The wireless LAN (WLAN) system based on IEEE802.11 uses multiple transmission rates to obtain improved communication quality according to the communication environment. Furthermore, the range of use of wireless LAN is rapidly expanding in daily life, and it has become an important infrastructure for safe and secure life. However, because the dynamic change in transmission rate depends on variation in the communication environment, it is difficult to implement this transmission rate model in typical simulators, making it impossible to sufficiently simulate the real environment using the existing transmission rate model. To address this issue, this study first evaluates the characteristics of transmission rate over the multi-rate environment using real machines. We then propose a transmission rate model for the multi-rate environment based on the experimental results. In this study, we show a transmission rate model using an advection-diffusion equation. Note that there is an effort to use Wi-Fi systems at the time of disaster. Our proposed model is useful for the design and the operation of such Wi-Fi systems. Next, our simulation results confirm that the proposed transmission rate model can replicate the performance achieved in the actual environment.

This paper reports spoofing attacks that exploit a vulnerability of the controller area network (CAN) protocol, which is often used in in-vehicle networks. However, authorized electronic control units (ECU) should be able to detect anomalous CAN message traffic. We focused on ECU states used for error handing. Bus-off attacks against the ECU have been proposed to induce transmission errors, and then transit the state of the target ECU to the bus-off state, in which the ECU cannot access the CAN bus. The attack combining the bus-off attack with the spoofing attack could not be detected by the authorized ECUs, and would consequently be a potential threat for the vehicle. In this paper, we propose a spoofing attack method that uses a bus-off attack and is not detected by the authorized ECUs. Based on the proposal, we implemented an attacker prototype using a field-programmable gate array. In a laboratory setting, we verified the attack in a simulated environment consisting of the attack hardware and ECU, and evaluated the effect of spoofing and the behavior of an actual car. The results showed that the transmission of regular messages was completely prevented, and the percentage of spoofing messages could be made 100%; that is, no error was detected in the ECUs of the car. We have verified the feasibility of the proposed method and the potential threat for actual cars. In the future, we will conduct studies to prevent vehicles from such attacks.

Wireless local area networks (WLAN) based on IEEE 802.11 usually employ carrier sense multiple access with collision avoidance (CSMA/CA) for media access control. In the CSMA/CA mechanism, data frame collisions often occur if the number of wireless terminals increases. This problem decreases the total throughput of terminals connected to the same access point. To address this problem, a media access control method based on the synchronization phenomena of coupled oscillators (SP-MAC) has been proposed. Previous studies have confirmed that SP-MAC can significantly decrease the number of data frame collisions and improve total throughput compared to CSMA/CA. However, the previous studies did not consider a QoS control based on SP-MAC. This study focuses on throughput as a QoS metric. This study proposes a control method to guarantee throughput based on SP-MAC. Furthermore, this study evaluates the effectiveness of the proposed method through simulation experiments. The simulation results demonstrate that the proposed method can control the throughput of each terminal without decreasing total throughput. Furthermore, this study shows that the proposed method can guarantee throughput for a specified terminal.

Public areas, such as train stations and airports, providing wireless Local Area Network (WLAN) services are increasing and expanding because of the rapid development of WLANs based on IEEE 802.11 standard. Moreover, because of the advances in smartphone tethering technology, portable access points (APs) such as mobile Wi-Fi routers are being utilized more frequently. Consequently, there are increasing circumstances where a user needs to select and connect to one of the many APs. AP selection significantly determines the quality of service of the subsequent communication session. Existing AP selection algorithms consider user movement but not AP movement. We propose an AP selection method that handles both types of movement effectively. Moreover, we show that the proposed method improves the throughput significantly compared to the existing method.

The technology of flow-based QoS control on wireless LANs is receiving a lot of attention. There are several QoS technologies that can provide bandwidth guarantees by using TCP congestion control (QoS-TCP) and MAC control (QoS-MAC). Unfortunately, since QoS-TCP runs on the end terminal, it is possible that QoS-TCP will attempt to guarantee bandwidth without the permission of the network administrator (e.g. a hotspot service provider). In such a case, it is possible that these flows compress the throughout of coexisting flows unfairly. That is, it is possible for a non-priority flow to claim to be a priority flow by using QoS-TCP without the permission of the network administrator. We call such flows greedy flows. The purpose of this study is restraining such greedy TCP flows by using QoS-MAC over the wireless LAN network. This study evaluates the performance of our proposal by using ns-2. Simulations show that the proposal can control the greedy flows by using a QoS-MAC.

Walking is a fundamental human ability necessary for everyday life. We have developed an omnidirectional walker (ODW) for walking support to those who have walking disabilities. It is necessary for the ODW to know which direction the user is intending to go during walking support. A novel interface is proposed for the ODW to recognize directional intention according to the user's forearm pressures which are measured by force sensors embedded in the armrest. The relationship between forearm pressures and directional intention was extracted as fuzzy rules and an algorithm is proposed for directional intention identification based on distance type fuzzy reasoning method. In this paper, we conduct walking support experiments with the proposed method. The results show that the algorithm is applicable to directional control in walking support.

