Remote concentrator

In North America concentrators are located in a serving area interface (SAI) or other enclosure in each neighborhood.

In Europe the buildings which once contained local Strowger switch telephone exchanges are now usually empty except for a remote concentrator.

The central switch periodically counts concentrators, and schedules maintenance, probably before users notice the failure.

For example, a fiber optic cable might run up to 30 kilometres (19 mi) without a repeater from the telephone exchange to a concentrator site, and local subscriber wire local loops can extend an additional 4 km beyond the concentrator and its DSLAM.

With repeaters in the fiber optic cable the distance from the telephone exchange can be extended much farther.