352-001 · Question #118
What is a key design aspect to be considered when designing an IP network that will be carrying real-time VoIP traffic?
The correct answer is D. Minimizing total unidirectional end-to-end delay to 0-150 ms. VoIP quality is governed by ITU-T G.114, which defines the acceptable one-way (unidirectional) end-to-end delay budget as 0 to 150 ms.
Question
What is a key design aspect to be considered when designing an IP network that will be carrying real-time VoIP traffic?
Options
- AMinimizing total bidirectional end-to-end delay to 0-150 ms
- BMinimizing total unidirectional end-to-end delay to 150-500 ms
- CMinimizing total bidirectional end-to-end delay to 0-50 ms
- DMinimizing total unidirectional end-to-end delay to 0-150 ms
How the community answered
(31 responses)- B6% (2)
- C3% (1)
- D90% (28)
Why each option
VoIP quality is governed by ITU-T G.114, which defines the acceptable one-way (unidirectional) end-to-end delay budget as 0 to 150 ms.
Bidirectional delay is not the correct measurement unit in ITU-T G.114; the standard measures one-way delay, and 0-150 ms bidirectional would be an impossibly strict and non-standard requirement.
While the direction (unidirectional) is correct, a range of 150-500 ms exceeds the G.114 maximum threshold of 150 ms for acceptable voice quality.
A 0-50 ms bidirectional target uses the wrong direction metric and is more stringent than any recognized VoIP delay standard.
ITU-T G.114 specifies a maximum one-way delay of 150 ms for good voice quality, with anything above 150 ms and up to 400 ms being acceptable but noticeable. The measurement is unidirectional because each direction of a voice call traverses the network independently, and the standard evaluates each direction separately.
Concept tested: VoIP unidirectional delay requirements per ITU-T G.114
Source: https://www.cisco.com/c/en/us/support/docs/voice/voice-quality/14036-qos-voip.html
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