Communication apparatus

A communication apparatus configured to communicate with a first communication apparatus different from the communication apparatus via both of a public switched telephone network (PSTN) and an internet, the communication apparatus comprising:

• a requiring section configured to transmit, from the communication apparatus to the first communication apparatus, a requirement for establishing a state in which the first communication apparatus is allowed to communicate with the communication apparatus via the internet, the requirement being transmitted from the communication apparatus to the first communication apparatus via the internet by using an IP address of the first communication apparatus;
• a first communication establishing section configured to establish a state in which the communication apparatus is allowed to communicate via the internet with the first communication apparatus that has accepted the requirement transmitted by the requiring section;
• a calling section configured to transmit a dial signal of a first identification number to a switch via the PSTN to call a first-identification-number assigned apparatus when the first communication establishing section has established the state in which the communication apparatus is allowed to communicate with the first communication apparatus, wherein the first identification number is an identification number of the a first-identification-number assigned apparatus used on the PSTN and the first identification number is associated with the IP address of the first communication apparatus and the switch is placed on the PSTN;
• a notifying section configured to transmit a notification about calling of the communication apparatus, from the communication apparatus to the first communication apparatus via the internet after the calling section has called;
• a first receiving section configured to receive a called-acknowledgement-signal from the first communication apparatus, wherein the called-acknowledgement-signal is transmitted from the first communication apparatus to the communication apparatus via the internet when the first communication apparatus has received the notification and the first communication apparatus has been called via the PSTN;
• and
• a communication controlling section configured to control communication of the communication apparatus with the first communication apparatus via the PSTN when the first receiving section has received the called-acknowledgement-signal transmitted from the first communication apparatus.