1. Telephone lines, suitable for telecommunication engineering wiring, connection between indoor telephone communication cable system wiring, backbone lines between voice communication systems, program-controlled switches, telephones, fax and digital telephones.

2. Twisted pair uses a pair of mutually insulated metal wires to twist each other to resist some external electromagnetic wave interference. Twisting two insulated copper wires to each other at a certain density can reduce the degree of signal interference. The radio waves radiated by each wire during transmission will be cancelled by the radio waves emitted by the other wire. The name "twisted pair" also came from this. Twisted-pair wires are generally made of two 22-26 insulated copper wires intertwined with each other. In actual use, twisted-pair wires are wrapped by multiple pairs of twisted wires in an insulated cable sleeve. There are four pairs of typical twisted pairs, and many more twisted pairs are placed in a cable sleeve.