FPN (Flexible Private Network) is our coinage to indicate a system which can realize flexible and secure communication groups. There is a similar terminology called "VPN" (Virtual Private Network), which is used as a technology to ensure safe communication routes between location-fixed sub-networks or between a fixed server and remote users (see Fig.1). However, in the ubiquitous society in future, establishment of a more flexible system rather than a fixed system like VPN will be required. For instance, there are cases where both of the communicating persons move around. Other cases are that some users in a specific sub-network communication group belong to another personal communication group individually. Although communication groups can be defined in advance, it is desired that management load does not occur, even if some changes in system structure or users' movement take place, as long as such definitions of communication groups remain the same (Fig.2). We named this kind of system concept as FPN.
It is difficult to realize the FPN concept with the existing technologies alone. For example, IPsec, which is the main technology for VPN, is not suitable for such a case as management load is large when system structure changes frequently, although its security level is strictly high. In case of mobile IP which enables mobile communication, it needs special address controlling equipment called HA (Home Agent). Another problem for mobile IP is that communication packets must go through redundant routes. Therefore its introduction is in fact not very easy. As a result, realization of FPN, which is easy to introduce and requires only a small amount of management load while maintaining a moderate level of security, is desired. Although there are many ways to realize FPN, our Laboratory proposes a secure communication architecture of our own designing named "GSCIP" (Grouping for Secure Communication for Internet Protocol; We pronounce this like "G-skip".).