Discuss CWNP CWNA-109 Exam Topic 1 Question 39

A dual-band 802.11ac AP must be powered by PoE. As a class 4 device, what power level should be received at the AP?

A30 W

B12.95 W

C25.5 W

D15.4 W

Suggested Answer: C

PoE has different standards that define different power levels for PSEs and PDs. The original standard, IEEE 802.3af, defines two classes of PSEs: Class 3 (15.4 W) and Class 4 (30 W). The newer standard, IEEE 802.3at, also known as PoE+, defines four classes of PSEs: Class 0 (15.4 W), Class 1 (4 W), Class 2 (7 W), and Class 3 (12.95 W). The power level received at the PD is always lower than the power level provided by the PSE, due to cable resistance and power dissipation. The IEEE standards specify the minimum power level that must be received at the PD for each class of PSE.For a Class 4 PSE, the minimum power level received at the PD is 25.5 W910.Reference:CWNA-109 Study Guide, Chapter 7: Power over Ethernet (PoE), page 295;CWNA-109 Study Guide, Chapter 7: Power over Ethernet (PoE), page 289.

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20 comments · newest first

Jerry 1 month ago

Definitely 30 W. We need headroom for peak usage.

Nan 2 months ago

25.5 W is the sweet spot for performance.

Marti 2 months ago

I agree, 15.4 W is too low for a class 4 device.

Sylvie 2 months ago

12.95 W doesn’t seem sufficient for an AP.

Dell 2 months ago

I’m leaning towards 25.5 W. Feels right for dual-band.

Tawanna 2 months ago

I think it should be 30 W. Seems like enough power.

Dorsey 2 months ago

Yeah, class 4 is all about that 30 W power!

Sarina 3 months ago

Wait, are we sure about that? Seems high!

Donte 3 months ago

I thought it was 15.4 W, but I guess not?

Malcom 3 months ago

Definitely C, 25.5 W is the right answer!

Brice 3 months ago

It should be 30 W for class 4.

Paola 3 months ago

Yeah, 30 W makes sense for dual-band APs!

Tess 3 months ago

Wait, 30 W? Really? That’s higher than I expected!

Franchesca 4 months ago

I thought it was 15.4 W? Seems off.

Annette 5 months ago

Definitely 25.5 W, that’s the right power level.

Rene 5 months ago

It should be 30 W for class 4.

Jade 6 months ago

I believe it’s 30 W, but I might be mixing it up with another class. I need to double-check!

Brandon 6 months ago

I’m a bit confused; I thought class 4 was 15.4 W, but that seems too low for a dual-band AP.

Raylene 6 months ago

I remember practicing a similar question, and I think the answer was 25.5 W for class 4 devices.

Karan 6 months ago

I think a class 4 device like this AP should receive around 30 W, but I'm not entirely sure.

CWNP CWNA-109 Exam - Topic 1 Question 39 Discussion