This is the upper threshold for ISR sessions. This attribute and the
following one control the node's ISR congestion status. The node
state changes from uncongested to congested if the number of ISR
sessions exceeds the upper threshold. The node state changes back
to uncongested once the number of ISR sessions dips below the
lower threshold. To prevent thrashing, the lower threshold should be
less than the upper threshold. The upper threshold should be lower
than maximumIsrSessions.