선박 네트워크에서 스마트 장치간 연결성 향상을 위한 릴레이 통신 기법

We study the degradation in network performance caused by the selfish behavior of noncooperative network users. We consider a directed network in which each edge possesses a latency function describing the common latency incurred by all traffic on the edge as a function of the edge congestion. Given a rate of traffic between each pair of nodes in the network, we aspire toward an assignment of traffic to paths in which the sum of all travel times (the total latency) is minimized; however, in many settings network users are free to route their traffic in a selfish manner, without regard to the total latency. We therefore assume that each network user routes its traffic on the minimum-latency path available to it, given the network congestion caused by the other users. In general such a selfishly motivated assignment of traffic to paths (a Nash equilibrium) will not minimize the total latency; hence, selfish behavior carries the cost of decreased network performance. We quantify this degradation in network performance via the price of anarchy, defined as the worst possible ratio between the total latency of a Nash equilibrium and of a minimum-latency routing of the traffic.In this paper, we show that the underlying network topology plays no role in the determination of the price of anarchy. Specifically, we show that under weak hypotheses on the class of allowable edge latency functions, the worst-case ratio between the total latency of a Nash equilibrium and of a minimum-latency routing for any multicommodity flow network is achieved by a single-commodity instance on a set of parallel links. In the special case where the class of allowable latency functions includes all of the constant functions, we prove that a network with only two parallel links suffices to achieve the worst-possible ratio. Informally, these results imply that the inefficiency inherent in a flow at Nash equilibrium stems from the inability of selfish users to discern which of two competing routes is superior and not from the topological complexity arising from the diverse intersections of many paths belonging to different commoditie.Our proof techniques also give powerful methods for computing the price of anarchy with respect to an arbitrary class of latency functions. We apply these methods to function classes that have been well studied in the literature (such as degree-bounded polynomials and functions of the form $\ell(x) = (u—x)—1} that are used to model edges with capacity u), thereby achieving the first tight analyses of the price of anarchy for significant classes of latency functions outside the class of linear functions.

Robust PMU Placement in Branch Switching Power Networks for Minimum Variance State Estimation

Routing in Vehicular Ad hoc Networks (VANET) is a bit complicated because of the nature of the high dynamic mobility. The efficiency of routing protocol is influenced by a number of factors such as network density, bandwidth constraints, traffic load, and mobility patterns resulting in frequency changes in network topology. Therefore, Quality of Service (QoS) is strongly needed to enhance the capability of the routing protocol and improve the overall network performance. In this paper, we introduce a statistical framework model to address the problem of optimizing routing configuration parameters in Vehicle-to-Vehicle (V2V) communication. Our framework solution is based on the utilization of the network resources to further reflect the current state of the network and to balance the trade-off between frequent changes in network topology and the QoS requirements. It consists of three stages: simulation network stage used to execute different urban scenarios, the function stage used as a competitive approach to aggregate the weighted cost of the factors in a single value, and optimization stage used to evaluate the communication cost and to obtain the optimal configuration based on the competitive cost. The simulation results show significant performance improvement in terms of the Packet Delivery Ratio (PDR), Normalized Routing Load (NRL), Packet loss (PL), and End-to-End Delay (E2ED).

In this paper, we combined Self-Organizing Time Division Multiple Access (SOTDMA) and software defined wireless network (SDWN) to apply in the next generation ship area network (SAN). We introduced network controller policy and resource pool to reduce network delay and achieve high performance. We sketch out changes and extensions to controller platforms, and wireless AP stations to enable software defined wireless networks. The complete design of a SDWN architecture using SOTDMA is an exciting avenue for future ship area network. Our evaluation result shows that for one wireless AP station can obtain the expected 3 Mbps throughput.

