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802.11n LWAP 'draws low power' ??

with_joerg
Level 1
Level 1

Dear all,

we deployed the first 802.11n LWAPs. In some areas where the have anumber of clients associated we get the following alarm:

"Access point 'AP001d.70fa.6128' associated with controller 'Cisco_df:f8:e3' draws low power from Ethernet. Failure reason: 'The AP draws 15.4 watts from Ethernet'"

It seems as if the AP know two higher power levels (up to 20 watts?) whilst the switch only goes to 15.4 watts. Sometimes clients then get disassocieted from this AP. How could I fix this? Is it a firmware upgarde on the switch? Does the PoE switch HW need to be replaced? Or is it harmless and the disassociateions have probably an other reason?

--Joerg

22 Replies 22

jeff.kish
Level 7
Level 7

The Cisco 1250, as with all 802.11n access points, requires somewhere in the vicinity of 18W in order to operate. Standard 802.3af PoE only supplies up to 15.4W, so your switch is not able to supply full power to the AP. That gives you two options:

Your first option is to disable one of the radios on your 1250 (either 2.4GHz or 5GHz), and it will operate fine with standard power.

Your second option is to supply full power to this AP. You can do this with a Cisco power injector for the 1250, or you can simply plug it into the wall where it's mounted, if possible. Finally, you can do this through Cisco Enhanced PoE, which requires an E-series switch and a software upgrade.

Once the IEEE releases the 802.3at PoE+ standard, Cisco will make switches that can supply enough power by default. Until then, we're stuck with these limited options.

Jeff is right, but the E-Series switches can give you 20w of power to the ports which will allow you to run the 1252 in full 'N' mode.

-Scott
*** Please rate helpful posts ***

If you have an e-series poe switch, then the command to enable the port to allow up to 20watts is the following

int gi1/0/blah

power inline port maximum 20000

Also make sure it's running the latest IOS code.

Liamo

Aaron
Cisco Employee
Cisco Employee

This is a pretty complicated topic. Here's the executive summary on

the current status:

The 1250 can now run both radios in 802.11n (albeit at reduced

tx power and with only 1 tx antenna) from 15.4W, and with 2 tx antennas

(reduced tx power) from 16.8W which the 6500 can now supply with some

line cards.

See the 12.4(10b)JA3 / WLC 4.2.112.0 release notes for more

details.

For the 6500, need WS-F6K-48-AF and 12.2SXH2 per

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/voip.html

So ... if you are running at least 10bJA3/ 4.2.112.0, then getting

15.4W 802.3af should not be an operational problem.

If you are running the right WLC code version and have set up the right

powering scheme to power your APs as desired, yet are still getting

bombarded with unnecessary WCS alerts, then it's problem time to open

a TAC case and get these cleaned up.

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I have WLC code 4.2.176.0 and have switch 3750E version 12.2(35)se5. I have access points 1252's but it seems that my switch is not providing enough power, the max is 15.4 watts. But I thought that this specific switch is capable of doing the max of 20. Do I need an upgrade or a specific command? Any help is appreciated. Thanks.

1. Your 3750E is running the wrong IOS. I believe it should be running the 12.4(44) IOS.

2. Next you have to configure extra power to the port using the command power inline port maximum 20000 .

If you don't want to upgrade the IOS of the switch, then upgrade the firmware of the WLC to version 6.X and this will allow the 1250 to operate both radios BUT AT A COST of lower MCS rates.

Hope this helps.

Please rate when this post is helpful or answers your query.

Thanks for your response, I hope you meant 12.2(44) because I couldn't find any 12.4(44) releases. I will upgrade my switches and hopefully this resolves the issue.

My apologies. It's 12.2(44).

dimensyssrl
Level 1
Level 1

Hello.

We have a 4507R-E switch with same problem.

But from configuration I can only set 15,4 W maximum...

Is it 4500 limit?

Thanks

Daniele

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