Satellite link speeds are now increasing in unison with those of terrestrial links. For example, the maximum link speed of WINDS (Wideband Internetworking engineering test and Demonstration Satellite) which was launched on 2008 is 1.2 Gbit/s. WINDS is expected to support applications in education, medicine including telemedicine, and disaster countermeasures. Therefore, such satellite communication service is one of the key technologies for network assurance. TCP-STAR was proposed to improve the throughput over satellite Internet. However, no experimental evaluation of TCP-STAR over satellite links such as WINDS has been published. Therefore, this paper evaluates the performance of TCP-STAR by comparing with TCP-New Reno and TCP-Hybla over a network consisting of WINDS, HDR-VSAT, and portable VSAT. As a result, it is found that TCP-STAR and TCP-Hybla achieve better throughput when segment losses do not occur, while TCP-STAR achieves the best throughput when segment losses occur.

We have already proposed the framework of autonomous decentralized control based on local-interaction as a novel control mechanism for communication networks. This framework is based on the relation between local interaction and the solution yielded by a partial differential equation. In this framework, the state of the complete system is controlled by appropriately designing the autonomous operation of the subsystems. That is, the local action rules (micro-level) are designed to produce an appropriate state of the whole system at the macro-level. Our previous studies proposed diffusion type flow control (DFC) as a solution for the extremely time sensitive flow control required by high-speed networks and we have evaluated the performance of DFC by simulation. In this paper, to apply DFC to real networks, we show the technique to implement the DFC functions on PCs and to investigate its performance in the presence of TCP.

"Parallel downloading" is one of the most effective technologies which speed up downloading large files on the Internet. As ubiquitous networks will be realized in the near future, downloading large files quickly is also very important on various types of networks. However, if we use the parallel downloading method on dynamic networks, such as ad hoc networks, it will not work well because of high loss rate and delay. To address this issue, we adopt UDP as a transport layer protocol instead of TCP which guarantees perfect in-order delivery unnecessary for file downloading. We have implemented a prototype of the parallel downloading method using HTTP over UDP, and it is confirmed that our method outperforms the traditional method which adopts TCP, especially when loss rate is high and delay is large. Our proposal will be effective on dynamic networks such as ad hoc networks included in the ubiquitous network environments

In mobile ad hoc networks, routing schemes using location information have been proposed. Most of these schemes assume that the source node already knows the location information of the destination node. However, since all nodes are always moving, it is difficult to apply this assumption to the real mobile ad hoc environment. In order to cope this difficulty, this paper presents a new routing scheme HRLI, a Hybrid Routing with Location Information, which using the threshold for the communication range of all nodes. And it considers the location and velocity information of the destination node and the neighboring nodes. In HRLI, when a source node creates a route to a destination node, the future location of the destination node predicted by the source node is calculated using these location and velocity information. And the source node sends data packets based on the predicted location information of destination node and neighboring nodes. This paper shows that HRLI achieves high data delivery ratio and fewer overheads for using the threshold of communication range and the predicted location through simulation experiments

As a variety of communication devices emerging, we can easily install two or more communication interfaces on a PC or a PDA and make a multi-home environment. To utilize this multi-home environment effectively, SCTP (stream control transmission protocol) has been proposed and standardized. Extending functions of the original SCTP, a strategy which can adapt SCTP to real-time communications has been proposed. However, the typical existing strategy has not enough considered the switching conditions from the viewpoint of transmission delay, so there is room to improve them. In this paper, we clarify the drawbacks of the existing strategy and their influences on the performance. Then, we propose a new strategy of path switching to reduce the delay and to increase the amount of data successfully delivered. The effect of the proposed strategy is discussed and confirmed through experimental evaluations.

As the Internet users increase, asymmetric networks which provide asymmetric bandwidth or delay for the uplink and downlink have become a great attraction. However asymmetric networks which use both terrestrial and satellite links at the same time have not been adequately investigated. Therefore, this paper proposes a new formula for TCP performance evaluation for the asymmetric networks. Using this evaluation formula, we calculate the throughput of TCP Reno over the asymmetric networks taking slow start into account. The calculation results are compared with the following: (1) the value based on an existing theoretical formula, (2) the outputs of simulation by NS (Network Simulator), and (3) the experimental results using VSAT (Very Small Aperture Terminal) satellite communication system for satellite links and the Internet for terrestrial links. As a result, it is shown that the new formula is more precise than the one already proposed.

In this paper, we present a routing protocol for finding two node-disjoint paths between each pair of nodes in a computer network. In the proposed protocol, each node in the network has the same procedure, which is driven by local information with respect to the network topology such as an adjacent node on a spanning tree in the network. Thus, the execution of the protocol can continue after changes of the network topology and load. The concept of spanning tree-based kernel construction is introduced to synchronize procedures under the distributed control of the protocol. The routing scheme based on the protocol possesses the enhanced capabilities of alternate routes and load splitting, which cope with failures and load variations in the network. Furthermore, even if topology changes occur which damage the obtained disjoint paths, the paths themselves can be updated efficiently.