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5 GHz, the problem of Russia and Europe
Big problems developing the 802.11n standard associated with the frequency range of 5 GHz. Recall that the standard B and G use the frequency band 2.4 GHz --- license-free band, which uses and other peripherals: cordless phones, radio modules, etc. In this band 13 channels are available, but in densely populated areas are often situations when they are overloaded, the connection is problematic, there is a conflict. Not to mention that the banal microwave degrades signal quality. Among the possible solutions have been chosen to use the frequency band 5 GHz. In the United States it is an open frequency range, which already runs the standard 802.11a.
In Europe and Russia, the situation is more complicated, since this frequency range is reserved for military purposes. These frequencies, among other things, are used by radars, and this is a real problem. As a result, 802.11a products are banned in Russia for use. In Europe it is requested to release this frequency, but the problem did not end there.
Radars are still using this frequency range, so the producers had to integrate the modules for the 5-GHz band protocol DFS (Dynamic Frequency Selection). Its principle is simple: before using the band 5 GHz main device (wireless router) to check the presence of radar signals. If the signals are detected, you will have to move to a new frequency. If the signals are not found, will use this frequency, but the router will continuously monitor it. If the interference will be detected, then the transfer will be stopped, the router will have to find a new channel. By European standards, you can use equipment that meets standards DFS 1.2.3, while in March 2008 planned output standard 1.3.1, which will include the results of recent studies. Yes, you guessed it, all products comply with Draft 2.0 Standard 1.2.3.
In some European countries, in particular, in France, in December 2005 issued a decree ordering that all the 5-GHz peripherals standard 1.3.1. Therefore, standard equipment 1.2.3 officially sold there is not. Everything becomes more complicated, given that the transition to standard 1.3.1 requires making physical changes to the modules to match the new protocol monitoring. What do sellers with the periphery draft 2.0? It is necessary to disable the use of 5 GHz, which significantly reduces the advantage of new modules. Another option - reducing the number of channels available in the 5 GHz band, from 11 to 3. But then in densely populated areas increases the chances of conflict.