This read-only Unsigned32 gives the History time-stamp for this row of the msdp directional (Tx/Rx) history table, expressed as UTC seconds elapsed since midnight, January 1st 1970. Because the switch stores a rolling history of samples rather than only the current value, an admin needs this index to know exactly when the counters in that particular row of the msdp directional (Tx/Rx) history table were captured. An admin comparing two rows of the msdp directional (Tx/Rx) history table would use msdpTimeStampIndex to confirm one sample was taken, say, an hour before the other, before concluding traffic had actually grown between them.