Shaping And Policing Rate Calculator

Work out shaping and policing rate instantly with clear inputs, formula shown and shareable results.

About Shaping And Policing Rate Calculator

Shaping buffers traffic above the committed rate and releases it later, converting excess into delay; policing discards or remarks it, converting excess into loss. Burst size is the committed rate multiplied by the tolerance window, and it must be at least a few round trips' worth of data or TCP will be penalised for its normal ramp-up behaviour.

Formula

Shaping and policing

burst bytes = CIR x tolerance / 8; excess = offered - CIR; shaping delay = burst bits / CIR

Worked example

With the default values below, Shaping And Policing Rate Calculator returns Burst size for the committed rate of 610.35 KiB. Change any input above and every figure here is recalculated in your browser.

Inputs used

Committed information rateminimum 0.001 Mbps: 50 Mbps
Burst toleranceminimum 1 ms: 100 ms
Offered traffic rateminimum 0.001 Mbps: 80 Mbps
Enforcement actionone of Shape - queue excess traffic, Police - drop excess traffic, Police - remark excess traffic: Shape - queue excess traffic

Results

Burst size for the committed rate: 610.35 KiB
Excess above the committed rate: 30.00 Mbps
Share of traffic conforming: 62.50%
Enforcement outcome: Excess queued, adding up to 100 ms of delay

Step by step

1Values used
2Shaping and policing
3Burst size for the committed rate= 625,000
4Excess above the committed rate= 30.00 Mbps
5Share of traffic conforming= 62.50
6Enforcement outcome= Excess queued, adding up to 100 ms of delay

Assumptions and limits

The result is derived only from the 4 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 2 decimal places, 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

Should I shape or police?

Shape outbound traffic you control, so TCP sees delay and backs off gracefully. Police inbound traffic you cannot shape, accepting that drops will trigger retransmission.

Why does a small burst size hurt TCP?

Slow start deliberately sends bursts. A tight policer drops them, TCP interprets that as congestion and collapses its window, so measured throughput falls far below the committed rate.