How to process aggregate queries over data streams efficiently and effectively have been becoming hot re search topics in both academic community and industrial community. Aiming at the issues, a novel Linked-tree alg...How to process aggregate queries over data streams efficiently and effectively have been becoming hot re search topics in both academic community and industrial community. Aiming at the issues, a novel Linked-tree algorithm based on sliding window is proposed in this paper. Due to the proposal of concept area, the Linked-tree algorithm reuses many primary results in last window and then avoids lots of unnecessary repeated comparison operations between two successive windows. As a result, execution efficiency of MAX query is improved dramatically. In addition, since the size of memory is relevant to the number of areas but irrelevant to the size of sliding window, memory is economized greatly. The extensive experimental results show that the performance of Linked-tree algorithm has significant improvement gains over the traditional SC （Simple Compared） algorithm and Ranked-tree algorithm.展开更多
Vehicular ad hoc networks(VANETs)support safety-and non-safety-related applications that require the transmission of emergency safety messages and periodic beacon messages.The dedicated short-range communication(DSRC)...Vehicular ad hoc networks(VANETs)support safety-and non-safety-related applications that require the transmission of emergency safety messages and periodic beacon messages.The dedicated short-range communication(DSRC)standard in VANETs is used to exchange safety messages,and is involved in multi-hop data dissemination and routing.Many researchers have focused either on emergency data dissemination or routing,but both are critical.Routing protocols are commonly used for position-based routing and distancebased routing.This paper focuses on both emergency data dissemination and multi-hop routing,with the selection of the best data disseminator and trustworthy forwarder.To select the best forwarder,ring partitioning is performed,which segregates vehicles into rings based on the coverage area for routing.Each partition is selected with a best forwarder,which minimizes the hop count for data transmission.The work also includes effective video transmission for a user’s request.Video transmission in VANETs is involved in this work to provide efficient video delivery between rapidly travelling vehicles with reduced delay owing to the selection of good-quality channels.Video transmission is prioritized according to frame types,and they are then transmitted with respect to the preference of channels.The major issue in video streaming is the loss of packets,which is our focus to minimize it.Our proposed VANET environment is simulated in OMNeT++,and the results show remarkable improvements in terms of the packet delivery ratio,end-to-end delay,and reliability.展开更多
研究了基于多级Clos数据中心网络的光电交换架构下的流量调度算法,以减少数据传输时延,同时也保证无丢包。传统ADAPT调度算法能实现加速比最小化,但仍然有一些空闲时间槽,而造成带宽未被充分利用。为了解决该问题,在多级Clos网络中,提...研究了基于多级Clos数据中心网络的光电交换架构下的流量调度算法,以减少数据传输时延,同时也保证无丢包。传统ADAPT调度算法能实现加速比最小化,但仍然有一些空闲时间槽,而造成带宽未被充分利用。为了解决该问题,在多级Clos网络中,提出了一个多跳路由和调度(Multi-Hop Routing and Scheduling,MHRS)算法,该算法可以在不增加加速比的同时充分利用空闲的带宽。与ADAPT算法类似,MHRS算法先将流量矩阵分解为商矩阵和余矩阵,然后实现两步调度,即将单跳作为第一步,将多跳作为第二步。第一步将余矩阵中的一些数据包调度到商矩阵所形成的配置矩阵的空闲时间槽中,而当这些数据包不能在第一步中被直接调度时,则采用第二步绕道的多跳调度过程传输数据包。仿真结果证明,在多级Clos网络中MHRS算法比ADAPT算法性能更好。展开更多
基金Supported by the National Natural Science Foun-dation of China (60573089) the National 985 Project Fundation(985-2-DB-Y01)
文摘How to process aggregate queries over data streams efficiently and effectively have been becoming hot re search topics in both academic community and industrial community. Aiming at the issues, a novel Linked-tree algorithm based on sliding window is proposed in this paper. Due to the proposal of concept area, the Linked-tree algorithm reuses many primary results in last window and then avoids lots of unnecessary repeated comparison operations between two successive windows. As a result, execution efficiency of MAX query is improved dramatically. In addition, since the size of memory is relevant to the number of areas but irrelevant to the size of sliding window, memory is economized greatly. The extensive experimental results show that the performance of Linked-tree algorithm has significant improvement gains over the traditional SC （Simple Compared） algorithm and Ranked-tree algorithm.
文摘Vehicular ad hoc networks(VANETs)support safety-and non-safety-related applications that require the transmission of emergency safety messages and periodic beacon messages.The dedicated short-range communication(DSRC)standard in VANETs is used to exchange safety messages,and is involved in multi-hop data dissemination and routing.Many researchers have focused either on emergency data dissemination or routing,but both are critical.Routing protocols are commonly used for position-based routing and distancebased routing.This paper focuses on both emergency data dissemination and multi-hop routing,with the selection of the best data disseminator and trustworthy forwarder.To select the best forwarder,ring partitioning is performed,which segregates vehicles into rings based on the coverage area for routing.Each partition is selected with a best forwarder,which minimizes the hop count for data transmission.The work also includes effective video transmission for a user’s request.Video transmission in VANETs is involved in this work to provide efficient video delivery between rapidly travelling vehicles with reduced delay owing to the selection of good-quality channels.Video transmission is prioritized according to frame types,and they are then transmitted with respect to the preference of channels.The major issue in video streaming is the loss of packets,which is our focus to minimize it.Our proposed VANET environment is simulated in OMNeT++,and the results show remarkable improvements in terms of the packet delivery ratio,end-to-end delay,and reliability.
文摘研究了基于多级Clos数据中心网络的光电交换架构下的流量调度算法,以减少数据传输时延,同时也保证无丢包。传统ADAPT调度算法能实现加速比最小化,但仍然有一些空闲时间槽,而造成带宽未被充分利用。为了解决该问题,在多级Clos网络中,提出了一个多跳路由和调度(Multi-Hop Routing and Scheduling,MHRS)算法,该算法可以在不增加加速比的同时充分利用空闲的带宽。与ADAPT算法类似,MHRS算法先将流量矩阵分解为商矩阵和余矩阵,然后实现两步调度,即将单跳作为第一步,将多跳作为第二步。第一步将余矩阵中的一些数据包调度到商矩阵所形成的配置矩阵的空闲时间槽中,而当这些数据包不能在第一步中被直接调度时,则采用第二步绕道的多跳调度过程传输数据包。仿真结果证明,在多级Clos网络中MHRS算法比ADAPT算法性能更好。
