This chooses whether the OAM loopback test cell is echoed back by the nearest ATM segment endpoint (segment) or travels all the way to the far Cascade device and back (end-to-end), which determines how much of the circuit's path the test actually validates. An admin doing initial fault isolation on a long multi-hop circuit would start with segment loopbacks hop by hop before escalating to an end-to-end test. For example, a segment loopback that succeeds at every intermediate hop but an end-to-end test that still fails would point to a problem specifically at the final destination endpoint rather than anywhere along the intermediate path.