# Token-bucket sustained burst · example 1

Subject: Computer Networks

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/cn/#tee/practice/congestion/token-burst-1

Canonical: https://deep-learning-study-room.vercel.app/read/cn/tee/practice/congestion--token-burst-1/

Optional extension · no matching calculation in the two supplied papers

**Optional worked extension.** This calculation format was not found in the supplied December 2025 final or February 2026 re-exam. The numbers and practice marks are authored. Study the core concept and actual-paper questions first; this is extra explanation, not a TEE prediction.

### Practice question. A token bucket starts full with 10000 byte-tokens, replenishes at 2000 bytes/s, and transmits continuously at peak 12000 bytes/s while tokens permit. Under a fluid model with P>r, find the maximum peak-rate burst duration and data sent. [7 practice marks]

#### Answer

## Given

B=10000 bytes; r=2000 B/s; P=12000 B/s; continuously backlogged fluid traffic.

## To find

Time until tokens exhaust and bytes sent at the peak rate.

## Formula and why



$$
t=\frac{B}{P-r},\quad D=Pt
$$



Tokens are consumed at P and simultaneously replenished at r, so net depletion is P−r.

## Step-by-step solution

#### Step 1. Net depletion

12000−2000=10000 tokens/s.

#### Step 2. Time to exhaust B

t=10000/10000=1 s.

#### Step 3. Data sent and independent balance

D=12000×1=12000 bytes. Check B+rt=10000+2000×1=12000 bytes.

**Final answer:** Peak burst lasts 1 s and sends 12000 bytes.

#### What this result means

Using B/P would ignore replenishment during transmission. Packetized scheduling may round timing; this question explicitly uses a fluid model.