P2P流媒体cache是一种有效减少带宽开销、提高对象利用率的技术,通常采用FIFO,LRU等算法置换内容.然而,流媒体不同于Web对象,P2P网络也有别于客户/服务器模式.在分布式应用中这些算法可能影响系统的性能,为此,分析了FIFO和LRU置换算法,提出了基于供求关系的SD算法,以及基于分片副本数量的REP算法,并对其进行评估和比较.针对不同的节点到达间隔,将SD和REP同FIFO,LRU进行比较,发现在启动延迟、媒体副本数量和根节点依赖度方面SD和REP几乎均优于FIFO和LRU.同LSB(least sent bytes)算法相比,某些场景中SD的启动延迟减少了约40%,而REP在副本数量方面远远超过LSB的结果,说明在P2P网络流媒体服务中使用SD和REP缓存置换算法有助于提高系统性能.
Real-time applications are sensitive to conditions such as transmission delay and jittering. To cut down on the influence generated by the WLAN handoff process, three parts of WLAN （wireless local area networks） han...
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Real-time applications are sensitive to conditions such as transmission delay and jittering. To cut down on the influence generated by the WLAN handoff process, three parts of WLAN （wireless local area networks） handoff： handoff triggering, access point selection and the fast handoff algorithm are investigated. A fast handoff solution totally based on the station is proposed and it is composed of three parts： a handoff triggering mechanism based on dynamic threshold adjustment; an AP selection criterion based on probe delay; a fast handoff algorithm with differentiated channel selection and a dynamic cache. The station based solution is independent with AP＇s collaboration and avoids any changes in the IEEE 802. l l protocol. It is robust and has very good extensibility. Through tests and evaluation in a hotspot WLAN, the solution effectively reduces handoff latency and user experience of real-time applications is enhanced.
The design and evaluation of accelerated transmission （AT） systems in peer-to-peer networks for data transmission are introduced. Based on transfer control protocol （TCP） and peer-to-peer （P2P） substrate network...
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The design and evaluation of accelerated transmission （AT） systems in peer-to-peer networks for data transmission are introduced. Based on transfer control protocol （TCP） and peer-to-peer （P2P） substrate networks, AT can select peers of high performance quality, monitor the transfer status of each peer, dynamically adjust the transmission velocity and react to connection degradation with high accuracy and low overhead. The system performance is evaluated by simulations, and the interrelationship between network flow, bandwidth utilities and network throughput is analyzed. Owing to the collaborative operation of neighboring peers, AT accelerates the process of data transmission and the collective network performance is much more satisfactory.
Based on the advantages of both Grid and peer-to-peer （P2P） networks, an overlay network in the Grid environment is constructed by P2P technologies by a modified version of the Chord protocol. In this mechanism, dif...
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Based on the advantages of both Grid and peer-to-peer （P2P） networks, an overlay network in the Grid environment is constructed by P2P technologies by a modified version of the Chord protocol. In this mechanism, different nodes＇ accesses to different resources are determined by their contribution. Therefore, the heterogeneous resources of virtual organizations in large-scale Grid can be effectively integrated, and the key node failure as well as system bottleneck in the traditional Grid environment is eliminated. The experimental results indicate that this management mechanism can achieve better average performance in the Grid environment and maintain the P2P characteristics as well.
The model of energy cost in a wireless sensor network （WSN）environment is built, and the energy awareness and the wireless interference mainly due to different path loss models are studied. A special case of a clust...
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The model of energy cost in a wireless sensor network （WSN）environment is built, and the energy awareness and the wireless interference mainly due to different path loss models are studied. A special case of a clustering scheme, a twodimensional grid clustering mechanism, is adopted. Clusterheads are rotated evenly among all sensor nodes in an efficient and decentralized manner, based on the residual energy in the battery and the random backoff time. In addition to transmitting and receiving packets within the sensors＇ electrical and amplification circuits, extra energy is needed in the retransmission of packets due to packet collisions caused by severe interference. By analysis and mathematical derivation, which are based on planar geometry, it is shown that the total energy consumed in the network is directly related to the gridstructure in the proposed grid based clustering mechanism. The transmission range is determined by cluster size, and the path loss exponent is determined by nodal separation. The summation of overall interference is caused by all the sensors that are transmitting concurrently. By analysis and simulation, an optimal grid structure with the corresponding grid size is presented, which balances between maximizing energy conservation and minimizing overall interference in wireless sensor networks.
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