Overlapping v's Non-overlapping channels...

[darrenj]

I know it is bad practise to have more than one AP within the same cell area using the same channel, but wondered what the effects of this were. For example, if I had an AP in channel 6 and another AP ten yards from it in channel 6 also, what would be the repercussions?

Thinking about it logically, there would be radio collisions. Each AP could potentially try to transmit at the same time causing collisions. Therefore, you would see slow throughput and high error counts on the AP? Also, if a WLAN client transmitted a frame to a user on the wired network, each AP would receive it (regardless of association) and forward the frame on - resulting in the wired client receiving two copies of the same frame (one from each AP)???

Can anyone, explain why it is not good practise to have over-lapping channels (or any useful web links/documents)?

I will continue to use non-overlapping channels, but it would be nice to know why.

Thanks

[Rob Huffman]

Hi Darren,

That is a great question. Here are some links that have really good answers;

Channel Deployment Issues for 2.4-GHz 802.11 WLANs

From this doc;

http://www.cisco.com/en/US/products/hw/wireless/ps430/prod_technical_reference09186a00802846a2.html#wp134263

Assigning 802.11b Access Point Channels

An important concept to note regarding channel assignments is that the channel actually represents the center frequency that the transceiver within the radio and access point uses (e.g., 2.412 GHz for channel 1 and 2.417 GHz for channel 2). There is only 5 MHz separation between the center frequencies, and an 802.11b signal occupies approximately 30 MHz of the frequency spectrum. The signal falls within about 15 MHz of each side of the center frequency. As a result, an 802.11b signal overlaps with several adjacent channel frequencies. This leaves you with only three channels (channels 1, 6, and 11 for the U.S.) that you can use without causing interference between access points.

From this link;

http://www.wi-fiplanet.com/tutorials/article.php/972261

Channels and international compatibility

Although the statement that channels 1, 6, and 11 are "non-overlapping" is incomplete, the 1, 6, 11 guideline has merit. If transmitters are closer together than channels 1, 6, and 11 (e.g. 1, 4, 7, and 10), overlap between the channels will probably cause unacceptable degradation of signal quality and throughput.

http://en.wikipedia.org/wiki/IEEE_802.11

Hope this helps!

Rob

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