一个低开销的无线传感器网络多径路由协议

针对多对一的周期性数据收集应用,提出一个低开销的逐跳多径路由协议LOMP,综合利用定期和实时估计器评估链路质量,在此基础上实现高质量的多径路由。与现有的多径路由协议相比,LOMP并不提供端到端的节点独立的多径路由,而只是确保在报文的每一跳转发过程中都有多条路径可用。仿真结果表明LOMP能够提高选路质量,以较小的能量开销提高数据传输的可靠性。     

一种改进的软件定义网络低开销一致性更新算法*

针对SDN流表更新一致性、规则空间开销和更新时延问题,提出一种改进的低开销一致性算法。在确保更新过程一致性的前提下,设置基于数据包报头字段和包的位置的谓词,采用线性规划的方法对谓词进行选择排序;优化通过分析对流表项设置优先级的部分,并套用最新的两阶段更新算法进行更新。实验结果表明,与原算法对比,该算法不失其初始功能,并节约3%左右的总更新时间,该算法是一种具有可行性、较快较好的算法。     

Switch cost and packet delay tradeoff in data center networks with switch reconfiguration overhead

Cost minimization is a major concern in data center networks (DCNs). Existing DCNs generally adopt Clos network with crossbar middle switches to achieve non-blocking data switching among the servers, and the number of middle switches is proportional to the number of ports of the aggregation switches in a fixed manner. Besides, reconfiguration overhead of the switches is generally ignored, which may contradict the engineering practice. In this paper, we consider batch scheduling based packet switching in DCNs with reconfiguration overhead at each middle switch, which inevitably leads to packet delay. With existing state-of-the-art traffic matrix decomposition algorithms, we can generate a set of permutations, each of which stands for the configuration of a middle switch. By reconfiguring each middle switch to fulfill multiple configurations in parallel with others, we reveal that a tradeoff exists between packet delay and switch cost (denoted by the number of middle switches), while performance guaranteed switching with bounded packet delay can be achieved without any packet loss. Based on the tradeoff, we can minimize the number of middle switches (under a given packet delay bound) and an overall cost metric (by translating delay into a comparable cost factor), as well as formulating criteria for choosing a proper matrix decomposition algorithm. This provides a flexible way to reduce the number of middle switches by slightly enlarging the packet delay bound.     

Provably secure cloud storage for mobile networks with less computation and smaller overhead

Secure cloud storage (SCS) guarantees the data outsourced to the cloud to remain intact as it was before being outsourced. Previous schemes to ensure cloud storage reliability are either computationally heavy or admitting long overheads, thus are not suitable for mobile networks with strict computation/bandwidth restrictions. In this paper, we build an efficient SCS system for mobile networks based on homomorphic MAC and propose domain extension to enhance the security level and flexibility of the system. In addition, we give a formal security model which is compatible to previous ones and analyze our system in that model. We also give implementations on mobile devices to verify the effectiveness of our system.     

Optimal hop-by-hop flow control in computer networks

The problem of hop-by-hop flow control in a computer network is formulated as a Markov decision process with a cost function composed of the delay of the messages and the buffer constraints. The optimal control is shown to be a linear truncated function of the state and the explicit form is found when the arrival process of the messages is a Bernoulli process. For a renewal arrival process, the long-rnn average cost of any policy with a linear truncated structure is expressed by a set of linear equations.     

Window flow control in computer communication networks

Computer communication networks are basically resource sharing systems and are used for an efficient exchange of information among remote users. Performance (throughput, delay and power) of a computer network depends upon the intensity of data and/or information traffic. If a network's traffic is allowed to increase beyond certain limits, its performance rapidly degrades. In order to keep data traffic under control, some restrictions are applied at various levels of computer communication networks. These restrictions are usually referred to as flow control techniques.

This paper deals with window (also called end-to-end or entry-to-exit) flow control in computer communication networks. In this method, a source node is allowed to have only a limited number of unacknowledged messages, usually termed as “window size”, at a time. Flow control, in this paper, is discussed in the context of three computer communication switching techniques: packet switching, virtual cut-through switching and quasi cut-through switching. The analysis of window flow control is based upon simulation of a typical store-and-forward computer network. Several simulation results are presented to illustrate the effects of window flow control on various computer communication switching techniques.     

