Toshiya Okabe

Statistical traffic identification method based on flow-level behavior for fair VoIP service

Many threats, such as denial-of-services (DoS) attacks and impersonation, can endanger an IP network where real-time communication, as represented by VoIP, requires a high level of reliability to work as a replacement for PSTN. Without making a concrete framework to protect the reliability of VoIP, we may soon start seeing cases whereby networks are illegally used by impersonating real-time communication. This paper proposes a technique, based on flow-level behavior, which aims to maintain communication confidentiality and identify applications of real-time communication, in a short period of time in order to eliminate applications that illegally use network resources. The paper shows favorable identification results were obtained from our experiments and also introduces issues we have discovered that must be resolved.

Real-time energy exchange strategy of optimally cooperative microgrids for scale-flexible distribution system

Optimal cooperative microgrid formation strategy for minimizing distribution loss (26-80% reduction).The microgrid coalition game is designed and analyzed by Coalitional Game Theory.Scalable for a large number of microgrids and computationally efficient.Applicable to (near) real-time operation due to lower computational and communicative complexity. This paper presents an optimal coalition formation mechanism of microgrids in a smart distribution system and analyzes the characteristics from the coalitional game theoretical perspective. Microgrids coalitions can (1) minimize the energy burden and dependency on the utility grid, (2) minimize the overall grid network power loss, and (3) maximize intra-coalition energy transfer. In order to form cooperative microgrids, a Hierarchical priority based Coalition Scheme (HRCoalition) is proposed. Given an intra-coalition distance threshold, the proposed HRCoalition mechanism can provide the optimal coalition that achieves the aforementioned objectives. The optimality is realized by reaching a state of cooperative equilibrium for all microgrids and coalitions. The optimality of the formed coalitions is proved by Coalitional Game Theory. A Greedy based strategy is designed to perform network constrained energy exchange (GreedEnEx) within a formed coalition. Thus, HRCoalition provides a higher level optimization while, GreedEnEx yields system level optimization using output of HRCoalition. The proposed HRCoalition scheme is computationally very efficient and can scale up to a huge number of microgrids and thus makes it suitable for near real-time operation. An equivalent pricing mechanism is designed to provide a form of economic incentive to the microgrids participating coalition formation. The performance of the proposed method is reported to scale up to 500 microgrids with a loss reduction ranging from 26% to 80%. The provided numerical simulation results back the claim of optimality as well as prove the effectiveness of the proposed coalition formation method.

Wireless LAN access network system for moving vehicles

Several Wireless LAN handover schemes have been proposed for access networks. These efforts have not yet, however, produced a satisfactory solution for access networks that provide broadband Internet services to moving vehicles such as express buses, trucks and high-speed trains. In this paper, we propose a WLAN access network system for high-speed moving vehicles. The proposed system achieves a short handover time and no packet loss during handover. A daisy-chain network architecture reduces construction costs to enable the wide deployment of many WLAN access points. We also present a performance evaluation of the prototype system.

Distributed energy matching and exchange scheme for demand-side optimal operation

This paper introduces a demand-side distributed energy matching framework and operations for an Energy Service Provider (ESP). Due to the diversity, geographical location and high number of customers, managing energy transactions and resulting energy exchanges are challenging for an ESP. The envisioned ESP maintains several aggregators (e.g. Microgrids), named as Sub Service Provider (SSP) that manage customers/subscribers under their domains. The service requires customers to provide pre-committed energy profiles along with preferences over certain attributes on a day-ahead basis. The SSPs (that work under the ESP) act as agents that perform local energy matching within their own domain of customers and distributed energy matching with the colleague SSPs. The goal of the distributed energy matching is to reduce the involvement of utility (in both the day-ahead market and spot-market). In order to perform the distributed matching operation, an assignment problem is designed and solved by Linear Programming. The communicative burden among SSPs due to the exchange of energy information (i.e. to converge in the distributed matching process) is reduced by applying an adaptive microgrid (SSP) coalition formation method.

A Lightweight Application-Layer Signaling Protocol

The session Initiation Protocol (SIP) is a widely used application-layer control protocol. The processing load of the SIP protocol is reportedly seen as one of the potential problems which may limit the range of its application although it has a number of advantages. Many research efforts have been made and have come up with various compression algorithms to reduce the packet size in order not to waste scarce bandwidth especially for wireless access networks. However, they increase the processing load at the same time. We propose a lightweight application-layer signaling protocol (lightweight-SIP) which reduces network bandwidth without sacrificing CPU performance by introducing a gateway which translates SIP into the proposed protocol. The gateway works as a cache for static and lengthy header fields of SIP messages. We expect the proposed protocol to be used by low-spec devices such as sensor nodes, less-expensive surveillance cameras and wearable computers so that it could reduce the energy consumption and lengthening the battery life or loosen requirements for the hardware specs.

Comparison of Data-Searching Algorithms for a Real-Time Information-Delivery System

The number of content-generation devices is expected to increase explosively in the near future thanks to evolution in the field of input/output devices and Consumer Generated Media (CGM) tools. Users will simultaneously wear communicating sensor devices wherever they are, whenever they need them,and whatever they are doing. Under such circumstances, various contents will be generated,updated by the devices and moved much more frequently than they are now. We propose an architecture for a real-time information-delivery system that enables users to quickly discover the freshest, most accurate content. We compared three types of well-known data searching algorithms, i.e., in DNS-like static-tree method, Web crawler method,and Chord method, which can be used in servers in existing systems to retrieve the metadata on the content.We first developed a simulator and evaluated the algorithms to assess the methods to find which generation, update, and movement of content occurred more frequently. We discovered that the Web crawler method and Chord method both offered roughly the same correct answer rate. However, the number of messages increased dramatically with the Web crawler method when the content-update interval shortened.The average search time also increased with the Chord method as the number of user nodes increased.

Peer-to-Peer SIP Features to Eliminate a SIP Sign-Up Process

We propose two features for peer-to-peer SIP in order to eliminate a sign-up process so that users can use the SIP user agent software right after installation. One is a locally generated SIP-URI which eliminates the sign-up process. Another is a feature to exchange contact addresses. It helps users to create new entries in the local address book without typing SIP-URIs. We implemented these features on SIP-Communicator with a peer-to-peer client protocol to work with a peer-to-peer SIP overlay network.