A value which uniquely identifies this conceptual
row in the ctTrunkConfigTable. The Table allows sparse values.
If the conceptual row identified by this value of
ctTrunkIndex is recreated following an agent restart,
the same value of ctTrunkIndex must be used to identify
the recreated row. (However, the Interfaces table
index associated with the client may change. ifAlias in ifXTable is used
then to reassociate ifIndexes based on ifAlias. In the case of the SSR,
Smart Trunks are manipulated as st.ctTrunkIndex