Hi,
you can add two pools of controller for fail over. Most WiNG installation use just one pool.
The level is for MINT links. You can see it as routing, level 1 for local deployments and level 2 for NOC deployments with different RF domains.
Pool1=1-NX-1>,1-NX-2>;Pool2=2-NX-1>,2-NX-2>;level=1|2