This enables or disables transmission of Performance Report Messages (PRM) on this DS1 port's ESF Facility Data Link. PRM messages carry this specific port's own performance statistics to the far end over the FDL, so enabling this is what lets a remote carrier or peer network element monitor this circuit's health without needing separate out-of-band access to this switch. A carrier SLA requiring visibility into near-end performance on a leased circuit would depend on this being enabled on this port so PRM messages actually reach their monitoring equipment.