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DescriptionQ1083

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Q1083DVASIC interview problem

Model a token bucket with one-time aging bypass

TechniquesPythonToken bucketRate limitingAging

DifficultyHard

TopicReference Models

LanguagePython

Requirements4 checkpoints

Problem

Implement a token-bucket checker with capacity 16, four new tokens every ten cycles, one token consumed per send, and one no-token bypass for a packet that has waited more than twenty cycles.

Example input and output

Use this case to check your interpretation

Input

at cycle 21: tokens=0, packet id=9 has waited since cycle 0 after intervening legal sends consumed refills; send id9 twice

Output

first send uses its one aging bypass and removes id9; second send is rejected as unknown/duplicate

Explanation

Age 21 is greater than twenty and no token exists, so exactly one bypass is legal; successful removal prevents replay.

Requirements (4)

Apply every elapsed refill interval, cap the bucket at 16, and preserve the ten-cycle refill phase.
Track enqueue time by packet ID and reject sends for packets that were never enqueued.
Permit a bypass only when no token exists, age is greater than 20, and that packet has never bypassed.
Remove successful packets from the wait table and reject duplicate sends.