PCRF Capacity Calculator
Size PCRF/PCF policy nodes from subscriber count, sessions per subscriber and Gx transaction rate with N+1 redundancy.
Inputs
Diameter Transaction Rate
667TPS
Policy Nodes Required (N+1)
2
Active Policy Sessions
3,000,000
Utilisation of Deployed Nodes
6.7%
Step by step
Values used
Subscribers served = 2,000,000 subscribers; Policy sessions per subscriber = 1.50 sessions; Diameter messages per session = 4 messages; Share of sessions established in the busy hour = 20 %; Rated capacity per policy node = 5,000 TPS
PCRF Capacity
Gx TPS = (sessions × busy-hour share × messages per session) ÷ 3600; nodes = ceil(TPS ÷ node capacity) + 1 for N+1.
Diameter Transaction Rate
= 667 TPS
Policy Nodes Required (N+1)
= 2
Active Policy Sessions
= 3,000,000
Utilisation of Deployed Nodes
= 6.7
How it works
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.
Formula
PCRF Capacity
Gx TPS = (sessions × busy-hour share × messages per session) ÷ 3600; nodes = ceil(TPS ÷ node capacity) + 1 for N+1.
- messages per session
- CCR-I, CCA-I, CCR-T, CCA-T and any mid-session RAR/RAA
- N+1
- One spare node so a failure does not breach capacity
Frequently Asked Questions
How is PCRF Capacity calculated?
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.
Why does PCRF Capacity matter?
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.
What values do I need to enter?
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.