Adaptive flow control in high-performance interconnection networks

The flow-control mechanism determinates the manner in which the communicational resources are allocated. Well-designed flow-control mechanism should provide efficient allocation of the communicational resources in wide variety of interconnection networks. The goal of this paper is to suggest a highly effective “Step-Back-on-Blocking” buffered flow control. The proposed flow-control mechanism combines the advantages of the Wormhole and Virtual-Cut Through flow controls, whilst adds a means for adaptive allocation of the communicational resources. The “Step-Back-on-Blocking” flow control provides low message latency and achieves high fraction of the channel bandwidth by performing conditional evasion of temporary blocked network resources. The effectiveness of the proposed flow control has been evaluated on the basis of numerous experiments conducted in OMNet++ discrete event simulation environment.     

网络流驱动的复杂输运网络演化模型

传统复杂网络演化模型在网络拓扑结构与边权演化的机制设计中,未考虑网络流对于输运网络演化的驱动作用。引入网络流的动态驱动机制,分析网络流的规模增长、空间距离的制约与最短路径的配流策略三种因素,在输运网络的演化过程中所发挥的作用。发现这三种因素并不足以改变复杂网络的无标度性;基于最短路径的配流机制是网络流分布不均的关键影响因素;空间距离抑制作用对于网络相配性具有关键影响作用。     

The symbolic algorithms for maximum flow in networks

The maximum flow problem is one of the classic combinatorial optimization problems with many applications, such as electrical powers, traffics, communications, computer networks and logistics. The problem is to find a flow of maximum value on a network from a source to a sink. Ordered binary decision diagram (OBDD) is a canonical form to represent and manipulate the Boolean functions efficiently. OBDD-based symbolic algorithms appear to give improved results for large-scale combinatorial optimization problems by searching the nodes and edges implicitly. For the maximum flow problem in networks, we present the symbolic algebraic decision diagram (ADD) formulation and symbolic algorithms. The augmenting-path-based symbolic algorithm is the combination of the Gabow's scaling algorithm with the binary decision diagram (BDD)-based symbolic algorithm for the maximum flow in 0–1 networks. The Karzanov's algorithm is implemented implicitly, resulting in the preflow-based symbolic algorithm (PSA), in which the vertices on each layer of the layered networks are partitioned by the vertex's input preflow and the total capacity of its outgoing edges, and the edges to push or pull the preflow are selected in terms of the priority function. The improved PSA is developed by integrating the heuristic of Träff's algorithm and the assistant layered networks into the PSA. The symbolic algorithms do not require explicit enumeration of the nodes and edges, and therefore can handle large-scale networks.     

Extra back-off flow control in multi-hop wireless networks

CSMA is the predominant distributed access protocol for wireless mesh networks. Originally designed for single-hop settings, CSMA can exhibit severe performance problems in multi-hop networks in terms of stability and end-to-end throughput. To ensure a smoother flow of packets, we examine an enhancement referred to as Extra Back-off (EB) flow control. In this enhanced scheme a node remains silent for a certain extra back-off time (imposed on top of the usual back-off time that is part of CSMA) after it has transmitted a packet, to give both the downstream and upstream neighbors the opportunity to transmit. EB flow control entails only a small modification to CSMA, preserving its distributed character. In order to examine the performance of EB flow control, we analyze a novel class of Markov models at the interface between classical tandem queues and interacting particle systems. The results demonstrate that EB flow control provides an effective mechanism for improving the end-to-end throughput performance.     

Intelligent material flow by decentralizedcontrol networks

This contribution presents a modular system for decentralized control of track-bound plant-floor material flow. The first main element of the system is a transport network of intelligent track and transport modules that autonomously execute transport orders. There is only a limited number of different standard module types, initially not bound to a specific topology. All modules can independently perform local operations and, in order to coordinate their actions, communicate throughout the network via an integrated data bus. The second pillar is a PC-based graphical user interface for automatically configuring modules with topology data, for passing transport orders to transport modules, and for optionally supervising all concurrent processes.     

A hybrid design-time/run-time scheduling flow to minimise the reconfiguration overhead of FPGAs

Current multimedia applications are characterized by highly dynamic and non-deterministic behaviour as well as high-performance requirements. Potentially, partially reconfigurable fine-grain configurable architectures like FPGAs can be reconfigured at run-time to match the dynamic behaviour. However, the lack of programming support for dynamic task placement as well as the large configuration overhead has prevented their use for highly dynamic applications. To cope with these two problems, we have adopted an FPGA model with specific support for task allocation. On top of this model, we have applied an existing hybrid design-time/run-time scheduling flow initially developed for multiprocessor systems. Finally, we have extended this flow with specific modules that greatly reduce the reconfiguration overhead making it affordable for current multimedia applications.     

