Masahiro Sasabe

Mobile P2P Networks for Highly Dynamic Environments

With the wide spread of mobile devices, information discovery methods over mobile ad hoc networks (MANETs) are required. Recent studies have revealed that integrating a distributed hash table (DHT) substrate and network-layer routing can increase search efficiency. Furthermore, some researchers have proposed a clustering method which groups the overlay nodes according to their physical distance. However, it has also been pointed out that the search efficiency deteriorates in highly dynamic environments. In this paper, we propose a method sharing pointers among nodes in a cluster. Through simulation experiments, we show that the proposed method improves the success ratio of object search up to 40 % compared with existing method.

Scalable and continuous media streaming on peer-to-peer networks

With the growth of computing power and the proliferation of broadband access to the Internet, media streaming has widely diffused. Although the proxy caching technique is one method to accomplish effective media streaming, it cannot adapt to the variations of user locations and diverse user demands. By using the P2P communication architecture, media streaming can be expected to smoothly react to network conditions and changes in user demands for media-streams. We propose efficient methods to achieve continuous and scalable media streaming system. In our mechanisms, a media stream is divided into blocks for efficient use of network bandwidth and storage space. We propose two scalable search methods and two algorithms to determine an optimum provider peer from search results. Through several simulation experiments, we show that the FLS method can perform continuous media play-out while reducing the amount of search traffic to 1/6 compared with full flooding.

LLR: A Construction Scheme of a Low-Diameter, Location-Aware, and Resilient P2P Network

Since a peer searches for its desired file in a P2P file sharing system, the structure of an overlay network determines the effectiveness of search. In this paper, based on the Barabasi-Albert (BA) model, we propose a novel scheme (LLR) to construct a low-diameter and location-aware overlay network where peers can easily find physically-close file holders. LLR has a rewiring method to improve the structure of an overlay network and a recovery method to cope with disappearance of peers. Through several simulation experiments using real physical topologies, we found that LLR could construct an overlay network that had the higher reachability than BA and the higher correlation between physical and logical distances

Evolutionary Game Theory-Based Evaluation of P2P File-Sharing Systems in Heterogeneous Environments

Peer-to-Peer (P2P) file sharing is one of key technologies for achieving attractive P2P multimedia social networking. In P2P file-sharing systems, file availability is improved by cooperative users who cache and share files. Note that file caching carries costs such as storage consumption and processing load. In addition, users have different degrees of cooperativity in file caching and they are in different surrounding environments arising from the topological structure of P2P networks. With evolutionary game theory, this paper evaluates the performance of P2P file sharing systems in such heterogeneous environments. Using micro-macro dynamics, we analyze the impact of the heterogeneity of user selfishness on the file availability and system stability. Further, through simulation experiments with agent-based dynamics, we reveal how other aspects, for example, synchronization among nodes and topological structure, affect the system performance. Both analytical and simulation results show that the environmental heterogeneity contributes to the file availability and system stability.

Media Streaming on P2P Networks with Bio-inspired Cache Replacement Algorithm

With the growth of computing power and the proliferation of broadband access to the Internet, the use of media streaming has become widely diffused. By using the P2P communication architecture, media streaming can be expected to smoothly react to changes in network conditions and user demands for media streams. To achieve continuous and scalable media streaming, we proposed scalable media search and retrieval methods in our previous work. However, through several simulation experiments, we have shown that an LRU (Least Recently Used) cache replacement algorithm cannot provide users with continuous media play-out for unpopular media streams. In this paper, inspired by biological systems, we propose a new algorithm that considers the balance between supply and demand for media streams. Through several simulation experiments, it has been shown that our proposed algorithm could improve the completeness of media play-out compared with LRU.

A Caching Algorithm using Evolutionary Game Theory in a File-Sharing System

In a P2P file-sharing system, a node finds and retrieves its desired file. If multiple nodes cache the same file to provide others, we can achieve a file-sharing system with low latency and high file availability. However, a node has to spend costs, e.g., processing load or storage capacity, on caching of a file. Consequently, a node may selfishly behave and hesitate to cache a file. In such a case, there is a possibility that unpopular files disappear from the system. In this paper, we aim to accomplish effective caching in the whole system that emerges from autonomous and selfish node behavior. We first discuss relationship between selfish node behavior and system dynamics according to evolutionary game theory. As a result, we show that a file-sharing system can be robust to file disappearance depending on a cost and demand model for caching even if nodes behave selfishly.

