Chisa Takano

Stability and adaptability of autonomous decentralized flow control in high-speed networks

This paper focuses on flow control in high-speed networks. Each node in a network handles its local traffic flow only on the basis of the information it is aware of, but it is preferable that the decision-making of each node leads to high performance of the whole network. To this end, we investigate the relationship between the flow control mechanism of each node and network performance. We consider the situation in which the capacity of a link in the network is changed but individual nodes are not aware of this. Then we investigate the stability and adaptability of the network performance when the capacity of a link is changed, and discuss an appropriate flow control model on the basis of simulation results.

Diffusion-Type Autonomous Decentralized Flow Control for End-to-End Flow in High-Speed Networks

SUMMARY We have proposed diffusion-type flow control as a solution for the extremely time-sensitive flow control required for high-speed networks. In our method of flow control, we design in advance simple and appropriate rules for action at the nodes, and these automatically result in stable and efficient network-wide performance through local interactions between nodes. Specifically, we design the rules for the flow control action of each node that simulates the local interaction of a diffusion phenomenon, in order that the packet density is diffused throughout the network as soon as possible. However, in order to make a comparison with other flow control methods under the same conditions, the evaluations in our previous studies used a closed network model, in which the number of packets was unchanged. This paper investigates the performance of our flow control method for an end-to-end flow, in order to show that it is still effective in more realistic networks. We identify the key issues associated with our flow control method when applied to an open network model, and demonstrate a two-step solution. First, we consider the rule for flow control action at the boundary node, which is the ingress node in the network, and propose a rule to achieve smooth diffusion of the packet density. Secondly, we introduce a shaping mechanism, which keeps the number of packets in the

Diffusion-Type Autonomous Decentralized Flow Control for Multiple Flows

SUMMARY We have proposed a diffusion-type flow control mechanism to achieve the extremely time-sensitive flow control required for highspeed networks. In this mechanism, each node in a network manages its local traffic flow only on the basis of the local information directly available to it, by using predetermined rules. In this way, the implementation of decision-making at each node can lead to optimal performance for the whole network. Our previous studies concentrated on the flow control for a single flow. In this paper, we propose a diffusion-type flow control mechanism for multiple flows. The proposed scheme enables a network to quickly

Autonomous Decentralized Mechanism of Structure Formation Adapting to Network Conditions

We have already proposed the framework of autonomous decentralized control based on local-interaction as a novel control mechanism for communication networks. This framework is based on the relation between local interaction and the solution yielded by a partial differential equation. In this framework, the behavior of the whole system is indirectly controlled by appropriately designing the autonomous operation of the subsystems. That is, the local action rules (micro-level) are designed to produce an appropriate state of the whole system at the macro-level. In previous studies, we proposed flow control based on a diffusion equation to realize autonomous congestion avoidance in networks. This paper proposes a new autonomous decentralized structure forming method based on our framework. First, we introduce the renormalization transformation of the diffusion phenomenon for a one-dimensional network model and propose autonomous decentralized forming of a structure that has finite spatial size. In addition, to apply this method to a general network topology, we first extend the one-dimensional network model to a n-dimensional Euclid space and derive the control rule that can be applied to a general network by using the discretization method. As an application example, we demonstrate the autonomous decentralized clustering of a sensor network for a two-dimensional lattice network model and show the characteristics of the proposed method in this application.

Cluster structures in topology of large-scale social networks revealed by traffic data

Many studies of social networks have recently been published. Interest in topological structures, such as scale-free characteristics, has been particularly strong. In this paper, we focus on the analysis of macro traffic data in a communications network of cellular phone users as a way of investigating large-scale social networks. Behaviors of information exchange between pairs of cellular phone users are reflected in traffic data, which thus reflects interesting features of social networks. We analyze the relationship between the number of customers and the volume of traffic with a view to finding clues about the structure of social networks among the very large set of potential customers. We then demonstrate some interesting features that our analysis reveals: a scale-free topology of human relations, their cluster structures, and behaviors of user-dynamics. In addition, we consider the relationship between traffic volume and the number of customers depending on the situation.

