Why is there such a big difference between telephone dialing and ADSL (both telephone lines)?

Dial-up Internet access with a 56kbps modem is narrowband, because the theoretical channel bandwidth of the 56kbps modem is only 56kbps, and the theoretical transmission capacity is 56k/8=7k/ s when converted into byte traffic. This speed can only meet the transmission of a small amount of text information, and cannot carry a large amount of data such as video, audio and image information.

In order to solve the problem of network transmission with a large amount of information, network operators have developed ADSL data communication services and other high-bandwidth data transmission services to meet people's demand for audio, video and image information transmission. Generally, the bandwidth above 1 Mbps (baud rate 1024 m) is called broadband.

ADSL is a kind of broadband, but its performance is only the middle level of broadband products at present. The top layer is local area network and wireless local area network (including optical fiber), the next layer is CM (wired broadband), the next layer is VDSL (including ADSL), the next layer is mobile network (but it will be faster than VDSL after 3G), the next layer is ISDN, and finally dial-up Internet access.