A DSL variant that employs ISDN BRI (Basic Rate Interface) technology to deliver symmetric transmission rates of 128 kbps or 144 kbps on unshielded twisted pair (UTP) local loops as long as 18,000 feet. IDSL bonds the two 64-kbps bearer (B) channels to provide a 128-kbps channel, and bonds the 16-kbps data (D) channel to bring the total to 144 kbps. Unlike ISDN, which is a circuit-switched network service for voice, data, fax, video, and multimedia, IDSL operates only at the local loop level to provide always-on Internet access. IDSL is virtually non-existent in the United States, where ISDN never enjoyed any significant success. As IDSL compares so unfavorably with asymmetric digital subscriber line (ADSL) and other DSL variants with respect to bandwidth, the very low IDSL penetration rates will only decrease. See also ADSL, always on, bandwidth, bonding, BRI, circuit switch, Internet, ISDN, local loop, symmetric, transmission rate, UTP, and xDSL.