Work out how many subscribers a cluster of core nodes supports, with redundancy reserved and headroom against today's load.
Core nodes are licensed in sessions, not subscribers, and a modern handset holds more than one session at a time. Reserving a node for failover means the cluster's advertised capacity is deliberately lower than the sum of its parts. Sizing to the full cluster total is the classic mistake: the day one node fails, the remaining nodes reject sessions and the outage becomes a capacity incident rather than a redundancy event.
Subscriber Capacity
supported subscribers = (effective nodes × sessions per node) ÷ sessions per subscriber, where N+1 removes one node from the total.
supported subscribers = (effective nodes × sessions per node) ÷ sessions per subscriber, where N+1 removes one node from the total. Core nodes are licensed in sessions, not subscribers, and a modern handset holds more than one session at a time. Reserving a node for failover means the cluster's advertised capacity is deliberately lower than the sum of its parts.
Sizing to the full cluster total is the classic mistake: the day one node fails, the remaining nodes reject sessions and the outage becomes a capacity incident rather than a redundancy event.
This calculator takes 5 inputs: Deployed nodes, Session capacity per node, Average sessions per subscriber, Reserve one node for failover (N+1), Subscribers today. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.