This configures whether a DS1 (T1) line interface is set up for short-haul use (intended for intra-building cabling runs) or long-haul use (intended for longer inter-building distances), which determines which of two mutually exclusive tuning parameters applies. Administrators set this based on the actual physical cable run length between the DS1 interface and its far-end connection, since using the wrong setting can cause signal quality or framing errors. For a DS1 circuit run entirely within one building's equipment room, an admin would set this to shortHaul rather than the default longHaul.