Session Initiation Protocol (SIP), a protocol used in VoIP (Voice over IP) communications, enables a caller to send a SIP message to a callee with his/her UserID concealed from the callee, which in turn, prevents A SIP server from making an attempt to manage the caller. If the same IP Telephone address is used whenever the IP call is made, a third party may guess the IP address easily during conversation. The SIP message sent by the caller is converted and conversion tables are managed by the SIP server. The IP Telephone modifies its IP address for each IP call. Thus, the caller can make a call to the callee with his/her UserID concealed from the callee using the SIP server with a message conversion function and communications carriers having SIP servers installed to manage the callers using their conversion tables. It is difficult to any malicious third party to guess the IP Telephone address, because the IP Telephone address is modified for each call.

A terminal acquires a network prefix of a network connected thereto, and determines whether that network prefix is identical to an initial network prefix. When the terminal determines that the two prefixes are different, the terminal reads the network prefix of each of a destination address and a source address in a received packet. When the read network prefix is different from the initial network prefix, the terminal substitutes the initial network prefix for the read network prefix, thereby generating a pseudo header. The terminal authenticates the received packet using the generated pseudo header.

A system and method for fast GPRS for IPv6 may improve data transfer efficiency in mobile networks, for example, in networks that relay on the GPRS infrastructure as defined and standardized in the European Telecommunications Standards Institute (ETSI), and on mobile IPv6 as standardized in the IETF. Mobile IPv6 techniques may be applied in the context of GPRS to transform mobility management into a routing problem, for example, by translating the routing area identifier into a part of the routing prefix in IPv6. Similar mobile IPv6 techniques also may provide an evolution path toward internetworking using native mobile IPv6.

There are provided an apparatus and method for automatically configuring virtual addresses for a duplicate address when the duplicate address is detected in a single subnet. The apparatus in a non-configured node includes a duplicate address search message transmitter, a duplicate address response message receiver, a virtual address allocation message transmitter, and a virtual address response message receiver. The apparatus in a configured node includes a duplicate address search message receiver, a duplicate address response message transmitter, and a virtual address response message receiver. The apparatus in a router includes a virtual address allocation message receiver, a virtual address allocator, and a virtual address response message transmitter.

A wireless communication system includes a plurality of base stations, a mobile wireless communication device which makes wireless communication with the base stations, a terminal device, and a router through which the base stations make communication with an IP network. The terminal device transmits an address thereof to the mobile wireless communication device, before the mobile wireless communication device makes link with one of the base stations. The terminal device fabricates a frame addressed to an address of the router, and transmits the frame to the router, after the mobile wireless communication device has made link with one of the base stations. The router transmits an address thereof to the base stations, before the mobile wireless communication device makes link with one of the base stations. The router fabricates a frame addressed to an address of the terminal device, and transmits the frame to the terminal device, after the mobile wireless communication device has made link with one of the base stations.