Size PCRF/PCF policy nodes from subscriber count, sessions per subscriber and Gx transaction rate with N+1 redundancy.
Each policy session costs a fixed number of Diameter transactions to set up and tear down. Spreading the busy-hour share of those sessions across 3600 seconds gives the sustained transaction rate, which is the figure PCRF platforms are actually rated against. Policy nodes are the choke point during a mass reattach: if the surviving nodes cannot absorb the Gx storm, every data session fails authorisation rather than degrading gracefully.
PCRF Capacity
Gx TPS = (sessions × busy-hour share × messages per session) ÷ 3600; nodes = ceil(TPS ÷ node capacity) + 1 for N+1.
Gx TPS = (sessions × busy-hour share × messages per session) ÷ 3600; nodes = ceil(TPS ÷ node capacity) + 1 for N+1. Each policy session costs a fixed number of Diameter transactions to set up and tear down. Spreading the busy-hour share of those sessions across 3600 seconds gives the sustained transaction rate, which is the figure PCRF platforms are actually rated against.
Policy nodes are the choke point during a mass reattach: if the surviving nodes cannot absorb the Gx storm, every data session fails authorisation rather than degrading gracefully.
This calculator takes 5 inputs: Subscribers served, Policy sessions per subscriber, Diameter messages per session, Share of sessions established in the busy hour, Rated capacity per policy node. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.