Genya Ishigaki

On Reducing IoT Service Delay via Fog Offloading

With the Internet of Things (IoT) becoming a major component of our daily life, understanding how to improve the quality of service for IoT applications through fog computing is becoming an important problem. In this paper, we introduce a general framework for IoT-fog-cloud applications, and propose a delay-minimizing collaboration and offloading policy for fog-capable devices that aims to reduce the service delay for IoT applications. We then develop an analytical model to evaluate our policy and show how the proposed framework helps to reduce IoT service delay.

Controller placement algorithm to alleviate burdens on communication nodes

This paper proposes an algorithm to determine a controller location on a given network considering burdens of all communication nodes. The burden is defined by extending stress centrality, which indicates a load of each node based on the number of edge disjoint paths. In order to analyze characteristics of the proposed placement algorithm, our simulations compare it with other placement algorithms and the theoretically optimum values in terms of node burdens, latency, survivability and path stability.

On maximizing tree reliability based on minimum diameter spanning tree

For communications networks, reliability is a crucial problem to provide stable services. Hence, this paper defines Maximum Availability Tree (MAT) problem that aims at composing the most reliable tree network in terms of terminal reliability. Our work indicates that MAT problem is converted to Minimum Diameter Spanning Tree (MDST) problem by modeling a network with a probabilistic graph whose edges are assigned probability indicating operability of corresponding communications links. The simulation results demonstrate that MAT improves reliability of communications between any pair of nodes in an obtained network.

Distributed network flow optimization algorithm with tie-set control based on coloring for SDN

This paper proposes a distributed algorithm that aims for congestion control in Software Defined Networking with distributed controllers by exploiting loop structures in a network and coloring. Our algorithm dissects a network into loop units called tie-sets and updates flows on edges by enclosed calculation in each controller, which is in charge of one of loop units. Additionally, the deployment of coloring in a tie-set meta-graph enables the distributed algorithm to avoid update conflicts in shared edges with less communications among controllers.

A tie-set based approach of Software-Defined Networking for traffic load balancing

This paper proposes a traffic Load Balancing (LB) method to alleviate load concentrations on links for large-scale networks. In this paper, the traffic LB problem is formulated in a graph with unsplittable multi-commodity flows which have fixed attributes and pairs of source and destination. The proposed method calculates combinations of routes that minimize the load factor for each ring structures on a network. Balancing of link load factor in a whole network is achieved by repeating the process of minimization method for each ring structure. Our simulation results show that this method is more effective for larger graphs in terms of the balancing performance. The convergence of this algorithm is also demonstrated empirically.

Multi-leader Election in a Clustered Graph for Distributed Network Control

This paper discusses an election problem of multiple leaders in a network divided into clusters which specifically takes a form of ring structures or cycles. The objective function is defined by considering a positional relation between adjacent leaders aiming at the reduction of communication latency in a distributed network control. We propose several heuristic approaches which can be adopted to solve the optimization problem in a polynomial time. Our simulations verify the effectiveness of the obtained solutions in different types of graph models.

On composing a resilient tree in a network with intermittent links based on stress centrality

This paper discusses a composition problem of a resilient tree on a graph modeling a communication network whose links are intermittent. The resiliency of a tree is defined exploiting the binary relation on two kinds of edge weights: availability and commonality. Availability represents a probabilistic stability of a communication link corresponding to an edge, and commonality indicates the influence of an edge based on relative locations of edges on a tree. Our simulation analyzes that the trees satisfying the proposed ordering property on the binary relation provide more stable connections among communication nodes.

Significance Analysis for Edges in a Graph by means of Leveling Variables on Nodes

This paper proposes a novel measure for edge significance considering quantity propagation in a graph. Our method utilizes a pseudo propagation process brought by solving a problem of a load balancing on nodes. Edge significance is defined as a difference of propagation in a graph with an edge to without it. The simulation compares our proposed method with the traditional betweenness centrality in order to obtain differences of our measure to a type of centrality, which considers propagation process in a graph.