# Token-bucket sustained burst · example 3

Subject: Computer Networks

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/cn/#tee/practice/congestion/token-burst-3

Canonical: https://deep-learning-study-room.vercel.app/read/cn/tee/practice/congestion--token-burst-3/

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 16000 byte-tokens, replenishes at 4000 bytes/s, and transmits continuously at peak 8000 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=16000 bytes; r=4000 B/s; P=8000 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

8000−4000=4000 tokens/s.

#### Step 2. Time to exhaust B

t=16000/4000=4 s.

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

D=8000×4=32000 bytes. Check B+rt=16000+4000×4=32000 bytes.

**Final answer:** Peak burst lasts 4 s and sends 32000 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.