82838
Designs of high quality streaming proxy systems
Researchers often use segment-based proxy caching strategies to deliver streaming media by partially caching media objects. The existing strategies mainly consider increasing the byte hit ratio and/or reducing the client perceived startup latency (denoted by the metric delayed startup ratio). However, these efforts do not guarantee continuous media delivery because the to-be-viewed object segments may not be cached in the proxy when they are demanded. The potential consequence is playback jitter at the client side due to proxy delay in fetching the uncached segments, which we call proxy jitter. Thus, for the best interests of clients, a correct model for streaming proxy system design should aim to minimize proxy jitter subject to reducing the delayed startup ratio and increasing the byte hit ratio. However, we have observed two major pairs of conflicting interests inherent in this model: (1) one between improving the byte hit ratio and reducing proxy jitter, and (2) the other between improving the byte hit ratio and reducing the delayed startup ratio. In this study, we first propose an active prefetching method for in-time prefetching of uncached segments, which provides insights into the first pair of conflicting interests. Second, we further improve our lazy-segmentation scheme which effectively addresses the second pair of the conflicting interests. Finally, considering our main objective of minimizing proxy jitter and optimizing the two trade-offs, we propose a new streaming proxy system called Hyper Proxy by effectively coordinating both prefetching and segmentation techniques. Synthetic and real workloads are used to systematically evaluate our system. The performance results show that the hyper proxy system generates minimum proxy jitter with a low delayed startup ratio and a small decrease of byte hit ratio compared with existing schemes
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
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.
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.
8429922
ASAP: an AS-Aware Peer-Relay Protocol for High Quality VoIP
Peer-to-peer (P2P) technology has been successfully applied in Internet telephony or Voice over Internet Protocol (VoIP), such as the Skype system, where P2P is used for both searching clients and relaying voice packets. Selecting one or multiple suitable peers to relay voice packets is a critical factor for the quality, scalability and cost of a VoIP system. In this paper, we first present two sets of intensive Internet measurement results to confirm the benefits gained by peer relays in VoIP, and to investigate the performance of the Skype system. We obtain the following results: (1) many relay peer selections are suboptimal; (2) the waiting time to select a relay node can be quite long; and (3) there are a large number of unnecessary probes, resulting in heavy network traffic to limit scalability of the VoIP system. Our further analysis shows that two main reasons cause these problems. First, the peer selections do not take Autonomous System (AS) topology into consideration, and second, the complex communication relationships among peers are not well utilized. Motivated by our measurements and analysis, we propose an AS-aware peer-relay protocol called ASAP. Our objective is to significantly improve VoIP quality and system scalability with low overhead. Our intensive evaluation by trace-driven simulation shows ASAP is highly effective and easy to implement on the Internet for building large and scalable VoIP systems.
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.
3393161
BIG: An agent for resource-bounded information gathering and decision making
Abstract The World Wide Web has become an invaluable information resource but the explosion of available information has made Web search a time consuming and complex process. The large number of information sources and their different levels of accessibility, reliability and associated costs present a complex information gathering control problem. This paper describes the rationale, architecture, and implementation of a next generation information gathering system—a system that integrates several areas of Artificial Intelligence research under a single umbrella. Our solution to the information explosion is an information gathering agent, BIG, that plans to gather information to support a decision process, reasons about the resource trade-offs of different possible gathering approaches, extracts information from both unstructured and structured documents, and uses the extracted information to refine its search and processing activities.
10794655
AMPS: a flexible, scalable proxy testbed for implementing streaming services
We present the design, implementation, and performance evaluation of AMPS --- a flexible, scalable proxy testbed that supports a wide and extensible set of next-generation proxy streaming services. AMPS employs a modular architecture and is built on top of a commodity Linux system. We study the performance of AMPS proxy using a server-proxy-client configuration in a switched-Gigabit LAN environment. We identify the CPU to be the system bottleneck. Through profiling study, we further identify the kernel network protocol processing and the Network Reception Module inside the proxy to be the most CPU-intensive components. We also quantify the maximum achievable throughput for two of the principal components of the proxy - the control plane and data plane, and characterize the end-to-end performance along the server-to-proxy-to-client path. We discuss lessons learned and the various optimizations made in the course of our study to improve system performance.
8880653
Capacitated facility location problem with general setup cost
This paper presents an extension of the capacitated facility location problem (CFLP), in which the general setup cost functions and multiple facilities in one site are considered. The setup costs consist of a fixed term (site setup cost) plus a second term (facility setup costs). The facility setup cost functions are generally non-linear functions of the size of the facility in the same site. Two equivalent mixed integer linear programming (MIP) models are formulated for the problem and solved by general MIP solver. A Lagrangian heuristic algorithm (LHA) is also developed to find approximate solutions for this NP-hard problem. Extensive computational experiments are taken on randomly generated data and also well-known existing data (with some necessary modifications). The detailed results are provided and the heuristic algorithm is shown to be efficient.
33784783
A New LUT Watermarking Scheme with Near Minimum Distortion Based on the Statistical Modeling in the Wavelet Domain
This paper presents a new wavelet domain look-up table (LUT) watermarking algorithm that leads to the sub-optimal embedding of watermarks in the sense of minimizing distortion. The algorithm provides a joint distortion-robustness design of the LUT based watermark. There are two key features in the algorithm: (1) a near minimum-distortion LUT with the maximum run of 2 is designed based on the statistical properties of the wavelet coefficients; (2) an expectation-maximization (EM) algorithm based method is employed to model the statistical distribution of wavelet coefficients and select significant coefficients (coefficients with large magnitude) for watermark embedding. The experimental results show that images watermarked by the proposed algorithm have about 1.5-2.5dB peak-signal-to-noise-ratio (PSNR) gain over the conventional odd-even embedding method, while the system presents great robustness. In the case of 0.2bpp (1/40) JPEG2000 compression, the proposed scheme can ensure a reasonably low bit error rate (BER).
16218609
Exploring constraints to efficiently mine emerging patterns from large high-dimensional datasets
Emerging patterns (EPs) were proposed recently to capture changes or di erences betw een datasets: an EP is a multivariate feature whose support increases sharply from a background dataset to a target dataset, and the support ratio is called its gro wth rate. Interesting long EPs often have low support; mining such EPs from high-dimensional datasets is a great challenge due to the combinatorial explosion of the number of candidates. We propose a Constraint-based EP Miner, ConsEPMiner, that utilizes tw o types of constraints for e ectively pruning the search space: External constrain tsare user-giv enminimums on support, growth rate, and growth-rate improvement to con ne the resulting EP set. Inheren t constrain ts | same subset support, top growth rate, and same origin | are deriv ed from the propertiesof EPs and datasets, and are solely for pruning the search space and saving computation. ConsEPMiner can eÆciently mine all EPs at low support on large highdimensional datasets, with low minimums on growth rate and growth-rate improvement. In comparison, the widely known Apriori-like approach is ine ective on high-dimensional data. While ConsEPMiner adopts several ideas from DenseMiner [4], a recent constrain t-based association rule miner, its main new contributions are the introduction of inherent constrain ts and the ways to use them together with externalconstrain ts for eÆcient EP mining from dense datasets. Experiments on dense data show that, at low support, ConsEPMiner outperforms the Apriori-like approach by orders of magnitude and is more than twice as fast as the DenseMiner approach.