# Q7B · Traffic-shaping algorithm

Subject: Computer Networks

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/cn/#tee/mocks/tee-mock-b/q7b

Canonical: https://deep-learning-study-room.vercel.app/read/cn/tee/mocks/tee-mock-b--q7b/

TEE · 100 attempted marks · solutions for every choice · current syllabus 702AI0C023

### TEE practice mock · Q7B. Draw and explain the leaky-bucket algorithm. Is it always better than a token bucket? [10 mock marks]

#### Answer

In the textbook **leaky-bucket queue/shaper** model, arriving packets enter a finite buffer. The output sends at a configured rate whenever data is queued. When the queue empties, it cannot send nonexistent packets; when the buffer is full, excess arrivals are dropped in this finite-buffer model.

Swipe across the diagram to read its labels ↔

![Leaky-bucket data queue](https://deep-learning-study-room.vercel.app/cn/fig/tee-leaky.77bdbcf957.svg)

Diagram: Leaky-bucket data queue. Labels: Leaky-bucket data queue | Leaky-bucket data queue | Bursty arrivals enter finite buffer B | Accept packets that fit; the stated queue model drops overflow. | Queue drains at configured rate r | Send while data exists. An empty queue produces no packets. | Smoother departure stream | Buffering adds delay; idle service cannot be saved for a later burst.

Finite data buffer smooths a burst into a bounded departure rate.

1. Choose buffer capacity B and output service rate r in consistent units.
2. Admit arrivals that fit. Drop/mark overflow according to the stated implementation; this queue example drops the excess.
3. Drain at rate r while the queue is nonempty. Idle time does not accumulate permission for a later faster burst.
4. The result is smoothed output. Larger buffers accommodate larger bursts but can increase waiting delay.

| Advantage | Limitation |
| --- | --- |
| Simple bound on output rate | Bursts may overflow or suffer delay |
| Reduces short-term output variation | Unused idle service cannot be saved |
| Useful for predictable traffic shaping | No end-to-end delay/loss guarantee by itself |

The term “leaky bucket” can also describe a conformance meter in standards. This course’s diagrams and numerical questions explicitly use the finite data-queue model, so its state is queued data rather than tokens.

#### Practical example

A queue of 20 packets drained at 5 packets/s needs 4 seconds to empty without new arrivals. If it is already full, an instantaneous extra burst cannot all be stored.

No algorithm is universally better. The leaky data-queue model is useful for a smooth output profile; token bucket is preferable when controlled bursts should be allowed. State the application’s delay, burst and rate needs before recommending one.