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QID:BCM226, this one is weird
#1
???

Which three QoS mechanisms can be configured to improve VoIP quality on a converged network?

1. The use of WRED
2. The proper classification and marking of the traffic as close to the source as possible
3. The use of RTP header compression for the VoIP traffic
4. The use of a queuing method that will give VoIP traffic strict priority over other traffic.
5. (bogus line)

I chose the 124, the answer says 123. The next time I chose 123, the answer says 124. Either way, I was wrong?!

And the funny thing is, the explanation says all 4 are correct.

Anyone? I am taking a test tomorrow and this is not what I want to take with me to the test.
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#2
I am sorry but your whole story is wrong.
I tried this question in online test and given below is what I got. When I selected these given answers, my answer was marked correct. Moreover, please read complete explanation; it says WRED is not chosen as correct answer and also gives its reason. Please give proper attention to each question.

You can directly access any question using its QID (like BCM226 in this case) in the Question Search field on the test index page.

(QID:BCM226) Which three QoS mechanisms can be configured to improve VoIP quality on a converged network?

A. The use of a queuing method that will give VoIP traffic strict priority over other traffic.
B. The use of RTP header compression for the VoIP traffic.
C. The proper classification and marking of the traffic as close to the source as possible.
D. The use of 802.1QinQ trunking for VoIP traffic.
E. The use of WRED.

Correct Answer:

The use of a queuing method that will give VoIP traffic strict priority over other traffic.
The use of RTP header compression for the VoIP traffic.
The proper classification and marking of the traffic as close to the source as possible.

Explanation:

In order to optimize the quality of VOIP calls, QoS should be implemented to ensure that VOIP traffic is prioritized over other traffic types. By providing a strict queue for VOIP traffic, you will ensure that voice calls take precedence over the other traffic types.

In order to properly provide for QoS across the network, the voice traffic should be marked to give priority as close to the source as possible. This will ensure that the traffic is prioritized end to end.

RTP header compression is used to compress UDP and RTP headers, thus lowering the delay for transporting real-time data, such as voice and video over slower links.

Weighted Random Early Detection (WRED) is a congestion avoidance mechanism that randomly drops packets with a certain IP precedence when the buffers are reaching a defined threshold. WRED is a combination of two features: tail drop and random early detection (RED). We are eliminating this answer because RED is not precedence- or CoS-aware. RED and WRED are very useful congestion avoidance mechanisms when the traffic type is TCP-based. For other types of traffic, RED is not very efficient.

Building Cisco Multilayer Switched Networks (BCMSN) v2.1, Cisco Systems 2004, Chapter 8.
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#3
My mistake. Thank you for the explanation!
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#4
Admin,

I disagree. I believe the answers should be;

A. The use of a queuing method that will give VoIP traffic strict priority over other traffic.
C. The proper classification and marking of the traffic as close to the source as possible.
E. The use of WRED.


B. The use of RTP header compression for the VoIP traffic.

This does not improve the VoIP quality, in fact compression of any kind will never improve the VoIP quality compared to it original format.

Had the question asked on methods that reduces bandwidth utilisation from VoIP, then yes I would agree, but the question is asking about VoIP quality and I believe this is wrong as RTP header compression will reduce the quality of the VoIP call when measured correctly against it uncompressed counterparts.

Please let me know what your thoughts are on this
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