Kiyohiko Okayama

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Multihomed network is one of the most efficient configuration to improve response time of network services. However, it is hard to introduce or manage because the existing configuration methods have several problems in that they require much technical skill, involve administrative over-burden for the administrator aiid so on. In this paper, we propose a(More)
Wide spread of spam mails is one of the most serious problems on e-mail environment. Particularly, spam mails with a spoofed sender address should not be left alone, since they make the mail server corresponding to the spoofed address be overloaded with massive error mails generated by the spam mails, and since they waste a lot of network and computer(More)
NAT (Network Address Translation) is widely used as a technique that shares a single IP address in several PCs, and is widely used for alleviating the IPv4 address exhaustion and as a security solution. However, when a backbone network has access control function for PCs based on their IP addresses, it can not identify the PCs behind a NAT router since(More)
NAT (Network Address Translation) is well-known as one of the short-term solutions of IPv4 address exhaustion. NAT is a technique that shares a single IP address in several PCs, and is widely used for alleviating the IPv4 address exhaustion and as a security solution. However, when a backbone network has access control function for PCs based on their IP(More)
Wavelength Division Multiplexing (WDM) technology provides a wideband communication networks by realizing multiple communication channels with different wavelengths on a single optical fiber. In this technology, each node (wavelength router) has a finite number of transmitters/receivers dealing with different wavelengths, where each wavelength is(More)
The attempts of malicious access and attacks from the Internet to the internal computers of organizations never stop today and corresponding countermeasure for each technique is required. Most organizations introduce some firewall facilities as one of the solutions to protect their internal computers as well networks from those attacks. However, in most(More)
In recent years, with proliferation of smart phones and tablet PCs, speedup of wireless LAN communication is required for dealing with increase of traffic in wireless networks. However, transmission speed through a wireless network often slows down in comparison with that through a wired network since packets of wireless networks frequently drop due to the(More)
Recently, the Internet is widely used as a social basis and is not only providing many kinds of services but also offering these at high speed with high reliability. As one method for such a demand, multihoming technique, by which the inside network is connected with two or more ISPs (Internet Service Providers) and can use them properly according to(More)