On Convergence Rate of Autonomous Decentralized Structure Formation Technology for Clustering in Ad Hoc Networks

Hierarchization by clustering is effective for scalable routing control in an ad hoc network. Due to a constraint from structural features of ad hoc networks, clustering in ad hoc networks should be autonomous decentralized algorithm based on local information. Bio-inspired approach gives a solution of such autonomous decentralized clustering mechanism and its well-known mechanism is based on reaction-diffusion equations. Apart from this, we have already proposed the autonomous decentralized clustering mechanism for ad hoc networks based on two concepts of renormalization transformation and back-diffusion potential. One of most important requirements to the clustering mechanism is faster convergence speed of clustering to adapt to dynamic environments. In this paper, we compare convergence speed of both mechanisms.

Stability of autonomous decentralized flow control schemes in high-speed networks

Focuses on flow control in high-speed networks. Each node in the networks handles its local traffic flow only on the basis of the information it knows, but it is preferable that the decision-making of each node leads to high performance of the whole network. To this end, we investigated the behavior of packet flow when a node is congested, and show an appropriate flow control model through simulation results.

Proposal of New Index for Describing Node Centralities Based on Oscillation Dynamics on Network

Since recent rapid development of information network technology activates the information exchange on the social network, dynamics for propagation of information or activity on the social network is an interesting research object. The network dynamics is generated by interaction between users whose strength is asymmetric in general. Network structure reflecting the asymmetric interaction between users is modeled by a directed graph, and it is described by an asymmetric matrix in matrix-based network model. In our recent research, we have proposed an oscillation model for describing dynamics on networks generated from a certain kind of asymmetric interaction between nodes by using a symmetric matrix. In this paper, based on the oscillation model, we propose a new extended index of the node centrality. The proposed index can describe various aspect of node centrality that considers not only the topological structure of the network, but also asymmetry of links, the distribution of source node of activity, and temporal evolution of activity propagation.

An access point selection mechanism based on cooperation of access points and users movement

Public areas, such as train stations and airports, providing wireless Local Area Network (WLAN) services are increasing and expanding because of the rapid development of WLANs based on IEEE 802.11 standard. Moreover, because of the advances in smartphone tethering technology, portable access points (APs) such as mobile Wi-Fi routers are being utilized more frequently. Consequently, there are increasing circumstances where a user needs to select and connect to one of the many APs. AP selection significantly determines the quality of service of the subsequent communication session. Existing AP selection algorithms consider user movement but not AP movement. We propose an AP selection method that handles both types of movement effectively. Moreover, we show that the proposed method improves the throughput significantly compared to the existing method.

Setting Radio Transmission Range Using Target Problem to Improve Communication Reachability and Power Saving

Ad hoc networks can be composed entirely of mobile wireless terminals, and do not require permanent network infrastructure such as access points. They are considered a useful network configuration technology for various situations. For example, they are used to construct sensor networks in which distributed, inexpensive sensors monitor environmental conditions such as temperature and humidity. Further, ad hoc networks can be implemented after severe disasters that have disabled other network infrastructures. In general, ad hoc network terminals are battery powered. Therefore, extending network lifetime by reducing terminal power consumption is an important issue in ad hoc network management. One method for reducing power consumption involves reducing the radio transmission range of each terminal. However, reducing the radio transmission range causes degradation in the reachability of each terminal. In this paper, we propose a method to set ad hoc network radio transmission ranges using a Target problem, to reduce power consumption and increase each terminal’s reachability. Next, we evaluate our method using various routing protocols, and define the applicability of our proposed method for each protocol. Simulation results show that the proposal improves communication reachability and power savings in ad hoc networks with normally distributed terminals, when the Destination-Sequenced Distance-Vector (DSDV) routing protocol is used.