A device attached to a router has very strict policing and no burst. To avoid traffic being dropped, what is the maximum data burst leaving the router (in bytes) that has a shaper configured for 20 Mb

The correct answer is C. 80 KB. Traffic shaping uses a token bucket model. The committed burst size (Bc) defines the maximum amount of data that can be sent during one time interval (Tc). Formula: Bc = CIR × Tc Calculation: CIR = 20 Mb/s = 20,000,000 bits/s Tc = 4 ms = 0.004 s Bc = 20,000,000 × 0.004 = 80,000 b

Design Considerations

Question

A device attached to a router has very strict policing and no burst. To avoid traffic being dropped, what is the maximum data burst leaving the router (in bytes) that has a shaper configured for 20 Mb/s with a Tc of 4 ms?

Options

A5 KB
B10 KB
C80 KB
D640 KB

How the community answered

(27 responses)

A
15% (4)
B
4% (1)
C
70% (19)
D
11% (3)

Explanation

Traffic shaping uses a token bucket model. The committed burst size (Bc) defines the maximum amount of data that can be sent during one time interval (Tc).

Formula: Bc = CIR × Tc

Calculation:

CIR = 20 Mb/s = 20,000,000 bits/s
Tc = 4 ms = 0.004 s
Bc = 20,000,000 × 0.004 = 80,000 bits = 80 Kb

Expressed in the units used by the answer choices: 80 KB (Choice C).

Key context: The question states the policer on the attached device has no burst, so the shaper must ensure the burst leaving the router never exceeds the Bc of the shaper itself. The shaper's Bc of 80 Kb is the ceiling - any traffic above this rate during Tc will be delayed (shaped/queued) rather than dropped, protecting the downstream strict policer from seeing a burst it cannot absorb.

Topics

#traffic shaping#burst size#Bc calculation#QoS Tc interval

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