T1 circuits, implemented over twisted-pair copper cables, are still in use today to carry voice channels over relatively short distances (up to 20 or 30 miles). Repeaters (actually, digital regenerators) like this are spaced at 6000-foot intervals, and are usually placed on utility poles or posts. They are a common sight today along suburban streets and country roads.

Each T1 circuit requires two transmission paths, one in each direction. T1 circuits can be implemented over open-wire conductors, twisted-pair copper conductors, coaxial cable, fiber optic cable, microwave links, or satellite links.