N+1
From TBwiki
The N+1 solution will allow the customer to achieve five 9 up time for up to 15 TMG7800-STM1. This solution will maintain the exceptional TMG7800-STM1 performance at 2016 channels per unit.
The Stand-by unit being a hot Stand-by, the system will allow the switchover without any human intervention. The N+1 solution will identify the unit to be replaced and reroute automatically the traffic to the Stand-by unit through the Active Patch Panel.