共查询到20条相似文献,搜索用时 31 毫秒
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The general problem of estimating origin-destination matrices in congested traffic networks is formulated as a mathematical program with equilibrium constraints. In this paper a path flow entropy model based on an equilibrium assignment approach is presented. It is assumed the flows on links are disaggregated due to some external reasons. Using the L-shaped algorithm the problem is transformed into a problem with less constraints. Then applying the lagrangian dual function the original problem is reduced to a nonlinear convex problem with only one linear constraint. 相似文献
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考虑信道频宽对链路传输距离和链路间干扰的影响,对可变频宽无线网络现有的累积干扰模型进行了改进,并基于改进的干扰模型对可变频宽无线网络的信道频谱分配和链路调度问题进行了建模分析。设计了一种两层优化算法对信道频谱分配和链路调度问题进行解耦,提出了一种考虑链路负载需求满足程度的链路优先级指标,启发式地构建并发传输信道分配矩阵的方法。仿真结果表明,两层优化算法能够在合理时间内收敛,启发式方法能够高效地构建并发传输信道分配矩阵。 相似文献
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Our study is motivated by the need to enable quality of service (QoS), congestion control and fair rate allocation for all end applications. We propose a new approach to address these needs which is different from the current practice whereby end applications pursue their own rate control using TCP. Our approach comprises a network rate management protocol (RMP) that controls the rate of all flows (at an aggregate level based on routes) subject to QoS requirements. The RMP control also facilitates a new TCP sliding-window congestion control based on the fair target rates computed by the RMP. Each non-TCP aggregate flow is policed by its respective edge router and each TCP flow adapts its window size as to achieve the RMP suggested fair target rate. The stability analysis of the new TCP congestion control is performed in a linearly scalable framework, which is less restrictive than a fluid model. We show that our proposed control is linearly scalable and establish its global asymptotic stability under arbitrary and variable information time lags, aka totally asynchronous conditions. The stability and the vitality of our control is verified by two means. One is a simulation of a network comprising 74 core links and up to 768 flows, each using its own access link. The simulation is also used to compare our control with the congestion control algorithms used in Fast, Vegas and Reno TCPs. The second verification means is an actual implementation of the control in the Linux kernel and its experimentation in a WAN testbed network comprising six routers and long haul links running UDP flows as well as CUBIC, N-RENO and C-TCP flows. Our experiments demonstrate that our approach can guarantee fair rates for all flows and QoS to premium flows. 相似文献
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软件定义网络架构下基于流调度代价的数据中心网络拥塞控制路由算法 总被引:1,自引:0,他引:1
针对传统数据中心网络极易发生拥塞的问题,提出了在软件定义网络(SDN)的架构下设计基于流调度代价的拥塞控制路由算法加以解决。首先,进行拥塞链路上的大小流区分,并对所有大流的各条等价路径进行路径开销权重的计算,选择权重最小的路径作为可用调度路径;然后,使用调度后路径开销变化量和流占用带宽比例来共同定义流调度代价;最终选择调度代价最小的流进行调度。仿真结果表明,所提算法能在网络发生拥塞时降低了拥塞链路上的负荷,并且与仅进行流路径选择的拥塞控制算法相比,提高了链路利用率,减少了流传输时间,使得网络链路资源得到更好的利用。 相似文献
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随着数据中心内的数据流量不断增加,导致网络中部分链路负载过重。传统的ECMP机制由于没有考虑链路状态以及流量特征,因此不再适用数据中心网络。同时ECMP可能会将多条大流映射到同一条路径上,造成大流映射冲突,导致链路瓶颈问题。基于SDN(Software Defined Network)架构提出一种面向Fat-Tree拓扑的动态流量负载均衡机制(Load Balancing based on Flow Classification,LBFC),同时考虑了链路状态信息与流量特征进行负载均衡。LBFC机制动态调整流分类阈值来判定大流和小流,采用不同的方式为大流和小流选择转发路径,以满足大流和小流不同的传输性能需求。仿真结果表明LBFC机制能够根据网络链路状态以及流量特征动态地判定大流和小流并实现负载均衡,与ECMP、GFF和DLB算法相比,LBFC机制提高了网络吞吐量以及链路利用率,降低了传输时延。 相似文献
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Traffic network models tend to become very large even for medium-size static assignment problems. Adding a time dimension, together with time-varying flows and travel times within links and queues, greatly increases the scale and complexity of the problem. In view of this, to retain tractability in dynamic traffic assignment (DTA) formulations, especially in mathematical programming formulations, additional assumptions are normally introduced. In particular, the time varying flows and travel times within links are formulated as so-called whole-link models. We consider the most commonly used of these whole-link models and some of their limitations.In current whole-link travel-time models, a vehicle's travel time on a link is treated as a function only of the number of vehicles on the link at the moment the vehicle enters. We first relax this by letting a vehicle's travel time depend on the inflow rate when it enters and the outflow rate when it exits. We