Hitomi Tamura

Performance Evaluation of Power Saving Scheme with Dynamic Transmission Capacity Control

Our major purpose in this study is to develop a method for achieving power conservation with a network itself. The proposed power saving approach takes traffic characteristics of network into consideration. If network switch can adapt its processing speed to arrival traffic rate, power saving can be expected depending on the network utilization. The same idea is already materialized just as Intel’s Speedstep technology [5]. We first confirm this consideration by measuring the power consumption of some switches and show that a Giga bit Ethernet port consumes 2 or 3 W with an addition of a link. Based on this experiment, we propose a scheme to achieve the dynamic control of the transmission capacity between switches in order to reduce the power consumption based upon the change in traffic volume. To control the transmission speed dynamically and gradually, Link Aggregation is used in our scheme. From simulation studies, we show that the proposed architecture can achieve both high power saving capability and sufficient feasibility.

Virtual segment: Store–carry–forward relay-based support for wide-area non-real-time data exchange

Abstract We have proposed the concept of the virtual segment (VS), in which a global communication service is provided by combining a store–carry–forward scheme using vehicles with broadband wireless/wired network infrastructures along roads connected to the Internet. The VS can be a practical framework for non-real-time, asynchronous message transfer (especially for large messages) in a cost-effective manner. In this study, a critical implementation design issue, the message forward scheduling, in the VS approach is discussed and investigated through computer simulation by our developed VS simulator that has reflected the results of the field experiment for realistic performance evaluation.

Deployment Design of Wireless Sensor Network for Simple Multi-Point Surveillance of a Moving Target

In this paper, we focus on the problem of tracking a moving target in a wireless sensor network (WSN), in which the capability of each sensor is relatively limited, to construct large-scale WSNs at a reasonable cost. We first propose two simple multi-point surveillance schemes for a moving target in a WSN and demonstrate that one of the schemes can achieve high tracking probability with low power consumption. In addition, we examine the relationship between tracking probability and sensor density through simulations, and then derive an approximate expression representing the relationship. As the results, we present guidelines for sensor density, tracking probability, and the number of monitoring sensors that satisfy a variety of application demands.

Virtual Segment: Store-Carry-Forward Relay-Based Support for Wide-Area Non-Real-time Data Exchange

In the Internet of the future, a flexible, dynamic combination of wireless and wired access networks is expected to be a key driver for enlarging the broadband communication service area. However, in general, the number of broadband wireless access points is limited due to their cost, and hence, they cannot cover the whole network. On the other hand, various message delivery schemes based on store-carry-forward routing with some extensions have been studied to support nonreal- time communication in sparse or intermittent networks. However, communication services based solely on the storecarry- forward schemes covering a large area are inefficient because the delay time for message delivery increases in proportion to the size of the service area. Therefore, to extend the communication service area with controllable performance in a cost-effective manner, the authors have proposed a concept of Virtual Segment (VS) in which global communication service is provided by combining a store-carry-forward scheme with broadband wireless/wired network infrastructures connected to the Internet to deploy the supplementary infrastructure. Along this line, in the present paper, the issues on the addressing and the message transfer methods in VS approach are considered which are essential for designing a practical framework for non-real-time, asynchronous data communication, especially for large-sized message transfer. A logical architecture for implementation is also presented. Finally, the message transmission methods are examined using computer simulation.

Design of Wireless Sensor Network for Multi-Point Surveillance of a Moving Target Based on the Relationship Between Tracking Probability and Sensor Density

In this paper, we focus on the problem of tracking a moving target in a wireless sensor network (WSN) in which the capability of each sensor is relatively limited in order to construct large-scale WSNs at a reasonable price. In our prior study, we proposed a simple multi-point surveillance scheme for a moving target in a WSN and demonstrated that the scheme achieved high tracking probability with low power consumption. However, we have not suggested guidelines for designing the WSN to completely satisfy the wide range of user requirements. Therefore, in this study, we examine the relationship between tracking probability and sensor density through simulations, and then derive an approximate expression representing the relationship. As a result, we show guidelines for sensor density, tracking probability, and the number of monitoring sensors that satisfy a variety of application demands.

