| 摘要 |
PROBLEM TO BE SOLVED: To prevent an ISDN communication charge and an Internet connection charge from being imposed on a called party telephone set. SOLUTION: A caller side ISDN terminal adaptor (hereinafter called TA) 2 discriminates whether or not an Internet call is available when a caller telephone set 1 designates a telephone number of a called telephone set 6, a predetermined number, an encrypted Internet connection membership identification number and a password are set to a setup sub address and the TA 2 transmits the set to a called party ISDN TA 5 when discriminating that the Internet call is available. When receiving a predetermined number, the called party ISDN TA 5 rings a bell of the called telephone set 6. When the telephone set 6 is hooked off, the called party ISDN TA 5 is connected to a called party access point 9 by using the Internet connection membership identification number and the password, the called party IP address acquired by the called party access point 9 is set to the setup sub address to inform the caller side ISDN TA 2 about it.
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