This object contains an appropriate value to be used for
tAtmTdpIndex when creating entries in the tAtmTdpTable.
The value 0 indicates that no unassigned entries are
available. To obtain the tAtmTdpIndex value for a new
entry, the manager issues a management protocol
retrieval operation to obtain the current value of this
object. After each retrieval, the agent should modify the
value to the next unassigned index.
After a manager retrieves a value the agent will determine
through its local policy when this index value will be made
available for reuse.