Path selection scheme for traffic load distribution considering the characteristics of network topology

Congestion inherently occurs on the network that are shared among several autonomous users due to traffic concentration on certain links. Such an imbalanced traffic load can be caused by network topological features or frequently and independently changing traffic loads. In terms of the topology, it has recently been demonstrated that the Internet has the scale-free property in its topology, which is defined by a power-law distribution in the number of links per node. In the present paper, we focus on the effect of the scale-free property on the traffic load concentration, and study Traffic Engineering (TE) scheme to address such issue. We propose a path selection scheme for traffic load distribution, which is a sort of TE scheme, considering the scale-free property of the network topology. The simulation results show that the proposed scheme is very effective in distributing the traffic load over scale-free networks.

A Simple Multi-point Surveillance Scheme of a Moving Target for Wireless Sensor Networks

We consider the problem of moving target tracking in a wireless sensor network (WSN) in which the capability of each sensor has relatively limited performance enabling us to construct large-scale systems/networks at reduced cost. In order to achieve moving target tracking with high resolution, the following two requirements must be satisfied: (I) Multipoint surveillance with the appropriate number of sensors, which depends on the characteristics of the applications and user requirements, and (II) Dynamic switching and quick decision-making of monitoring sensors in response to the movement of the target. In the present paper, we propose a simple and robust multi-point surveillance scheme for moving targets in WSNs. Through simulation experiments, we demonstrate that the proposed scheme can quickly and precisely assign monitoring sensors on a WSN of any density with low power consumption in response to the movement of the target, thereby maintaining high tracking probability even for high-speed targets.

Analysis of two-phase path management scheme for MPLS traffic engineering

Multi-Protocol Label Switching (MPLS) is suitable for implementing Traffic Engineering (TE) to achieve two goals: Quality of Service (QoS) provisioning and the efficient use of network resources. In fact, MPLS allows several detour paths to be (pre-)established for some source-destination pair as well as its primary path of minimum hops. Thus, we focus on a two-phase path management scheme using these two kinds of paths. In the first phase, each primary path is allocated to a flow on a specific source-destination pair if the path is not congested, i.e., if its utilization is less than some predetermined threshold; otherwise, as the second phase, one of the detour paths is allocated randomly if it is available. Therefore, in this paper, we analytically evaluate this path management scheme by extending the M/M/c/c queueing system and we investigate the impact of a threshold on the flow-blocking probability. Through some numerical results, we discuss the adequacy of the path management scheme for MPLS-TE.

Performance analysis of IP datagram transmission delay in MPLS: impact of both the number and the bandwidth of LSPs of layer 2

LSR (label switching router)s in MPLS (multiprotocol label switching) networks map arriving IP flows into some labels on the layer 2 switching fabric and establish LSP (label switching path)s. By using LSPs, LSRs not only transmit IP datagrams fast with a cut-through mechanism, but also solve the traffic engineering issue to optimize the delay of some IP datagram flows. So far, we have analyzed the performance of LSR focusing only on the maximum number of LSPs which can be set on layer 2. We also consider the bandwidth allocated to each LSP and analyze the IP datagram transmission delay and the cut-through rate of LSR. We suppose the label mapping method as the data-driven scheme in the analytical model, so that the physical bandwidth of LSR is shared by both the default LSP for hop-by-hop transmission and the cut-through LSPs. Thus, we investigate the impact of the bandwidth allocation among these LSPs on the performance.

Packet-level forward erasure correction with user fairness in lossy wireless networks

Packet-level erasure correction is considered for downstream packets each of which is delivered from a base station to an individual receiver (i.e., user) over a lossy shared wireless network where only a very limited upstream feedback is provided. Note that, while the destination of each packet is a single user, each packet can be overheard by all users in the shared network. With exploiting this overhearing property of wireless links, we focus on packet recovery by exclusive-OR (XOR) packet composition-based forward-erasure-correction (FEC). For network applications with packet-loss tolerance and delay-time limitation, our goal is to increase the effective packet received rate (the ratio of finally received/recovered packets after applying FEC) of each user with fairness in a low-cost manner. We propose a simple XOR packet composition scheme that can approximately maximize the minimum effective packet received rate among users, based on an experimentally suggested linear relation between the packet loss rates and the optimal packet composition ratios among users. Simulation results clearly indicate the potential effectiveness of the proposal.