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Large scale video streaming over the Internet requires a large amount of resources such as server I/O bandwidth and network
bandwidth. A number of video delivery techniques can be used to lower these requirements. Periodic broadcast by a central
server combined with proxy caching offers a significant reduction of the aggregate network and server I/O bandwidth usage.
However, the resources available to a single server are still limited. In this paper we propose a system with multiple geographically distributed servers. The problem of multiple servers for periodic broadcast is quite different from the problem of object location for multiple
web servers. Multiple servers offer increased amount of resources and service availability and may potentially allow a further
reduction of network bandwidth usage. On the other hand, the benefit of periodic broadcast mostly comes from high demand videos.
With multiple servers holding a video, the demand of the video at each server is reduced. Therefore, it is a challenge to
use multiple servers efficiently. We first analyze the dependence of the resource requirements on the number and locations
of the servers. Based on the character of the function describing such a dependence, we formulate and solve the problem of
video location and delivery, in a way that minimizes resource usage. We explore a trade-off between network and I/O bandwidth
requirements. We evaluate our proposed solutions through a number of tests.
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David H. C. DuEmail: |
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M Gent J Kusmierek 《Canadian Metallurgical Quarterly》1998,8(5):303; author reply 303-303; author reply 304
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Electrochemical discolouration and degradation of reactive dichlorotriazine dyes: reaction pathways 总被引:2,自引:0,他引:2
Elzbieta Kusmierek Ewa Chrzescijanska Magdalena Szadkowska-Nicze Joanna Kaluzna-Czaplinska 《Journal of Applied Electrochemistry》2011,41(1):51-62
Results of electrochemical oxidation of two reactive dichlorotriazine dyes: Reactive Red 2 and Reactive Blue 81, are presented
in this paper. Two electrode materials: Ti/TiO2(70%)–RuO2(30%) and carbon felt, were applied in the investigations as anodes. Voltammetric measurements show that Reactive Blue 81
electrooxidation proceeds easier and with higher rate than electrooxidation of Reactive Red 2. Both dyes are oxidised irreversibly
in at least one electrode step before oxygen evolution starts at the electrode. Effectiveness of electrochemical oxidation
under potentiostatic conditions achieved for Reactive Blue 81 was higher than for Reactive Red 2, with application of a carbon
felt anode. Pulse radiolysis measurements prove addition of •OH radical to the dye molecule and formation of cyclohexadienyl and naphthoxyl radicals. Results of voltammetric analysis,
pulse radiolysis measurements and GC–MS identification of intermediate products suggest two possible pathways of the dyes
electrochemical oxidation. 相似文献
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Service replication is an effective way to address resource requirements and resource availability problem. Dynamic service
selection enables clients to choose a server offering the best performance. Proper server selection is especially important
for video streaming over the Internet due to its high bandwidth requirements. However, given the length of a typical video
transmission, the server priorly selected may no longer be an optimal one for the duration of the entire transmission. More
importantly, a server may fail during the transmission of a video. In this paper we examine the possibility of switching to
another server during an on-going transmission for Periodic Broadcast schemes. Due to the timing requirements typical for
Periodic Broadcast the server switch may cause playback disruptions. We analyze the magnitude of the problem and propose an
easy to implement solution. We define the criteria, additional to the bandwidth availability for example, according to which
a new server should be selected. The client is also required to delay its playback by the amount of time bounded by the server
transmission offset. In addition, we propose an alternative method to ensure uninterrupted playback that relies on proxy caching.
Simulation results show that our approach can significantly reduce the likelihood of playback disruptions.
相似文献
David H. C. DuEmail: |
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In this paper, we propose a Loopback approach in a two-level streaming architecture to exploit collaborative client/proxy buffers for improving the quality and efficiency of large-scale streaming applications. At the upper level we use a content delivery network (CDN) to deliver video from a central server to proxy servers. At the lower level a proxy server delivers video with the help of collaborative client caches. In particular, a proxy server and its clients in a local domain cache different portions of a video and form delivery loops. In each loop, a single video stream originates at the proxy, passes through a number of clients, and finally is passed back to the proxy. As a result, with limited bandwidth and storage space contributed by collaborative clients, we are able to significantly reduce the required network bandwidth, I/O bandwidth, and cache space of a proxy. Furthermore, we develop a local repair scheme to address the client failure issue for enhancing service quality and eliminating most required repairing load at the central server. For popular videos, our local repair scheme is able to handle most of single-client failures without service disruption and retransmissions from the central server. Our analysis and simulations have shown the effectiveness of the proposed scheme. 相似文献
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