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Exam 300-420 topic 1 question 189 discussion

Actual exam question from Cisco's 300-420

Question #: 189
Topic #: 1

Since installing a cisco TelePresence system, the company is experiencing other application having response issues when the system in use. As a result, the company asked an architect to recommend a QoS solution. The customer is currently using a CBWFQ policy to manage traffic on an internet connection with a speed of 100 Mbps. Which link-capacity limit must the architect choose for strict-priority for the real-time traffic?

A. 25 Mbps
B. 50 Mbps
C. 33 Mbps
D. 75 Mbps

Show Suggested Answer

Suggested Answer: C 🗳️

by Hope66 at Sept. 24, 2022, 8:11 a.m.

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beskar

1 year, 4 months ago

Selected Answer: C

For an 8 queue CBWFQ w/LLQ, Voice w/EF = 10%, Multimedia Conferencing w/CS4 = 23%. Both of these are to be placed in the strict-priority queue. Answer = 33% total for strict-priority queue.

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SpicyMochi

1 year, 8 months ago

Selected Answer: C

The recommended link-capacity limit for strict-priority real-time traffic in a QoS solution is typically one-third (33%) of the available bandwidth. This is because allocating too much bandwidth to real-time traffic could lead to congestion for other types of traffic. In this case, the internet connection has a speed of 100 Mbps, so the architect should choose: C. 33 Mbps

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cerifyme85

1 year, 8 months ago

https://www.ciscopress.com/articles/article.asp?p=2756478&seqNum=8#:~:text=the%20networking%20team.-,8%2DClass%20QoS%20Strategy,queue%2C%20and%20other%20traffic%20types%2C%20such%20as%20multimedia%20streaming%2C%20have%20guaranteed,-provisioned%20bandwidth.

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neiker45

1 year ago

This is a really good link to learn about this.

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cerifyme85

1 year, 8 months ago

Selected Answer: C

javascript:popUp('/content/images/chap16_9781587144622/elementLinks/16fig06_alt.jpg')

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andrewChan

2 years, 2 months ago

Selected Answer: C

D is not correct https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/qos_conmgt/configuration/xe-3s/qos-conmgt-xe-3s-book/qos-conmgt-oview.html#GUID-48F6AF58-5CCC-44A0-B868-125AE453FF2A%20%20%20%20%20%20(75%20Mbps) The sum of all bandwidth allocation on an interface cannot exceed 75 percent of the total available interface bandwidth. The remaining 25 percent is used for other overhead, including Layer 2 overhead, routing traffic, and best-effort traffic. Bandwidth for the CBWFQ class-default class, for instance, is taken from the remaining 25 percent. above meaning is in the CBWFQ, total bandwidth of class-map assigned into the policy-map must not be over 75% of total bandwidth of the link

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andrewChan

2 years, 2 months ago

C should be correct https://www.ciscopress.com/articles/article.asp?p=357102&seqNum=7 This strict-priority queuing rule (limit to 33 percent) is simply a best-practice design recommendation; it is not a mandate. In some cases, specific business objectives cannot be met while holding to this recommendation. In such cases, enterprises must provision according to their detailed requirements and constraints. However, it is important to recognize the trade-offs involved with overprovisioning strict-priority traffic with respect to the negative performance impact on response times in non-real-time applications. BTW, strict-priority queue or formal called LLQ is an add-on to CBWFQ, for real-time, delay sensitive traffic.

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ciscoman8

2 years, 2 months ago

C. https://www.ciscopress.com/articles/article.asp?p=357102&seqNum=7 Cisco Technical Marketing testing has shown a significant decrease in data application response times when real-time traffic exceeds one-third of a link's bandwidth capacity. Extensive testing and customer deployments have shown that a general best queuing practice is to limit the amount of strict-priority queuing to 33 percent of a link's capacity. This strict-priority queuing rule is a conservative and safe design ratio for merging real-time applications with data applications.

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Hope66

2 years, 3 months ago

I think D: find CBWFQ bandwidth allocation https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/qos_conmgt/configuration/xe-3s/qos-conmgt-xe-3s-book/qos-conmgt-oview.html#GUID-48F6AF58-5CCC-44A0-B868-125AE453FF2A%20%20%20%20%20%20(75%20Mbps)

upvoted 4 times

johnu329

2 years, 2 months ago

In your link, I found the following statements. "The sum of all bandwidth allocation on an interface cannot exceed 75 percent of the total available interface bandwidth." --> This may suggest 75 Mbps is correct. "...it is possible to enqueue various types of real-time traffic to the strict priority queue, we strongly recommend that you direct only voice traffic to it because voice traffic is well-behaved, whereas other types of real-time traffic are not." --> In our question, they are talking about all real-time traffic considered strict-priority. However, that recommendation suggest to only consider voice traffic as strict-priority. I am uncertain...

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