Critical node discovery plays a vital role in assessing the vulnerability of a computer network to malicious attacks and failures and provides a useful tool with which one can greatly improve network security and reliability. In this paper, we propose a new metric to characterize the criticality of a node in an arbitrary computer network which we refer to as the Combined Banzhaf & Diversity Index (CBDI). The metric utilizes a diversity index which is based on the variability of a node׳s attributes relative to its neighbours and the Banzhaf power index which characterizes the degree of participation of a node in forming shortest paths. The Banzhaf power index is inspired from the theory of voting games in game theory. The proposed metric is evaluated using analysis and simulations. The criticality of nodes in a network is assessed based on the degradation in network performance achieved when these nodes are removed. We use several performance metrics to evaluate network performance including the algebraic connectivity which is a spectral metric characterizing the connectivity robustness of the network. Extensive simulations in a number of network topologies indicate that the proposed CBDI index chooses more critical nodes which, when removed, degrade network performance to a greater extent than if critical nodes based on other criticality metrics were removed.

Over current relay coordination in a meshed distribution system with multiple distributed renewable energy sources (RES) is a very challenging for the protection engineers. The exiting over current relays in the distribution system is set for some predefined network topology and fault currents. Connection of RES results change in network topology and causes additional fault current contribution from these power sources in the distribution systems. The contribution of fault currents from incoming RESs under changed network topology results in mal-operation of over current relays. Modifications of the existing over current relay settings for each new incoming RES is not practically feasible in field. Fault current limiters (FCL) have the capability to block the fault current under fault duration and offers very low resistance to the normal load currents in the distribution systems. This feature of FCL is utilized in this article to restore the over current relay coordination in the distribution system under RES penetration. These FCL devices will eliminate the impact of fault currents on the exiting over current relay coordination in the distribution systems. So, this is a non-adaptive type of over current relay coordination protection scheme, in which the settings of over current relay are not changes as per the injection of RES. The proposed non-adaptive over current relay coordination approaches is implemented in 33 KV distribution side of for IEEE 30 bus system.

Due to the dynamic change of the opportunistic network topology and the lack of stable information transmission paths between nodes, the traditional topology-based routing algorithm cannot achieve the desired routing performance. To address of this problem, this paper proposes a routing algorithm based on trajectory prediction (RATP). The routing protocol based on trajectory prediction can efficiently and quickly adapt to the network link quality instability and the dynamic changes of network topology. RATP algorithm constructs a node mobility model by analyzing the historical mobility characteristics of the nodes. According to the node prediction information, the metric value of the candidate node is calculated, and the node with the smaller metric value is selected as the data forwarding node, which can effectively reduce the packet loss rate and avoids excessive consumption. Simulation results show that compared with other algorithms, the proposed algorithm has higher data delivery ratio, and end-to-end data delay and routing overhead are significantly reduced.

Wireless Ad Hoc network routing algorithm is one of the core technologies of wireless Ad Hoc networks. Ad Hoc network is dynamic topology on characteristic, mainly reflected on the network node number and node movement, which lead to network topology changes, in order to study the Ad Hoc network size and topology changes influence on packet delivery, time delay and routing control, through experiment it is concluded that, the dynamic source routing protocol is an ideal choice.

Over the past few years, a large number of mobile devices are being used in real life with the advancement of wireless technology. The explosive increase in the number of wireless mobile devices makes it impossible to avoid the co-channel interference (CCI) or adjacent channel interference (ACI) phenomenon. Therefore, this interference phenomenon has been recognized as an important problem as it causes network performance degradation. In this paper, we conducted a CCI experiment in an outdoor environment where a Wi-Fi signal is not detected and in the ns-3 simulator, and compared the CCI phenomenon with the experiment results and simulation results. As we evaluated network performance between real network and simulation, we analyzed the performance impact at each network stack how packet errors propagate to upper layers in wireless ad-hoc network and propose a theoretical maximum throughput considering error rate in the data link layer and TCP layer.

