The common specifications of telephone lines are two-core and four-core, with diameters of 0.4 and 0.5 respectively, and 0.8 and 1.0 in some areas. In addition to two and four cores, there are four, six, eight and ten cores. In general, if the household is in the local mode, 2 cores are enough. If it is used by the company or some group phones, considering the need for broadband use, it is recommended to use 4-core telephone lines. If it is used by digital phones, it is recommended to use 6-core telephone lines.

The telephone line passes through ADSL, converts the information in the computer into analog line number, and then transmits it to another telecommunication terminal through the telephone line, and then converts the analog signal into digital signal. The telephone line frequency is not high, and it is usually used for analog signal related work.