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Difficulty: MediumQoS Per-Hop Behaviors, Classification, Marking, Queuing, and Traffic Shaping/Policing

An enterprise WAN link connects a remote branch office to the primary data center over a service provider connection with a contracted Committed Information Rate (CIR) of 10 Mbps10\text{ Mbps}. The service provider immediately drops any bursts that exceed 10 Mbps10\text{ Mbps} at the ingress port of the provider edge router. To prevent packet drops during short bursts by queuing excess packets in memory and releasing them at a controlled rate, which Quality of Service (QoS) mechanism should be applied to the enterprise egress router interface?

  1. Traffic shapingAnswer
  2. B
    Traffic policing
  3. C
    Layer 2 Class of Service (CoS) PCP marking
  4. D
    Differentiated Services Code Point (DSCP) remarking

Answer

Traffic shaping
Traffic shaping uses internal memory buffers to store packets that exceed the configured bandwidth limit (such as a 10 Mbps10\text{ Mbps} CIR) during burst periods. It then releases the queued packets onto the physical link at a steady, controlled rate, preventing packet drops at downstream provider interfaces that strictly enforce rate limits.

Step-by-Step Solution

1
Analyze the operational requirements of the WAN interface scenario.
The service provider enforces a strict limit (10 Mbps10\text{ Mbps}) and drops micro-bursts that exceed the CIR.
Enterprise traffic exceeding the contracted threshold gets dropped at the provider edge unless smoothed prior to egress.
2
Compare traffic conditioning mechanisms (policing vs. shaping).
Traffic policing discards out-of-profile packets or remarks them; traffic shaping buffers excess traffic and queues it for delayed transmission.
Buffering smoothed traffic prevents packet drops at the provider edge during brief micro-bursts.
3
Select the mechanism that buffers excess traffic for egress transmission.
Traffic shaping is the correct mechanism.
It aligns egress transmission rates with the contracted provider rate via packet buffering.

Key Concept

Traffic Shaping vs. Traffic Policing Mechanisms
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Topics

QoS Per-Hop Behaviors, Classification, Marking, Queuing, and Traffic Shaping/Policing

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