Mobile Ad hoc Network (MANET) basically, is a collection of mobile hosts incorporating wireless interfaces that forms a transitory autonomous network. They do not base on fixed infrastructure or central administration, rather work on the principle of self-organized interconnections among mobile nodes. Fundamentally, in MANET when nodes come inside the transmission range of neighboring nodes', they can be detected by each other and can communicate directly. However for communication outside this range they have to depend on some other nodes to relay the messages .This is where routing protocols have to play a very important role. Literature for improving the performance of routing protocol is available in abundance. Among these comes, the hierarchical/cluster-based routing protocols that claim to reduce control overheads. Clustering in Mobile Ad hoc Networks (MANETs) has proved to be advantageous compared to the traditional networks. However the highly dynamic and unstable nature of MANETs makes it intricate for the cluster based routing protocols to split a mobile network into clusters and determination of cluster heads for each cluster. Although much previous research has concentrated on cluster-head selection in MANETs, not much effort has been done on the security side of cluster-head selection. This paper emphasize that secure cluster head selection in MANETs has an intense effect on network performance. Specifically, we stress that in ad hoc network where all the participants are self controlled, security is an essential aspect and the effective cluster-head selection can improve network throughput. We propose a secure and effective cluster-head Selection scheme using a cross-layer approach that integrates cluster-head discovery and selection functionality with network ad hoc routing mechanisms and the lower layer drivers built-in the system. Besides, proposed scheme handle the disconnections in ad hoc network due to the effects of topology changes and battery depletion. This scheme allows clients to switch to better cluster-head nodes as network topology changes. Hence, provides better performance to network.

When a service is offered by multiple servers in a mobile ad hoc network (MANETs), the manner in which clients and servers are paired together, referred to as service selection, is crucial to network performance. Good service selection groups clients with nearby servers, localizing communication, which in turn reduces inter-node interference and allows for multiple concurrent transmissions in different parts of the network. Although much previous research has concentrated on service discovery in MANETs, not much effort has gone into understanding the effects of service selection. This paper demonstrates that service selection in MANETs has profound implications for network performance. Specifically, we show that effective service selection can improve network throughput by up to 400%. We show that to maximize performance service selection decisions need to be continuously reassessed to offset the effects of topology changes. We argue that effective service selection in MANETs requires a cross-layer approach that integrates service discovery and selection functionality with network ad hoc routing mechanisms. The cross-layer approach leverages existing routing traffic and allows clients to switch to better servers as network topology changes

Wireless sensor networks are widely applied in various applications. But due to the resource-constrained sensor nodes and the malicious attacks, the traditional key management schemes are not suitable for the network. Based on the particularities, many relevant key management schemes are developed for wireless sensor networks. This paper proposes an improved matrix key-distribution scheme for wireless sensor networks. This scheme can delete and update key information with the network topology changes to avoid key information to be revealed. Also, base on the clustered structure, this scheme can reduce communication, computation and key storage overhead, which can solve the problem that each sensor node has limited resource. Comparison and simulation results show that the proposed scheme can perform better than most of the existing key management schemes in the network security, key storage overhead.

Quantifying the resilience of community structures in networks

This paper presents the design, implementation and evaluation of Limiting Greedy Connections (LGC), an active mechanism for controlling unresponsive connections and minimizing the degradation in network performance caused by bandwidth‐greedy applications. The primary objectives of the LGC mechanism are to limit the impact of greedy connections on a congested node, to keep a loose upper bound on the packet queue occupancy at the intermediate nodes of the network and to minimize packet loss. The LGC mechanism is evaluated for a variety of network topologies, transmitting sources and node queue parameters, using a Java‐based active network testbed. Copyright © 2003 John Wiley &Sons, Ltd.

Due to the high mobility and dynamic topology of the FANET network, maintaining communication links between UAVs is a challenging task. The topology of these networks is more dynamic than traditional mobile networks, which raises challenges for the routing protocol. The existing routing protocols for these networks partly fail to detect network topology changes. Few methods have recently been proposed to overcome this problem due to the rapid changes of network topology. We try to solve this problem by designing a new dynamic routing method for a group of UAVs using Hybrid SDN technology (SDN and a distributed routing protocol) with a highly dynamic topology. Comparison of the proposed method performance and two other algorithms is simulated. The simulation results show that the proposed method has better results than traditional algorithms in the package delivery ratio, average end to end delay, packet loss, throughput and normalized routing Load.