The telephone line is the incoming line of the telephone, which can only be connected to the telephone. It is divided into 2 cores and 4 cores. There are three kinds of conductor materials: copper clad steel, copper clad aluminum and all copper. All copper has the best conductor effect. Telephone line shall be used for communication engineering wiring, connection between indoor telephone communication cable system wiring, trunk line between voice communication systems, program-controlled switch, telephone.

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.