csOc3LineIntervalValidData is a read-only TruthValue flag that says whether the performance counters recorded in this particular 15-minute historical bucket of the SONET/SDH Line performance table on this OC3 port (csOc3LineIntervalTable) are trustworthy or not. Admins need to check this flag before trusting the paired error counters for that interval, since a false value means the agent could not reliably collect data for that period (for example, because the interface only came online partway through it, or the agent was a proxy that lost contact). For example, before flagging a spike found in bucket 7 of the SONET/SDH Line performance table on this OC3 port (csOc3LineIntervalTable) as a real fault, an engineer first confirms the matching csOc3LineIntervalValidData value is true, so a temporarily-unreachable agent doesn't get misread as a live error burst.