Kiyohiko Okayama

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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)
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)
With the explosive widespread of the Internet, many fundamental and popular Internet services such as WWW and e-mail are becoming more and more important and are indispensable for the human's social activities. As one technique to operate the systems reliably and efficiently, the way of introducing multihomed networks attracts much attention. However,(More)
In recent years, spam mails intending for ``One-click fraud" or ``Phishing" have become increasing. As one anti-spam technology, DNSBL based on the URLs or their corresponding IP addresses in the messages is well used. However, some spam mails that cannot be filtered by conventional DNSBLs get appearing since the spammers create websites using various(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)
In recent years, many spam mails intending for ``One-click fraud" or ``Phishing" have been sent to many unspecified e-mail users. As one anti-spam technology, URL Blacklist based on the URLs in the spam mails is well used. However, spammers have been avoiding this technique by getting many new domains, using them only in a few spam mails, and throwing them(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)
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 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)