Effective methods for scalable and continuous media streaming on peer‐to‐peer networks

With the growth of computing power and the proliferation of broadband access to the internet, the use of media streaming has become widely diffused. By using the peer-to-peer (P2P) communication architecture, media streaming can be expected to smoothly react to changes in network conditions and user demands for media streams. In this paper, to achieve continuous and scalable media streaming, we introduce our scalable media search and in-time retrieval methods. Through several simulation experiments, we show that our methods can accomplish continuous media play-out for popular media streams without introducing extra load on the system. However, we also show that an LRU cache replacement algorithm cannot provide users with continuous media play-out for unpopular media streams. To tackle this problem, we take inspiration from biological systems to propose a new cache replacement algorithm that considers the balance between supply and demand for media streams. We demonstrate that our proposed algorithm can improve the continuity of media play-out compared with LRU. Furthermore, we find that the proposed algorithm can adapt to changes in the popularity of various media. Copyright

Automatic evacuation guiding scheme based on implicit interactions between evacuees and their mobile nodes

When large-scale disasters occur, evacuees have to evacuate to safe places quickly. They, however, may not be able to afford to obtain sufficient information for their evacuations under such emergent situations. In this paper, we propose an automatic evacuation guiding scheme using evacuees’ mobile nodes, e.g., smart phones. The key idea to achieve automatic evacuation guiding is implicit interactions between evacuees and their mobile nodes. Each mobile node tries to navigate its evacuee by presenting an evacuation route. At the same time, it can also trace the actual evacuation route of the evacuee as the trajectory by measuring his/her positions periodically. The proposed scheme automatically estimates blocked road segments from the difference between the presented evacuation route and the actual evacuation route, and then recalculates the alternative evacuation route. In addition, evacuees also share such information among them through direct wireless communication with other mobile nodes and that with a server via remaining communication infrastructures. Through simulation experiments, we show that 1) the proposed scheme works well when the degree of damage is high and/or road segments are continuously blocked, 2) the average evacuation time can be improved even in small penetration ratio of the proposed system, and 3) the direct wireless communication can support many evacuations at almost the same level as the communication infrastructure when the number of evacuees becomes large.

Location-aware utility-based routing for store-carry-forward message delivery

One of the most important technical problems in store-carry-forward routing is to reduce the number of message copies in networks without increasing the message delivery delay. In order to solve this problem, we focus on utility-based routing schemes, where for a message, utility of a node indicates its proximity to the destination node of the message. Utility-based routing schemes are promising when relay nodes, i.e., nodes with the message (copy), have sufficient opportunities to encounter other nodes. On the other hand, when relay nodes are in extremely sparse areas of nodes and they have few opportunities to encounter other nodes, the routing schemes do not work effectively. This observation naturally leads us to propose a location-aware utility-based routing scheme. The proposed scheme combines a utility-based routing scheme with location-aware probabilistic forwarding, where the forwarding probability is determined based on both node utility and node density at the contact location. With several simulation scenarios, we evaluate the performance of the proposed scheme in terms of the mean number of copies in the network and the mean message delivery delay.

Automatic Evacuation Guiding Scheme Using Trajectories of Mobile Nodes

When large-scale disasters occur, evacuees have to evacuate to safe places quickly. In this paper, we propose an automatic evacuation guiding scheme using mobile nodes of evacuees. Each node tries to navigate its evacuee by presenting an evacuation route. It can also trace the actual evacuation route of the evacuee as the trajectory by measuring his/her positions periodically. The proposed scheme automatically estimates blocked road segments from the difference between the presented evacuation route and the actual evacuation route, and then recalculates the alternative evacuation route. In addition, evacuees also share such information among them through direct wireless communication with other mobile nodes and that with a server via remaining communication infrastructures. Through simulation experiments, we show that 1) the effectiveness of the proposed scheme becomes high with the increase of degree of damage and 2) the effect of information sharing through communication infrastructures is higher than that through direct wireless communication.