无线自组网络QoS流的准入控制和流量控制

作者曾提出一个QoS路由和准入控制机制－QDSR,并且在小规模实时视频传输实验床上实现了这些方案。虽然QDSR的准入控制只保证每个节点有足够的可用带宽给准入的所有流使用,但并不保证每个流在较小的时间尺度上得到请求的带宽。为此,作者对QDSR的准入控制机制进行了改进并增加了流量控制机制,以满足实时应用的QoS需求。在NS2仿真环境中实现了QDSR以及对QDSR的改进。仿真结果表明,改进机制改善了QDSR的视频流的传输质量,较好地提高了视频流的吞吐率和投递率,减小了数据包的端到端延迟,并且能很好地满足包括视频传输在内的多种业务的传输需要。     

Cuckoo search algorithm with membrane communication mechanism for modeling overhead crane systems using RBF neural networks

Developing a precise dynamic model is a critical step in the design and analysis of the overhead crane system. To achieve this objective, we present a novel radial basis function neural network (RBF-NN) modeling method. One challenge for the RBF-NN modeling method is how to determine the RBF-NN parameters reasonably. Although gradient method is widely used to optimize the parameters, it may converge slowly and may not achieve the optimal purpose. Therefore, we propose the cuckoo search algorithm with membrane communication mechanism (mCS) to optimize RBF-NN parameters. In mCS, the membrane communication mechanism is employed to maintain the population diversity and a chaotic local search strategy is adopted to improve the search accuracy. The performance of mCS is confirmed with some benchmark functions. And the analyses on the effect of the communication set size are carried out. Then the mCS is applied to optimize the RBF-NN models for modeling the overhead crane system. The experimental results demonstrate the efficiency and effectiveness of mCS through comparing with that of the standard cuckoo search algorithm (CS) and the gradient method.     

Suitability of different neural networks in daily flow forecasting

Alternative forms of neural networks have been applied to forecast daily river flows on a continuous basis with the purpose of understanding how recent architectures like ANFIS, GRNN and RBF compare with traditional FFBP when monsoon-fed rivers involving significant statistical bias are involved. The forecasts are made at a location called Rajghat along river Narmada in India. Division of yearly data into four seasons and development of separate networks accordingly was found to be more useful than a single network applicable for the entire year. When a variety of error criteria were viewed together the most satisfactory network for all seasons was the radial basis function, which showed better performance then FFBP, GRNN and ANFIS. The FFBP network was found to be equally acceptable as the RBF in seasons other than the monsoon. Generally the peak flows were more satisfactorily modeled by the RBF than FFBP, GRNN and ANFIS. The relatively simpler handling of data non-linearity in FFBP was more attractive than complex ones of ANFIS and GRNN. The representative statistical model, namely response surface method, yielded highly unsatisfactory results compared to any ANN model involved in this study, confirming that the complexity of ANNs is really necessary to model daily river flows.     

The message flow model for routing in wormhole-routed networks

In this paper, we introduce a new approach to deadlock-free routing in wormhole-routed networks called the message flow model. This method may be used to develop deterministic, partially-adaptive, and fully-adaptive routing algorithms for wormhole-routed networks with arbitrary topologies. We first establish the necessary and sufficient condition for deadlock free routing, based on the analysis of the message flow on each channel. We then use the model to develop new adaptive routing algorithms for 2D meshes     

Model-based detection of routing events in discrete flow networks

A theoretical framework and its practical implications for formulating and implementing model-based monitoring of discrete flow networks are discussed. Possible flows of items are described as discrete-event (DE) traces. Each trace defines the DE sequence(s) that are triggered when an entity follows a given flow-path, visiting tracking locations within the monitored system. To deal with alternative routing, creation of items, flow bifurcations and convergences are allowed. Given the set of possible discrete flows, a possible-behavior model—an interacting set of automata—is constructed, where each automation models the item discrete flow at each tracking location. In this model, which assumes total observability, event labels or symbols contain all the information required to unambiguously distinguish each discrete movement. Within the possible behavior, there is a special sub-behavior whose occurrence is required to be detected. The special behavior may be specified by the occurrence of routing events, such as faults or route violations, for example. These intermittent or non-persistent events may occur repeatedly. An observation mask is then defined, characterizing the observation configuration available for collecting item tracking data. The verification task is to determine whether this observation configuration is capable of detecting the specified special behavior. The assessment is accomplished by evaluating several observability notions, such as detectability and diagnosibility. If the corresponding property is satisfied, associated formal observers are constructed to perform the monitoring task at hand. The synthesis of observation masks may also be conducted to suggest optimal observation configurations (specifying number, type, and tracking locations of observation devices) guaranteeing the detection of special events and to construct associated monitoring agents. The developed framework, modeling methodology, and supporting techniques for defining and implementing discrete flow monitoring of entity movements are presented and illustrated with examples.