This object is a unique per-interface index number, from 1 to N, distinguishing this particular threshold-crossing-alert entry among the multiple TCAs that can be configured for the same interface identified by tcaIfIndex. Admins use it together with tcaIfIndex to uniquely address one TCA row, since a single interface can have several independent threshold counters being watched. For example, an interface might have tcaIndex values 1 through 4 tracking four different counters such as DS1 coding violations and DS3 errors, each in its own row.