Overlaping

Unanswered Question
Feb 7th, 2007

Hi,

we have a WLAN implementation of several AP's in a shopfloor area, and we were having some troubles. Has I red about overlapping rules, I went to the problematic areas and I could see in one location over 5 even 6 ap's. I asked the vendor that implemented and he answered:

There are only three "non overlapping" channels, that means that channel 1 (2.412gHz), channel 6 (2.437gHz) and channel 11 (2.462gHz) are separate from each other with 25mHz; so they don't begin in the bandwidth of each other.

But if you take channel 2, who is 2.417 gHz and channel 7, who is 2.442 gHz you will also have 25 mHz bandwidth!

You have to try that the neighbours have a channel difference of +5, in between the 13 channels for Europe.

It is true that it is better to have the maximum of the bandwidth, and specially if you do voice over IP, but for terminal emulation it is not problem to work with a difference of +1, because they send only small packets.

So if you see 6 access points from one point in the manufacture, it not a problem, but they have to have different channel numbers!

Is this true?

I have this problem too.
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Different cards have varying degrees of sensitivity. You could set your APs to any channel you would like given that the appropriate precautions are taken, however this is not advised.

Please take a look at this link:

http://www.cisco.com/en/US/products/hw/wireless/ps469/products_data_sheet09186a008008883b.html

The link is to the Cisco antenna reference guide, however if you scroll down you will see a graphic which describes the overlapping that may help you understand.

The issue with having overlapping channels isn't so much 'bandwidth' as it is interference... One could make an argument that due to the bandwidth you have the interference however lets leave that alone for the moment. You end up with whats called ACI or adjacent channel interference. Where two separate devices are attempting to communicate and are partially overlapping one another.. This can cause a wide range of issues from connectivity, speed, and a mixture of the two ;)

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