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The communications environment is currently well organized. Still, it is not easy to handle requirements for urgent communications in a disaster. In a large-scale disaster, it is highly probable that communications functions will be hampered, making access to communication links itself difficult. There is a need for studies directed at assuring robustness and reliability in the emergency communications system. This paper proposes an access protocol for wireless networks in which the centralized control hierarchical network and the horizontal connection ad hoc network are combined. The routing method in which a terminal that cannot directly communicate with the base station (BS) sends urgent data to the BS through neighboring terminals, and an access control protocol for multihopping, are described. In the proposed scheme, the terminal monitors communications in neighboring nodes and dynamically generates a route based on the number of hops to the BS. Evaluations show that the percentage of terminals that can reach the BS by multihopping involving a few hops is significantly improved. It is also shown that the terminal knows the number of hops to the BS in the proposed method, which makes it possible to predict the throughput and the delay time, which is a property suited to urgent communications. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(7): 52–64, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20141 [ABSTRACT FROM AUTHOR]

IP traceback is a technique to combat distributed denial of service attacks. This technique can specify the routers in the path of the attack flow with forged source addresses. Although several techniques have been proposed to solve this problem, a variety of problems arise when operating on the actual Internet. We proposed a hierarchical architecture for IP traceback as a solution to these problems. In this paper, we define each type of protocol, design architecture for a prototype implementation, and verify its operation. Based on the results, we found that a large-scale simulation was needed. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(11): 49–56, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10202 [ABSTRACT FROM AUTHOR]

In order to realize high-speed Internet access on PTMP access networks such as bidirectional CATV, the Synchronous CSMA/CD method has been developed. The main points are that, when multiple packets collide, the collision state always starts from the head of the colliding packets by synchronizing the arrival of the packets at the hub device with the predetermined timing, and that the hub device always monitors the access status of the uplink and broadcasts the status through the downlink. As a result, the CSMA/CD method can be applied to PTMP networks, and the maximum network length can be arbitrarily set without dependence on the minimum packet length. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(6): 43–51, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10074 [ABSTRACT FROM AUTHOR]