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Wireless Client CCX Support Questions

I'm looking at high density wireless deployments at the moment.

Although there are a great deal of things you can do on the wireless infrastructure to reduce cell sizes through tx power levels and supported data rates, there seems little point in creating lots of smaller more efficient wifi cells if your wireless clients are still running at relatively high power levels, causing co-channel interference across a number of cells.

I have been looking for more information about the role of the 'AP-specified maximum transmit power' feature of Cisco CCX client extensions. I am guessing that this feature will match client power levels on clients with AP power levels in some way? (Is this DTPC?)

I've had a hunt around the CCX pages on Cisco.com and there seems to be very little information about how this mechanism actually works.

Is this something that is widely supported? I see it has been part of CCX since version 2. If a client supports CCX v2 or higher, is this feature supported as a mandatory item, or is it supported to varying degrees between manufacturers?

If anyone has any information about this feature, or could point me towards some useful information about this feature, I would be very grateful.

I recently reviewed the Cisco white paper about high density client environments in higher education, but it didn't seem to touch on this area, which makes me wonder whether I have mis-understood this feature? It would seem to be a killer feature to mitgate client originated CCI in high density environments.

Thanks.

Nigel

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New Member

Wireless Client CCX Support Questions

Nigel,

You are correct that this feature is also know as DTPC.  When enabled, the beacons and probe responses contain an IE 'cell power' with the DBm limit set to the AP's current Tx level.  In theory, this will limit the Tx of any CCXv2 or higher clients to that of the associated AP.  That being said, I have not fully tested this funtionality out to know how well it truly works.  Obviously, one huge hole is that a lot of personal devices, most smartphones and tablets being one of the biggest examples, do not play in the CCX sandbox. 

So while this feature can help slightly in a high density environment when devices support it, one of its main advantages is to prolong battery life for mobile devices such as phones that can safely turn down their Tx.

Sorry I can't give any real-world examples of this feature being a silver bullet for high-density.  Maybe others in the community have some more insight in that regards.

New Member

Wireless Client CCX Support Questions

Thanks Matt, this is good information.

I've done a little hunting around and it seems that few tablets & smartphones support CCX from what I can find. I guess that although they do not support CCX (and hence DTPC), they are generally lower power devices (as they have to conserve battery power). In a high density environment they should hopefully cause less client-originated CCI than laptops due to their lower tx power. For example, I did some digging around and it seems that the iPad transmits at about 10mW, so I guess that it lends itself quite nicely to smaller-cell, higher density deployments where AP tx powers are wound down to a lower level.

I'm guessing that with some clients that support CCX (i.e. laptops with appropriate wireless cards) using DTPC and smartphone/tablets running at lower power levels, maybe the client CCI in high density deployments mightbe more manageable than I first thought.

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