Traffic Burst Calculator
Size a token bucket: the committed burst size a policer needs to pass a burst without dropping it.
Inputs
Committed Burst Size Required
5 MiB
Burst The Configured CBS Allows
1.111ms
Bytes Sent During The Burst
6 MiB
Bytes Covered By The CIR
610 KiB
Verdict
Exceeding — tokens run out and packets drop
Step by step
Values used
Committed information rate (CIR) = 100 Mbit/s; Peak burst rate = 1,000 Mbit/s; Configured committed burst size = 125,000 bytes; Burst duration = 50 ms
Traffic Burst
CBS = (peak rate − CIR) × burst duration ÷ 8, the excess bytes the bucket must hold.
Maximum conforming burst
burst the bucket allows = CBS × 8 ÷ (peak rate − CIR)
Committed Burst Size Required
= 5,625,000
Burst The Configured CBS Allows
= 1.111 ms
Bytes Sent During The Burst
= 6,250,000
Bytes Covered By The CIR
= 625,000
Verdict
= Exceeding — tokens run out and packets drop
How it works
A token bucket refills at the CIR and empties at the sending rate, so only the difference between the two drains it. The burst a given bucket tolerates is its depth divided by that drain rate; sizing the bucket the other way round gives the depth a known burst needs. Policers configured with a default CBS drop the first few milliseconds of every TCP transfer, which triggers retransmits and makes a link that is nowhere near capacity feel broken.
Formulas
Traffic Burst
CBS = (peak rate − CIR) × burst duration ÷ 8, the excess bytes the bucket must hold.
- CIR
- Committed information rate the bucket refills at
- peak rate
- Rate the source actually bursts at
- CBS
- Committed burst size in bytes
Maximum conforming burst
burst the bucket allows = CBS × 8 ÷ (peak rate − CIR)
- CBS
- Configured bucket depth in bytes
- peak rate − CIR
- Rate at which tokens are drained faster than they refill
Frequently Asked Questions
How is Traffic Burst calculated?
CBS = (peak rate − CIR) × burst duration ÷ 8, the excess bytes the bucket must hold. A token bucket refills at the CIR and empties at the sending rate, so only the difference between the two drains it. The burst a given bucket tolerates is its depth divided by that drain rate; sizing the bucket the other way round gives the depth a known burst needs.
Why does Traffic Burst matter?
Policers configured with a default CBS drop the first few milliseconds of every TCP transfer, which triggers retransmits and makes a link that is nowhere near capacity feel broken.
What values do I need to enter?
This calculator takes 4 inputs: Committed information rate (CIR), Peak burst rate, Configured committed burst size, Burst duration. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.