This read-only value is the subslot index component of the composite index identifying a FlexE subslot entry, corresponding to the specific subslot within a slot. An admin uses it alongside the frame and slot indices to identify exactly which subslot's FlexE sub-time-slot granularity is being reported or configured. For example, a value of 0 might identify the first, or only, subslot on a card that doesn't have multiple physical subslots.