Wireless Access Point too close?

Posted on 2014-01-15
Medium Priority
Last Modified: 2014-01-21
Hi Experts,

This probably is an easy question.  I just want to know If you have 2 AP's close together about 12 feet's apart, which of the access points  will reduces the transmission power?

All access points are Cisco LAP and are control by a Cisco wireless controller.   The reason I am asking is because, in the office we have one AP that does not cover the entire room do to a very thick wall that separate the room(beam).  I am scare to put another AP on the other side of the room which is only 12 feet's away, because it might be too close, and the other AP might reduce the power transmission affecting the "good side ".

For the the record, the good side receives 5 signal bars and the bad side, which is about 12 feets only get 2 bars.

What do you experts adivce?

Question by:tech-gineer
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LVL 25

Accepted Solution

Ken Boone earned 500 total points
ID: 39784457
So you have a lot of options.  The main thing you don't want is to have the 2 APs on the same channel or overlapping channels.  They can be 2 feet apart as long as they are on different channels and it should not interfere.  So if you are on the 802.11b/g/n frequency then channels 1,6 and 11.  

Now if you have the controller set to auto select channels and auto select signal strength - which really that is what it is designed to do it should handle this for you.  But I have seen it reduce transmit power before where it wasn't warranted.  If it does just override it on that AP and manually code it.

You should be fine though.
LVL 47

Assisted Solution

by:Craig Beck
Craig Beck earned 500 total points
ID: 39787038
With a Cisco WLC you don't usually see the WLC reduce an AP's TX power until there are 4 or more APs seeing each-other.  4 is the magic number to get a reaction from an AP, as there will be no issue with 3 APs all sat on top of each-other as long as they're on channels 1, 6 and 11.

RRM will see that there are two APs on the same channel when 4 APs report to the WLC that they can see each-other.  The WLC will adjust the TX power on what's referred to as 'the third AP' (this is the third strongest AP as reported by the AP who triggered the RRM event) until its signal is less than -70dBm according to the reporting AP (providing that TPC is enabled).

A channel change will only usually occur by default if an AP is rebooted (the booted AP will be assigned the clearest channel), or if Event-Driven RRM is enabled (and DCA is also enabled on that particular band).  If your AP and WLC support it though you may have CleanAir enabled.  That would cause an AP to change its channel if the quality of the channel drops below a certain threshold (75% quality IIRC), but that's usually based on non-802.11 interference.

So, to answer your question, none of the APs will reduce their power if you only have two APs.

Author Comment

ID: 39787367
Great information from both of you, I have learned a lot!!  One last thing,  If the ethernet cable I am connecting from the "wall port" to the "AP" is 3 feet's and I change it to a 15 feet cable to be able to run the AP to the other side, will the speed of the AP be reduce because of the length?

In other words, is it better for the AP to be close to the wall port or that really does not matter?
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LVL 25

Expert Comment

by:Ken Boone
ID: 39787420
It won't make a difference.  The length of that cable has to fall within the specs of an ethernet cable which is 100 meters.  So in reality you won't see any difference whatsoever.

Author Comment

ID: 39790058
Will test and will confirm by Monday....  hopefully all should work well.


Author Comment

ID: 39797358
It seems to be working fine!!


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