Why does ADSL connect to the Internet at the same time?

ADSL can answer the call at the same time, but why is a disconnection caused by a call?
A: ADSL uses the frequency division multiplexing technology to separate voice and data. voice and data run on different channels, so you can receive calls while surfing the Internet, however, currently, ADSL can only be connected over a straight line phone, rather than over other telephone lines. When installing the ADSL Modem, you need to use a telephone line divider, which has three interfaces: one interface can connect to the phone box on the wall, and the other interface is used to connect to the ADSL Modem, another interface is used to connect to a telephone. when accessing the internet, only the phone number connected to the divider will not affect the line. If you use another phone number to answer the call, it will cause a disconnection. If you think it is inconvenient to use the phone, you can purchase a mother phone and connect the mother computer to the divider. In this way, you can add a child machine that can be used.