Tsunehiko Chiba

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Mobile users require secure and seamless mobility access as they move across heterogeneous access networks such as IEEE 802.11, code division multiple access (CDMA2000), worldwide interoperability for microwave access (WiMAX), and general packet radio service (GPRS). However, additional complexity of the underlying networks and the variety of security and(More)
Real-time services such as VoIP and multimedia streaming are affected during a mobile's rapid handoff due to the associated delay resulting from associated handoff operations of discovery, detection, configuration, registration, media redirection, and processing at different network nodes. Redundant communication path of any signaling and media adds to the(More)
While there have been tremendous efforts to develop the architecture and protocols to support advanced Internet-based services over 3G and 4G networks, IMS is far from being deployed in a wide scale manner. Effort to create an operator controlled signaling infrastructure using IP-based protocols has resulted in a large number of functional components and(More)
Recently, femtocells, which cover a cell area of several tens of meters, have been attracting considerable attention in mobile communications. When a femtocell is connected through a public network, such as a broadband access network or the Internet, a secure tunnel is established between the femtocell and the security gateway located in the mobile core(More)
The User-Generated Contents (UGC) and User-Generated Services (UGS) concepts allow end-users to create their own contents and services as well as to share and to manage the lifecycle of these services. Web Services paradigm has been widely used for services composition in Internet to create Web applications that are flexible and rapidly deployable. In(More)
The Web Services composition paradigm has been widely used in Information Technology (IT) and Internet environments to create Web applications that both flexible and rapidly deployable. Web Services are a key way to realize Service-Oriented Architectures (SOA). In Telecom, on the other hand, the IMS (IP Multimedia Subsystem) architecture enables(More)
Recently, small base stations such as femtocell and picocell are drawing attention as new components of wireless access networks. These small base stations are used not only to expand the wireless area within a large building, but also to increase bandwidth capacity and reduce the load on the core network. If multiple femtocells are deployed in an office(More)