Mika Ishizuka

Performance study of node placement in sensor networks

The expectations for sensor networks are growing. One of the most important issues in sensor networks is to evaluate the fault tolerance and built technology to improve it, because sensor nodes are prone to fail and have limited power capacity. So far, research on the fault tolerance has focused on battery exhaustion. Since placement affects whether there are nodes that can sense and routes to the base station, placement of sensor nodes is also important. However, there has been little research on the placement of sensor nodes and all of it is based on deterministic placement, which is not realistic when many sensor nodes are placed in a large area. In such a situation, stochastic placement is needed. Therefore, this paper evaluates the tolerance against both random failure and battery exhaustion from the viewpoint of stochastic node placement.

Characteristics of ABR explicit rate control algorithms in WAN environment

This paper investigates the characteristics of ABR explicit rate control algorithms in the WAN environment. We also propose two new control algorithms based only on traffic measurement. An ABR service is expected to make it possible to utilize bandwidth effectively by closed-loop congestion control, and several control algorithms have been proposed. However, for WAN environment, a long propagation control delay will affect the effectiveness of control algorithms. Additionally, if a network supports large numbers of connections, some of the algorithms may not work well. Thus, we first categorize the aim and mechanism of control algorithms, including our proposed algorithms. Then, we evaluate their characteristics by simulation in WAN environment from the viewpoint of throughput, robustness, quickness, stability, and fairness. Using this analysis, we discuss their effectiveness in WAN environment.

Dynamics of TCP flow control over high-speed ATM networks

TCP performance over high-speed ATM networks is evaluated. In TCP over UBR (unspecified bit rate), packet losses caused by congestion deteriorates throughput and fairness. Even if early packet discard (EPD) is added, fairness still remains as a problem as long as cell loss occurs. TCP over ABR(ER) (available bit rate-explicit rate) can provide high performance by suppressing cell loss, as long as ABR rate control does not interact with TCP flow control. Coarse timer granularity and large window size can avoid the interaction. When end-to end ABR is not available, further enhancement of TCP control using implicit or explicit congestion notification is needed for performance improvement.

Capacity dimensioning of VPN access links for elastic traffic

In this paper, we are studying the capacity dimensioning of virtual private networks (VPN) access-links for elastic traffic, such as the Web or ftp. Under the assumption that the core-VPN network is provisioned with sufficient large capacity, the capacity management of the VPN access link is a matter of bandwidth-sharing for elastic traffic of the two bottleneck links, the ingress and egress access links, the processor -sharing model gives a simple formulae of mean transfer time, but in our case, the value may be less than the actual transfer time. In contrast, max-min fair sharing provides an accurate sharing model which is similar to the TCP, but it is difficult to obtain a closed form of performance statistics. We propose a closed form approximation for a max-min fair sharing model, in a specific but realistic topology, by investigating the difference between the max-min and the processor sharing model. Using the approximation, we are performing the capacity dimensioning of VPN access links.

Simulated performance of TCP over UBR and ABR networks

The performance of the Transmission Control Protocol (TCP) over the Unspecified Bit Rate (UBR) and the Available Bit Rate (ABR) ATM service classes was investigated by simulation. These service classes are both for data communication but have different characteristics. It is therefore important to reveal the performance of TCP over UBR and ABR.

Leveraging real-world data while protecting privacy Framework using personal agent system for distributed data

We propose a real-world data exchange framework based on the concept of data ownership. The most important issues with these data are the protection of user privacy and preserve the value of the information derived from the data to consumers. This framework enables the protection of privacy and enables maximum leverage of real-world data belonging to each person at the same time. In our framework, real-world data and its information value are managed and protected by the personal agent system that works on each persons authority. On that basis, the information value can be exchanged and leveraged using a market mechanism that distributes transactions of queries and answers concerning the data. We also present the basic design of the framework and its personal agent system that works on multiple user devices.