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Cisco 1252s with regular 802.3af PoE switches - what are the impacts?

Does anyone have any real-life experience with deploying the 1252s on regular 802.3af PoE switches?  I have a few 1252s one some 3560 PoE ports and the show up with "low power" alarms.

I am wondering what the real world impact is with this scenario.  The 1252s have both 2.4 Ghz and 5.0 Ghz radios in them and I have HT enabled on the controller.

I'm wondering what capabilities I am losing by running on 802.3af power besides the annoyance of the alarms.

Thanks in advance!

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: Cisco 1252s with regular 802.3af PoE switches - what are the

Hi,

This is the comman issue... the 1252 AP needs Enhanced POE Ex- 3750-E switches to get all the radios up and running.. if we are using just a 802.3AF then only one frequency can be enabed and the We cannot get N speeds.... the below link will explain you better..

http://www.cisco.com/en/US/prod/collateral/wireless/ps5678/ps6973/ps8382/product_data_sheet0900aecd806b7c5c.html

Let me know how this works out for you!!

Regards

Surendra

5 REPLIES
Cisco Employee

Re: Cisco 1252s with regular 802.3af PoE switches - what are the

Hi,

This is the comman issue... the 1252 AP needs Enhanced POE Ex- 3750-E switches to get all the radios up and running.. if we are using just a 802.3AF then only one frequency can be enabed and the We cannot get N speeds.... the below link will explain you better..

http://www.cisco.com/en/US/prod/collateral/wireless/ps5678/ps6973/ps8382/product_data_sheet0900aecd806b7c5c.html

Let me know how this works out for you!!

Regards

Surendra

New Member

Re: Cisco 1252s with regular 802.3af PoE switches - what are the

Surenda,

Thanks for the information.

Do you know if there is a smaller Cisco 802.3at switch available? In most of our buildings we have at least one wiring closet on each floor which means that we rarely have more than 8 access points home-running to each closet. I would rather not purchase a 24 port 802.3at switch if we're only going to use less than six ports.

I'm not a fan of power injectors. It definately limits my ability to restart an AP from my desk, and where I work we have almost 2000 radios.

Thanks again for your help.

Tim

Re: Cisco 1252s with regular 802.3af PoE switches - what are the

Hi,

I had a very similar problem and the "enhanced power" switches gets VERY expensive real quick. I also didnt like the PoE injectors, just for the reason you mentioned. PowerDsine makes power switches, "managed" power switches. They come as small as 6 ports and as high as 48 and provide 802.3at power to edge devices.

http://www.microsemi.com/PowerDsine/Products/Midspan/PD_9000G.asp

I hope this helps ...

Good luck to you

__________________________________________________________________________________________ "Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin ___________________________________________________________
Hall of Fame Super Gold

Re: Cisco 1252s with regular 802.3af PoE switches - what are the

Someone from Cisco TAC (I don't remember who) posted here confirming that you can use 15.4w to power up BOTH 1250 radio modules IF you run IOS version 12.4(10b)JDA3 and later (and for controller-based it's 5.2.X and later).

HOWEVER, with this scenario, it comes with a COST of the upper two MCS rates are disabled and the transmission power is slightly lower..

I've been running some of my 1250 with 15.4w since June 2009 (much to the chagrin of some of the TAC).

New Member

Re: Cisco 1252s with regular 802.3af PoE switches - what are the

Sorry in advance for the book I have just written.

I have three 1252s on 75 feet of Cat5e cable running to a 3560 PoE switch. Sometimes, but not always, I see a low power alarm on the access point(s). This is in a small building that is built like a fortress so the RF environment is somewhat challenging. I am watching WCS closely and see all three 2.4 GHz radios powered all the way up to power level 1. I notice that two of the 5GHz radios are on power level 1, and one is on level 3. I thought that RRM would not power anything down until you had at least four access points as RF neighbors. I believe I read that in a Ciscopress book and it seems to be true everywhere in our network when I look at buildings with 3 or less WAPs.

The building in question does not have any other buildings close by with any 5GHz radios in operation - or at least I didn't see any when I did the survey.

I'm wondering if the power setting of the radios is also related to the length of the Cat5e cabling. Seems to me a shorter run would have less resistance than longer runs, allowing the radio to have more power.

My main concern is not this building in question, since we went for coverage and not client density in the design. We several other buildings on the radar, all libraries, which are going to be both RF challenging (bookshelves, furniture, cubicles, cubbies) and client-density challenged. These buildings have hundreds of WLAN clients in them at times - and I mean devices, not just people.

Someone else told me (reputable source) that channel bonding is not an option when on 802.3af power. Makes sense, actually. I would never even think of bonding in the 2.4 GHz range for obvious reasons, but up in the 5GHz range it is a definate possibility in these buildings. Seems to be that we might be shooting ourselves in the foot by not using 802.3at power in these buildings.

If channel bonding is disabled and the upper two MCS rates (using 800ns guard interval) of 117 and 130 are disabled, then I'm looking at maximum MCS rate of 104 Mbit/s compared to 270 Mbit/s with 802.3at with channels bonded in the 5GHz range.

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