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352-001 · Question #603

How must queue sizes be designed to ensure that an application functions correctly?

The correct answer is D. The sum of the queuing delay of all devices in chain must be less than or equal to the application. End-to-end application performance depends on the cumulative queuing delay across all devices in the forwarding path, not on any single device in isolation.

Design Considerations

Question

How must queue sizes be designed to ensure that an application functions correctly?

Options

  • AThe default queue sizes are good for any deployment
  • BEach individual device queuing delay in chain must be less than or equal to the application
  • CThe queuing delay on every device in chain must be exactly the same
  • DThe sum of the queuing delay of all devices in chain must be less than or equal to the application

How the community answered

(39 responses)
  • A
    3% (1)
  • B
    15% (6)
  • C
    10% (4)
  • D
    72% (28)

Why each option

End-to-end application performance depends on the cumulative queuing delay across all devices in the forwarding path, not on any single device in isolation.

AThe default queue sizes are good for any deployment

Default queue sizes are not universally appropriate because they do not account for specific application delay tolerances, traffic rates, or packet sizes in a given deployment.

BEach individual device queuing delay in chain must be less than or equal to the application

Requiring each individual device delay to be within the application's full tolerance is unnecessarily restrictive and ignores that end-to-end delay is the sum of all per-hop delays.

CThe queuing delay on every device in chain must be exactly the same

Equal queuing delay on every device is an arbitrary constraint that does not ensure the total end-to-end delay remains within the application's tolerance.

DThe sum of the queuing delay of all devices in chain must be less than or equal to the applicationCorrect

Each device in the forwarding chain contributes a portion of the total end-to-end delay experienced by application traffic. The aggregate sum of all per-device queuing delays must be less than or equal to the application's maximum tolerable delay budget to ensure correct operation.

Concept tested: End-to-end QoS queuing delay budget design

Source: https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoS-SRND-Book/QoSDesign.html

Topics

#QoS#queuing delay#queue sizing#application latency

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