Hiroyuki Ebara

A Broadcasting Algorithm with Time and Message Optimum on Arrangement Graphs

In this paper, we propose a distributed broadcasting algorithm with optimal time complexity and without message redundancy for one-toall broadcasting in the one-port communication model on arrangement graph interconnection networks. The algorithm exploits the hierarchical property of the arrangement graph to construct dierent-sized broadcasting trees for dierent-sized subgraphs. These dierent-sized broadcasting trees constitute a spanning tree on the arrangement graph. Every processor individually performs its broadcasting procedure based on the spanning tree. It is shown that a message can be broadcast to all the other n! (n k)! 1 processors in at most O(k lgn) steps on the (n;k)-arrangement graph interconnection network. The algorithm can also guarantee that each of processors on the arrangement graph interconnection network receives the message exactly once.

File allocation in distributed multimedia information networks

We study allocation problems of multimedia files in distributed network systems. In these systems, the files are shared by users connected with different servers through high-speed communication networks. One of the most important problems in distributed systems is how to assign the files to servers in view of costs and delays. In these systems, it is obvious that there is a trading-off relationship between costs and delays. Our objective is to find the optimal file allocation such that the total cost is minimized subject to the total delay. In order to evaluate the optimization, we present a system model that can cover a wide range of multimedia network applications such as VoD (video on demand), corporation information networks, and so on. We introduce a 0-1 integer programming formulation for the optimization problem. We find the optimal file allocation by solving these formulae, and quantify the general tendency in distributed systems. Moreover, we make a comparison between the exhaustive search and the approximate method that we use for optimization.

A Cost-Effective Dynamic Content Migration Method in CDNs

Content Distribution Networks (CDNs) are highly advanced architectures for networks on the Internet, providing low latency, scalability, fault tolerance, and load balancing. One of the most important issues to realize these advantages of CDNs is dynamic content allocation to deal with temporal load fluctuation, which provides mirroring of content files in order to distribute user accesses. Since user accesses for content files change over time, the content files need to be reallocated appropriately. In this paper, we propose a cost-effective content migration method called the Step-by-Step (SxS) Migration Algorithm for CDNs, which can dynamically relocate content files while reducing transmission cost. We show that our method maintains sufficient performance while reducing cost in comparison to the conventional shortest-path migration method. Furthermore, we present six life cycle models of content to consider realistic traffic patterns in our simulation experiments. Finally, we evaluate the effectiveness of our SxS Migration Algorithm for dynamic content reconfiguration across time.

Fault-Tolerant Broadcasting on the Arrangement Graph

This paper proposes a distributed fault-tolerant algorithm for one-to-all broadcasting in the one-port communication model on the arrangement graph. Exploiting the hierarchical properties of the arrangement graph to constitute different-sized broadcasting trees for different-sized subgraphs, we propose a distributed algorithm with optimal time complexity and without message redundancy for one-to-all broadcasting in the one-port communication model for the fault-free arrangement graph. According to the property that there is a family of k(n - k) node-disjoint paths between any two nodes, we develop a fast fault-tolerant procedure capable of sending a message from a node to its adjacent nodes on the (n, k)-arrangement graph with less than k(n - k) faulty edges. Combining the fault-tolerant procedure and the optimal broadcasting algorithm, a fault-tolerant broadcasting is achieved on the arrangement graph. It is shown that a message can be broadcast to all the other (n!/(n - k)!)- 1 processors in O(k lg n) steps if no faults exist on the (n, k)-arrangement graph, and in O(k 2 lg n + klg 2 n)) steps if the number of faulty edges is less than k(n - k).

Reliability-based optimal allocation of mirror servers for Internet

We consider the optimal mirror allocation problems for the purpose of load balance in network servers. We focus on constructing high-reliability networks, and propose the optimal mirror allocation model such that the system reliability is maximized subject to costs and delays, in view of the trading-off relationship between the reliability and cost. This optimization model is capable of dealing with various kinds of network topology. We formulate this optimization problem as a 0-1 integer programming in this model, and we can find the place where each mirror server should be and the concrete assignment of files to mirror servers. Our objective is to find the optimal mirror allocation by solving this model, and to show the general characteristics about the load balance and the improvement of the system reliability by the distributed mirror allocation, quantitatively.

An efficient adaptive routing algorithm for the faulty star graph

This paper introduces an adaptive distributed routing algorithm for the faulty star graph. By giving two routing rules based on the properties of nodes, an optimal routing function for the fault-free star graph is presented. For a given destination in the n-star graph, n-1 node-disjoint and edge-disjoint subgraphs, which are derived from n-1 adjacent edges of the destination, can be constructed by applying this routing function and the concept of breadth first search. When faults are encountered, the algorithm can route messages to the destination by finding a fault-free subgraph based on the local failure information. As long as the number f of faults (node faults and/or edge faults) is less than the degree n-1 of the n-star graph, the algorithm can adaptively find a path of length at most d+4f to route messages successfully from a source to a destination, where d is the distance between two nodes.

A novel evacuation route search algorithm for route distribution of evacuees groups in fire disasters

A lot of people have suffered and died due to sudden disasters (fire, earthquake, terrorism, etc) in the world. In sudden disasters, it is very important for evacuees to find out appropriate evacuation routes. We previously proposed the evacuation support system named as Emergency Rescue Evacuation Support System (ERESS). This system is based on MANET and aims to dramatically reduce the number of victims in sudden disasters. This paper deals with the evacuation route search which is one of the most important functions of ERESS. In this paper, we propose a new evacuation route search algorithm for route distribution of evacuees groups in fire disasters. In this algorithm, evacuees can evacuate more safely and immediately by avoiding the congestion passage. To show the validity of the proposed algorithm, we carry out performance evaluations by computer simulations. As the results, we show that more evacuees can evacuate effectively compared with the previous route search algorithm.

Server and route selection method for QoS-based anycast protocol

The anycast communication protocol is to select the best server and the best route for a particular client from a group of replicated servers with the same contents. As users have come to demand contents with high QoS, the necessity to support the anycast communications in QoS networks has grown. In this paper, we propose a server and route selection method with application-level QoS-based anycast protocol. The protocol we propose has the following advantages: 1) the latest server and route information can be constantly acquired through distributed resource management by E-BB; 2) the server and route selection algorithm enable us to consider both the server load and network load simultaneously; and 3) high reliability can be guaranteed by decentralized control.

Near Real-time Mapping Using Shared GPS Data from Stranded Commuters

Japan is known as one of the world’s most quake-prone countries. Many commuters are stranded when major earthquakes occur in Japan. Most of the stranded commuters cannot use mobile devices to connect to the Internet because of the failure of other communication channels. In this paper, we propose sharing GPS data over a DTN (Delay Tolerant Network) to facilitate the generation of near real-time maps and support for stranded commuters in the event of earthquake disasters. To evaluate the network performance, we have carried out simulations using map data for Asahi Ward, Osaka City, in Japan. The results of the simulation indicate that the proposed method achieved the desired accuracy considering reasonable time constraints for near real-time mapping.

An Adaptive Distributed Fault-Tolerant Routing Algorithm for the Star Graph

This paper presents an adaptive distributed fault-tolerant routing algorithm for the n-star graph. Based on the local failure information and the properties of the star graph, the algorithm can make routing decisions without deadlock and livelock. After faults are encountered, the algorithm routes messages to a given destination by finding a fault-free n —1-star graph. As long as the number f of faults (node faults and/or edge faults) is less than the degree n − 1 of the n-star graph, the algorithm can adaptively find a path of length at most d + 6f to route messages from a source to a destination, where d is the distance between tow nodes.