Recently, use of an access network, which is a large-capacity communication broadband such as Asymmetric Digital Subscriber Line (ADSL) and optical fiber, and is always connectable, has rapidly spread among home users. In the conventional method of the Peer-to-Peer communication, the communication terminals are connected via a network to perform direct communication. One of the examples is that, in order to resolve an address of the terminal apparatus on the other end of the communication, a server is utilized or another communication terminal is inquired of the address through relaying (e.g., Japanese Laid-Open Publication No. 2003-158553).
FIG. 17 shows a communication system using the conventional IP telephone apparatuses described in the above-mentioned reference. For example, in the case when an IP telephone apparatus 10A calls an IP telephone apparatus 10C, the IP telephone apparatus 10A obtains an address of the IP telephone apparatus 10C by inquiring IP telephone apparatuses 10B, 10C and 10D based on the phone numbers. Each of the IP telephone apparatuses is equipped with a Peer-to-Peer communication apparatus for sending and receiving information based on the Peer-to-Peer method via an IP network, a phone number search apparatus for verifying the correspondence between the phone number received by the Peer-to-Peer communication apparatus and the phone number of the IP telephone apparatus. The Peer-to-Peer communication apparatus sends back the IP address of the IP telephone apparatus only in the case when the phone numbers match as a result of verification.
The structure of the IP telephone apparatus shown in the patent literature mentioned above, however, faces a problem that the IP phone 10A can obtain the address of the IP telephone apparatus 10C without a permission of the IP telephone apparatus 10C. Such problem is notable especially in the case when the user of the IP telephone apparatus 10A is an ill-intentioned person. In this case, information related to an attack such as Denial of Service attack (DoS attack) is given to the IP telephone apparatus 10C.
Another problem is that a manager such as an agent who manages the Peer-to-Peer communication cannot know how long the IP telephone apparatus 10A communicates with the IP telephone apparatus 10C, and thus cannot manage the communication.
It is yet another problem caused in using the conventional IP telephone apparatuses that, in some cases, it is impossible to achieve real-time connection since it requires time for the conventional IP telephone apparatus to obtain information such as an IP address of a connected communication terminal when the connecting communication terminal communicates with the connected communication terminal using phone numbers.