promising short-range wireless communication technology with the characteristics of interference resilience and power efficiency which are required by wireless sensor networks. As an enhanced sensor node platform, the Intel Mote uses Bluetoth as its radio scheme and MAC protocol. However, most of the existing scatternet formation protocols intend to connect all the nodes within the networks regardless of traffic pattern. For wireless sensor network applications with traffic of low duty cycle, on-demand scatternet formation and routing achieve significant power saving by avoiding to maintain the entire network connectivity. We propose in this paper an on-demand scatternet and route formation protocol for Bluetooth-based wireless sensor networks. It is able to cope with multiple sources initiating traffic simultaneously in densely deployed wireless sensor networks. We also introduce a modified inquiry scheme using extended ID packet for power efficient propagation of route request messages. Furthermore, we propose a mechanism employing POLL packets in Page processes to transfer scatternet formation and route reply information without extra overhead. Simulation results show that our on-demand scatternet formation and routing protocol can provide multihop channels with reasonable delay for Bluetooth-base wireless sensor networks.
10484270
Obligatory activator-polymerase addition order at promoters
The kinetics of open complex formation were measured by migration retardation assay and DNase I footprinting at the activator-dependent promoters ara P1, lac P1 and gal P1. In each case, the rate of open complex formation was significantly faster if the activator, AraC for ara and CAP for lac and gal, had been added before RNA polymerase. The results indicate that complexes of transcriptional activators, RNA polymerase and promoter can exist in two states, one which can form open complexes rapidly and one which cannot.