Takuya Asaka

Location management using mobile history for hierarchical mobile IPv6 networks

Hierarchical mobile IPv6 (HMIPv6) has been proposed to improve the performance capability of mobile IPv6 at handover. In HMIPv6, local entities named mobility anchor points (MAPs) are distributed throughout a network to localize the management of intra-domain mobility. In this paper, we propose a location management method for hierarchical mobile IPv6 using the mobile nodes (MN) mobile history. In this method, when a MN performs a handover, the access router calculates the area-covered rate of each upper MAP from the MNs mobile history and selects the MAP that best manages the MN in accordance with its rate. Thus, the proposed method reduces both the number of binding updates to the home agent and the signaling traffic. We evaluate the performance of the proposed method by simulation.

Distributed Web caching using hash-based query caching method

Distributed Web caching allows multiple clients to quickly access a pool of popular Web pages. Conventional distributed Web caching schemes, e.g., the Internet cache protocol and hash routing, require the sending of many query messages among cache servers and/or impose a large load on the cache servers when they are widely dispersed. To overcome these problems, we propose a hash-based query caching method using both a hash function and a query caching method. This method can find cached objects among several cache servers by using only one query message. Compared to conventional methods, this method reduces cache server overhead, object retrieval latency and loads to the network.

Multicast routing in satellite-terrestrial networks

Satellite-terrestrial networks, in which many nodes are interconnected by both satellite and terrestrial networks, can efficiently support multicast service. We have developed a dynamic routing algorithm for satellite-terrestrial network that selects the route to use according to the multicast group size when a node is added to the group.

Routing for content oriented networks using dynamic ant colony optimization

Content oriented networks are proposed as a new network architecture that does not rely on an IP address. Content queries are routed on the content name itself instead of a destination address in these content oriented networks. A huge amount of content exists in a network and the contents from mobile devices are also used. When the content from a mobile device moves somewhere else, all the routing tables are generally re-created with the movement information that the mobile device sends. However, a routing scheme that uses ant colony optimization has attracted attention for supporting this process, but there is a problem with this optimization in that it cannot cope with moving contents. In this paper, we propose a scheme that can cope with moving contents by using pheromones that are laid by the moving mobile devices. Moreover, we conducted simulations to evaluate the performance of the proposed scheme.

Event-driven Wireless Sensor Networks using energy-saving data collection

In Wireless Sensor Networks (WSN) nodes are small battery-powered devices and electric power is difficult to supply after the network is activated. Thus, maximizing life time of the network is one of the most important challenges in wireless sensor networks. Also, nodes are allocated at high density because even if some nodes cannot communicate due to breakdown of devices or decrease in battery, network connectivity needs to be maintained. Thus, some nodes that are allocated proximally tend to obtain the same observation information. If a base station node (BS) collects observation information of events from all nodes that detect events, this is not effective from the point of view of power consumption because of communication between some nodes that have the same observation information. This paper proposes a data collecting method that removes redundant communications of observation information for event-driven wireless sensor networks. Our method, which estimates areas of events by communication between nodes and collects events of observation information of only nodes on the edge of the areas, achieves low-energy consumption.

Detection of TCP Performance Degradation Using Link Utilization Statistics

In this paper, we propose a method of detecting TCP performance degradation using only bottleneck-link utilization statistics. The variance of link utilization normally increases as the mean link-utilization increases. However, because link-utilization has a maximum of 100%, as the mean approaches 100%, the variance decreases to zero. In this paper, using the M/G/R processor sharing model, we relate this phenomenon to the behavior of flows. We also show that by using this relationship, we can detect TCP performance degradation using the mean and variance of link utilization. Particularly, with this method, a network operator can determine whether or not the degradation originates from the congestion of his/her own network. Because our method requires us to measure link utilization only, the cost of performance management can be greatly decreased compared with the conventional method, which requires dedicated equipment to measure the network performance.

Power saving mobile sensor networks by relay communications

Mobile sensor networks are attracting a lot of interests. In these networks, nodes not only have sensing capability but mobility as well. Therefore, a few sensor nodes can a cover larger sensing area by moving around. Additionally, dangerous areas where people cannot access, such as disaster sites or radiation-contaminated areas, can be searched by nodes moving around their sensing positions autonomously. A conventional method was proposed to control node movements by using push-based broadcast. However, in the conventional method, nodes cannot move autonomously without broadcast information, and they consume power unequally. We propose a more efficient power reduction scheme that involves relaying data among nodes on rails.

A Hybrid P2P Overlay Network for Non-Strictly Hierarchically Categorized Contents

In P2P content distribution systems, there are many cases in which the content can be classified into hierarchically organized categories. In this paper, we propose a hybrid overlay network design suitable for such content called Pastry/NSHCC (Pastry for non- strictly hierarchically categorized content). The semantic information of classification hierarchies of the content can be utilized regardless of whether they are in a strict tree structure or not. By doing so, the search scope can be restrained to any granularity, and the number of query messages also decreases while maintaining keyword searching available. Through simulation, we showed that the proposed method provides better performance and lower overhead than unstructured overlays exploiting the same semantic information.

A Load Reduction System to Mitigate Flash Crowds on Web Server

In recent years there is a rapid increase of traffic to a given web server within a short time as the number of Internet users increases, and such a phenomenon is called a flash crowd. Once flash crowds occur in the web server, a response rate decreases or the web server may crash as the load increases. We propose a load reduction system, which prevents excessive accesses and stably delivers content without enhancing the performance of the web server even when flash crowds occur. In the proposed system, a proxy server detects flash crowds by monitoring the number of requests and changes a content delivery system. To limit accesses to the web server, the proxy server redirects a request to another client that holds the content in the cache when flash crowds occur. We also propose a content delivery system that uses a tree construction to reduce the client load. Moreover, its efficacy is shown through simulations.

A Hybrid P2P Overlay Network for Non-strictly Hierarchically Categorized Content

In P2P content distribution systems, there are many cases in which the content can be classified into hierarchically organized categories. In this paper, we propose a hybrid overlay network design suitable for such content called Pastry/NSHCC (Pastry for Non-Strictly Hierarchically Categorized Content). The semantic information of classification hierarchies of the content can be utilized regardless of whether they are in a strict tree structure or not. By doing so, the search scope can be restrained to any granularity, and the number of query messages also decreases while maintaining keyword searching availability. Through simulation, we showed that the proposed method provides better performance and lower overhead than unstructured overlays exploiting the same semantic information.