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• Oliverda Topikgazda

  #66 2009-11-25 17:09:01

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  Oliverda

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  There are only 3 non-overlapping channels available in the 802.11b standard.These are Channels 1,6, and 11. For WiFi access points that are located near each other it is recommended that they each use one of the above non-overlapping channels to minimize the effects of interference.

  This overlapping of 2.4GHz channels are better visualized from the chart below.

  

  Two WiFi networks operating on the same channel are forced to share bandwidth, as they can't "talk" simultaneously, which halves each network's bandwidth. In order to evade this effect, you need to change your access point's channel, but taking the adjacent one won't do it, as WiFi channels are arranged in an overlapping pattern, as you can see from this scheme:

  Channel 1 overlaps channels 2 to 5, which therefore may not be used for a neighbouring WiFi network. If channel 1 is used, you should switch to channel >=6.

  There must be a spacing of at least 5 channels (or more) between each WiFi network in order to avoid interferences.

  Spectrum assignments and operational limitations are not consistent worldwide. Most of Europe allows for an additional 2 channels beyond those permitted in the U.S. for the 2.4 GHz band. (1–13 vs. 1–11); Japan has one more on top of that (1–14). Europe, as of 2007, was essentially homogeneous in this respect. A very confusing aspect is the fact that a Wi-Fi signal actually occupies five channels in the 2.4 GHz band resulting in only three non-overlapped channels in the U.S.: 1, 6, 11, and three or four in Europe: 1, 5, 9, 13 can be used if all the equipment on a specific area can be guaranteed not to use 802.11b at all, even as fallback or beacon. Equivalent isotropically radiated power (EIRP) in the EU is limited to 20 dBm (100 mW).

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