1. Technical Field
The present invention relates to an IP telephone apparatus using VoIP, and particularly to its reception functions.
2. Background Art
Continuous Internet connection services utilizing broadband technologies such as ADSL (Asymmetric Digital Subscriber Line) are now widespread. Progress has also been made in the VoIP (Voice over Internet Protocol) technology, in which voice is transmitted in accordance with IP (Internet Protocol). As a result, IP telephone based on the Internet is now commonly utilized. IP telephone provides for three modes of communication, namely communications between personal computers, communications between a personal computer and an ordinary telephone machine, and communications between ordinary telephone machines.
Now referring to FIG. 8, an IP telephone system will be described in connection with the case that a phone call is made from an analog telephone 83 on the call originating side to another analog telephone 89 on the call destination side. Analog telephone 83 on the call originating side converts voice into an analog signal and transmits it to a VoIP gateway 84. VoIP gateway 84 converts the analog signal into a digital signal in order to generate an IP packet signal. The IP packet signal is sent out via a router 85 to the IP network, where the IP packet signal is transferred successively while its destination IP address is referred to in the same manner as in the case of a conventional IP packet. The IP packet eventually arrives at a router 87 on the call destination side.
Router 87 on the call destination side transmits the IP packet signal to a VoIP gateway 88 on the call destination side. VoIP gateway 88 converts the digital signal into an analog signal, which is opposite to the operation of VoIP gateway 84 on the call originating side. The analog signal is then transmitted to analog telephone 89 on the call destination side, which converts the analog signal into a voice signal.
Analog telephone 83 and VoIP gateway 84 may be substituted by a personal computer or a mobile communications terminal equipped with IP telephone software, or an IP telephone machine.
In the IP telephone system, there is provided a call control server 81 for performing a “call control,” as shown. Call control server 81 includes a database 82 that provides a correspondence table between telephone numbers and IP addresses. Call control server 81 has the functions of verifying VoIP gateways 84 and 88 as well as the user, managing telephone numbers and IP addresses, and managing accounting information, for example. VoIP gateways 84 and 88 perform the “call control,” such as calling the other party and managing communications. The “call control” employs a “call control protocol.” Various kinds of call control protocols are known, such as H.323, SIP, and MEGACO.
A call control sequence will be briefly described. Upon reception of a call originating from analog telephone 83 on the call originating side, VoIP gateway 84 on the call originating side communicates with call control server 81 to make sure that it is possible to communicate with the call destination side and then exchanges information regarding the conversion of a telephone number and an IP address, for example. Then, call control server 81 communicates with VoIP gateway 88 on the call destination side to see if it is possible to communicate with the call destination side, for example. If it is confirmed that the call destination side can receive the call, the call from the call originating side to the call destination side is made, followed by an actual conversation and an exchange of control information such as call session management information.
Currently available telephone machines, such as mobile phones or fixed phones, are provided with a variety of functions, in addition to the voice call function. For example, some phones are capable of changing the ringtone depending on the originating caller by utilizing their own telephone directory. In case that the destination caller cannot receive the call, a response may be made by an answerphone function provided in the telephone. Instead of the answerphone function provided in the telephone, an answerphone service provided by a telephone service provider may be utilized. Some telephone service providers offer a service of transferring a call to a pre-designated telephone number (of a cellular phone, fixed phone, or PHS, for example).
(Patent Document 1)
JP Patent Publication (Kokai) No. 9-321914 A (1997)
(Patent Document 2)
JP Patent Publication (Kokai) No. 11-103348 A (1999)