This PmProfileFieldMapBasicPtp field is a bitmap indicating which specific fields within this Basic PTP history profile the device has declared unsupported for this particular timing session or hardware. Because this row is a closed, completed interval from the PTP performance-monitoring history table for this timing session, any bit set here means the corresponding counter or measurement elsewhere in this same row was never actually collected by this hardware/firmware combination, so it should be ignored rather than read as a real zero or low value. For example, if the bit for the optical-power field is set here, an OprOch value of 0 in the same row does not mean zero optical power was measured — it means the device could not measure it at all on this port.