csOc3InvalidIntervals is a read-only count of how many of the previous 15-minute intervals for this OC3 port have no usable performance data. A nonzero value flags a data-collection gap in the management agent itself rather than necessarily a real fault on the fiber, which matters when an admin is deciding whether an apparently clean history window is genuinely clean or just missing data. For example, if csOc3InvalidIntervals jumps to 4 right after a management-card failover, an admin knows those four 15-minute buckets of OC3 history are unreliable rather than concluding the port had a perfectly quiet hour.