This 64-bit counter tallies packets with CRC errors received from the physical SRP ring fiber, counted over the current, still-running 15-minute window. This is the same class of line-noise/fiber-degradation signal as the RxErrorsCRC counters elsewhere in this MIB, and because it's tracked in this separate error-count group as well, comparing the two over the same interval is a useful sanity check that both counting paths agree on the scale of the problem. A fiber segment with a marginal connector might show a slow, steady climb in this counter of a few errors per interval rather than a sudden jump, which is the pattern typical of degrading (rather than freshly broken) optics.