AP1252-AG with Cat 3560 / Cat 3750

Unanswered Question
May 22nd, 2008

Hi All,

please advise, I am probably not the only one, but I have come to realise that 15.4W provided by switch ports on 3560/3570 catalysts is not sufficient to power up an AP1252-AG dual radio device. I have read the spec and it says that a dual radio AP requires 16.9W, but a single radio AP will consume/need 12.95W plus a little more depending on the ethernet cable length. As a test I physically removed one radio from the AP1252-AG and tried to power it up via poe port on switch. The AP powered up OK with just one radio module installed.

However the AP cannot be installed with one module removed, so my alternatives are to either power the AP with direct power supply or use the Power Injector which will provide enough power to start both radios.

I was wondering whether it is possible to have both radios installed 2.4/5.0 Ghz but have one disabled through the software, so that the AP will only effectively be running with one Radio Module (UP), but it will have two Radios installed physically.

I have tried this numerous times, when I try to use poe for the ap, it negotiates with the switch port that it need more power for the two radios, the switch can't provide it so it goes into low power mode.

I was hoping that by disabling one radio and then booting the AP it would only request enough power to feed 1 radio, the switch would be able to provide the requested amount and then the AP would work. But I cannot get this to work, Is it at all possible?

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Overall Rating: 5 (6 ratings)
jeromehenry_2 Thu, 05/22/2008 - 05:32


That is not possible. You AP with both radios, even one being off, will still eat more power than one single module... I tried, having the same hope...

Your only possibilities are:

- power brick

- 3560/3750 E series

- 1 single module...

hope it helps


ahkal_cisco Thu, 05/22/2008 - 06:06

Hi Jerome,

Thanks for replying

Can't upgrade to "E" type Cats - too expensive, no point taking the radio out - if I do it is a waste of investment in dual radio AP, so it looks like I will have to buy the Power Injector module.


Reitenbach Wed, 05/28/2008 - 07:22

Same Problem here!

Another question: what are restricitons if i use

only 1 Module. Do i have 2 choose between a/n or

g/n or a/g combination in this case? Dont really understand, what is the benefit 2 make 1252 modular.

jeromehenry_2 Wed, 05/28/2008 - 07:31

You have to choose between 5Ghz radio (a/n) and 2.4 Ghz radio (b/g/n)... the benefit of having a modular 1252 is (probably among others) that if the final 802.11n protocol is very different from draft 2.0, on which the 1252 is based, you'll be able to exchange the radio module you plan to use 802.11n on...

and hey, with one module only you can use your AP with a classical PoE...

Scott Fella Wed, 05/28/2008 - 07:32

You can purchase the 1252 with no radios, one radio or both. That makes it modular... some don't require the 5GHz radio and might just purchase the 2.4GHz.

If you want to run 802.11n, then you will have to run that on the 5GHz radio unless you only have one AP in which you can run it on either the 2.4GHz or the 5GHz. The reason being, is channel reuse. When you bond two channels on the 2.4Ghz, you have to use 2 out of the three which limits you only having one channel for a neighbot ap on the 2.4GHz. 5GHz has more channels you can use and that is why 802.11n will be most likely deployed on the 5GHz side.

Reitenbach Wed, 05/28/2008 - 07:38

Thx and sorry for dumb questions. Im new in Cisco Whireless World.

Another Question to the Topic: If i understand it right, Power Injector is the cheapest choise in combination with a 2960 PoE switch for using 1252AG with two radios?

Do i need a PoE Switch in this Case?

jeromehenry_2 Wed, 05/28/2008 - 07:47

Hi Reitenbach,

If you use a power brick, you don't need anything else, your 2960 can be PoE or not on that port, it doesn't matter, and yes you can then use both radios.



Reitenbach Wed, 05/28/2008 - 09:45

My goal is 2 create a closed whireless network.

If i use Power injector 4 each AP, so i dont need a switch in this installation?

jeromehenry_2 Wed, 05/28/2008 - 09:50

Well, APs provide access to wireless clients to... what, in your case? You probbaly want to connect your APs to a switch so that wireless clients to one AP can send information to wireless clients on another AP... or do you have a different setting in mind?

Reitenbach Wed, 05/28/2008 - 10:00

2 another clients in a network established by 6-12 AP's and controlled by a wlc

jeromehenry_2 Wed, 05/28/2008 - 10:03

Then you definitely need a switch (unless you have different sites and routers) to connect your APs and your controller, so that all can communicate with each other. If you have a power supply, the switch does not need to be PoE.


jeromehenry_2 Wed, 05/28/2008 - 10:17

Well yes, if the clients are in range of the same AP, they will use the AP to communicate with one another. But if you have several APs, say one AP in one room and another AP in another room, then usually signal travels from wireless client 1 to AP 1 via the radio, then AP 1 forwards the packet over a cable to a switch that relays to the second AP, then the second AP relays the signal wirelessly to the second client. This system is used because usually APs would not use their radio to talk to each other, for many reasons.

In your case, if you have a controller, Aps need to talk to the controller, and the controller doesn't have any radio anyway, so you need cables to connect to your controller. If it is a 2100 controller, you can forget the switch and connect your APs to the controller.

If you have a 4400 series, you need a switch as APs cannot connect directly to 4400 controllers.



Reitenbach Wed, 05/28/2008 - 10:35

Yep thats it i have 2106 Controller (i will have)and it has 8 Ethernetports. Thats why im asking.

jeromehenry_2 Wed, 05/28/2008 - 10:40

Okay, so you don't need any switch as long as your APs are less than 100 m away from your controller. Just plug the APs to your controller, and power each of them with a power brick...


Scott Fella Wed, 05/28/2008 - 07:48

You need the E-Series switches that can supply 20W that is required to power up the ap's. If you don't have too many ap's and don't care about looks, then the power injector is your best bet. Using other PoE 802.af switches that don't supply 20W, then depending, you will run them in reduced power and might only be able to power up one radio only.


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