The RJ-45 is a single-line jack for digital transmission over ordinary phone wire, either untwisted or twisted. It is the interface for Ethernet standards 10BASE-T and 100BASE-T. For faster transmissions in which you're connecting to an Ethernet 10BASE-T network, you need to use twisted pair wire. Untwisted is usually a flat wire like common household phone extension wire. It is also used to connect ISDN terminal equipment to Kaba Benzing terminals.