further relax the dynamic assignment formulation by stating it as a bi-level program, consisting of a network model and a set of link travel time sub-models, one for each link. The former (the network model) takes the link travel times as bounded and assigns flows to links and routes. The latter (the set of link models) does the reverse, that is, takes link inflows as given and finds bounds on link travel times. We solve this combined model by iterating between the network model and link sub-models until a consistent solution is found. This decomposition allows a much wider range of link flow or travel time models to be used. In particular, the link travel time models need not be whole-link models and can be detailed models of flow, speed and density varying along the link. In our numerical examples, algorithms designed to solve this bi-level program converged quickly, but much remains to be done in exploring this approach further. The algorithms for solving the bi-level formulation may be interpreted as traveller learning behaviour, hence as a day-to-day traffic dynamics. Thus, even though in our experiments the algorithms always converged, their behaviour is still of interest even if they cycled rather than converged. Directions for further research are noted. The bi-level model can be extended to handle issues and features similar to those addressed by other DTA models. 相似文献
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This technical note focuses on the link flow uniqueness of user equilibrium (UE) with speed limits. Under a mild assumption on the monotonicity of link travel time function, the UE link flow solutions are well recognized to be unique. However, the incorporation of speed limits in the network has undermined the strict monotonicity of link travel time functions, thus the UE flows on the links with speed limits may not be unique. This note addresses the uniqueness problem with two major contributions. First, a polyhedron defined on links is provided, and it is proven that the UE link flow is unique if and only if the polyhedron only contains one value. Second, two concise methods are proposed to mathematically check whether the polyhedron is a singleton, which can be easily solved and convenient for practical use. 相似文献
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This paper proposes a new approach to image-based rendering that generates an image viewed from an arbitrary camera position and orientation by rendering optical flows extracted from reference images. To derive valid optical flows, we develop an analysis technique that improves the quality of stereo matching. Without using any special equipments such as range cameras, this technique constructs reliable optical flows from a sequence of matching results between reference images. We also derive validity conditions of optical flows and show that the obtained flows satisfy those conditions. Since environment geometry is inferred from the optical flows, we are able to generate more accurate images with this additional geometric information. Our approach makes it possible to combine an image rendered from optical flows with an image generated by a conventional rendering technique through a simple Z-buffer algorithm. 相似文献
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Yongjun Li Wandong Cai 《通讯和计算机》2006,3(3):19-24
A simple bottom-up loss inference approach is proposed in reference [1], which infers the link loss rate from the multicast in the end-to-end measurements. However, the spatial independence is assumed in the loss model. In fact the spatial dependence is present in packet losses, so the loss model assumption is violated. Moreover, with this approach, it is difficult to identify all the cuts of a multi-level tree, which is used to estimate the network-internal link loss rate. To overcome these shortcomings, an improved approach is proposed in this paper. In the proposed approach, the virtual link is employed to infer the network-internal link loss performance without using the concept cuts and the spatial dependence between the links is taken into account. Simulation results show that the inferred results correctly show the loss trend of the links. The proposed approach can also be extended to be the general tree topology. 相似文献
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基于链接分块的相关链接提取方法 总被引:1,自引:0,他引:1
每个网页都包含了大量的超链接,其中既包含了相关链接,也包含了大量噪声链接。提出了一种基于链接分块的相关链接提取方法。首先,将网页按照HTML语言中标签将网页分成许多的块,从块中提取链接,形成若干链接块;其次,根据相关链接的成块出现,相关链接文字与其所在网页标题含相同词等特征,应用规则与统计相结合的方法从所有链接块中提取相关链接块。相关链接提取方法测试结果,精确率在85%以上,召回率在70%左右,表明该方法很有效。 相似文献