PCRF Capacity Calculator
Size PCRF/PCF policy nodes from subscriber count, sessions per subscriber and Gx transaction rate with N+1 redundancy.
About PCRF Capacity Calculator
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
Worked example
With the default values below, PCRF Capacity Calculator returns Diameter Transaction Rate of 667. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Subscribers servedaccepts 1–200,000,000 subscribers
- 2,000,000 subscribers
- Policy sessions per subscriberaccepts 0.1–10 sessions
- 1.5 sessions
- Diameter messages per sessionaccepts 1–40 messages
- 4 messages
- Share of sessions established in the busy houraccepts 1–100 %
- 20 %
- Rated capacity per policy nodeaccepts 100–500,000 TPS
- 5,000 TPS
Results
- Diameter Transaction Rate
- 667 TPS
- Policy Nodes Required (N+1)
- 2
- Active Policy Sessions
- 3,000,000
- Utilisation of Deployed Nodes
- 6.7%
Step by step
- 1Values used
- 2PCRF Capacity
- 3Diameter Transaction Rate= 667 TPS
- 4Policy Nodes Required (N+1)= 2
- 5Active Policy Sessions= 3,000,000
- 6Utilisation of Deployed Nodes= 6.7
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
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.