Abstract-The recent three years have witnessed an explosion of networked video sharing, represented by YouTube, as a new killer Internet application. Their sustainable development however is severely hindered by the intrinsic limit of their client/server architecture. A shift to the peer-to-peer paradigm has been widely suggested with success already shown in live video streaming and movie-on-demand. Unfortunately, our latest measurement demonstrates that short video clips exhibit drastically different statistics, which would simply render these existing solutions suboptimal, if not entirely inapplicable.Our long-term measurement over five million YouTube videos, on the other hand, reveal interesting social networks with strong clustering among the videos, thus opening new opportunities to explore. In this paper, we present NetTube, a novel peer-topeer assisted delivering framework that explores the clustering in social networks for short video sharing. We address a series of key design issues to realize the system, including a bi-layer overlay, an efficient indexing scheme and a pre-fetching strategy leveraging social networks. We evaluate NetTube through simulations and prototype experiments, which show that it greatly reduces the server workload, improves the playback quality and scales well.
Abstract-Broadcast is one of the most fundamental services in wireless sensor networks (WSNs). It facilitates sensor nodes to propagate messages across the whole network, serving a wide range of higher-level operations and thus being critical to the overall network design. A distinct feature of WSNs is that many nodes alternate between active and dormant states, so as to conserve energy and extend the network lifetime. Unfortunately, the impact of such cycles has been largely ignored in existing broadcast implementations that adopt the common assumption of all nodes being active all over the time.In this paper, we revisit the broadcast problem with active/dormant cycles. We show strong evidence that conventional broadcast approaches will suffer from severe performance degradation, and, under low duty-cycles, they could easily fail to cover the whole network in an acceptable timeframe. To this end, we remodel the broadcast problem in this new context, seeking a balance between efficiency and latency with coverage guarantees. We demonstrate that this problem can be translated into a graph equivalence, and develop a centralized optimal solution. It provides a valuable benchmark for assessing diverse duty-cycleaware broadcast strategies. We then extend it to an efficient and scalable distributed implementation, which relies on local information and operations only, with built-in loss compensation mechanisms.The performance of our solution is evaluated under diverse network configurations. The results suggest that our distributed solution is close to the lower bounds of both time and forwarding costs, and it well resists to the network size and wireless loss increases. In addition, it enables flexible control toward the quality of broadcast coverage.
Abstract-The Internet has become a cost-effective vehicle for software development and release, particular in the free software community. Given the free nature of this software, there are often a number of users motivated by altruism to help out with the distribution, so as to promote the healthy development of this voluntary society. It is thus naturally expected that a peer-topeer distribution can be implemented, which will scale well with large user bases, and can easily explore the network resources made available by the volunteers.Unfortunately, this application scenario has many unique characteristics, which make a straightforward adoption of existing peer-to-peer systems for file sharing (such as BitTorrent) suboptimal. In particular, a software release often consists of a large number of packages, which are difficult to distribute individually, but the archive is too large to be distributed in its entirety. The packages are also being constantly updated by the loosely-managed developers, and the interest in a particular version of a package can be very limited depending on the computer platforms and operating systems used.In this paper, we propose a novel peer-to-peer assisted distribution system design that addresses the above challenges. It enhances the existing distribution systems by providing compatible and yet more efficient downloading and updating services for software packages. Our design leads to apt-p2p, a practical implementation that extends the popular apt distributor. apt-p2p has been used in conjunction with Debian-based distribution of Linux software packages and is also available in the latest release of Ubuntu. We have addressed the key design issues in apt-p2p, including indexing table customization, response time reduction, and multi-value extension. They together ensure that the altruistic users' resources are effectively utilized and thus significantly reduces the currently large bandwidth requirements of hosting the software, as confirmed by our existing real user statistics gathered over the Internet.
The ability to predict the electrochemical performance of the cathode catalyst layer in a polymer electrolyte fuel cell hinges on a precise knowledge of water distribution and fluxes. Water transport mechanisms that must be accounted for include vapor diffusion, liquid water permeation and vaporization exchange. In order to facilitate experimental efforts to this effect, we propose an ex situ model of water fluxes in catalyst layers. The model formulation is similar to transmission line models that are widely used in the analysis of electrochemical impedance spectra of porous composite electrodes. Focusing in this article on steady state and isothermal conditions, we rationalize the response function between defined environmental conditions, i.e. gas pressures, partial vapor pressures and temperature, which are defined at the boundaries of the catalyst layer, and the net water flux. This response function provides diagnostic capabilities to isolate and extract water transport parameters of catalyst layers from measurements of water fluxes through membrane electrode assemblies or half cell systems. An important asset of the model is the ability to analyze catalyst layer transport properties under partial saturation.
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