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Don't listen to rumors
The internet is full of advice: both good and confusing. It is not easy to choose the right one, often the information printed on the boxes or in the instruction manual of a typical Wi-Fi kit will not help much. Rather, there is a guide to installation, often by using a wizard made very easy even for a complete novice user, but usually not a word about dealing with problems that the embedded software should solve.
"If you find that your neighbor is using the same Wi-Fi channel, try switching your router to one of the neighboring channels" or "There are 13 usable Wi-Fi channels, so even in an overcrowded area you should find a free one." As you'll see in a moment, both of these statements reveal that their authors know little about how 802.11 works.
The birth of the standard
Let's start with a quick technical overview of Wi-Fi. What does this system look like today and where did it come from? We will go back to the early nineties for a moment, when there were several different radio communication devices on the market, but no standard was in force.
In those days, the market was dominated by Xircom, Netwave, Proxim, and even IBM, but none of their products could get along with a device made by another company. This was to be remedied by the ratification of the 802.11 standard, which took place in 1997.
The original 802.11 band recommends using the 2.4 GHz band for communication, which is one of the bands originally reserved by international agreements for industrial, scientific or medical purposes. Interestingly, at the time of definition, this band was excluded from being used for communication purposes.
The ban did not last long. In later years, it was allowed to use it for other purposes, not only for communication. As a result, there is, for example, the frequency of the magnetron in its center, with which you heat the soup in your microwave oven. And many others.
In pioneering times, it didn't bother me. The specification of the 802.11 standard referred to transmission rates of one or two megabits per second. In the days of dial-up Internet access of 56 kilobits per second, this was enough for most applications.Where is the noise coming from?
Adjacent wireless networks aren't the only obstacle to your Wi-Fi. There has already been talk about microwave interference. Wi-Fi operates at such low signal levels that even the best-shielded stove can interfere with a nearby system. Keyboards, mice, screens, radio headphones and many other gadgets also want to share the common band.
Poorly constructed, cheap devices can also be a source of interference. Not only can they emit in the fundamental frequency, but also in harmonics. Some can transmit peak-like signals that interfere with more channels.
In such cases, programs like inSSIDer will not help. They are designed to scan signals compliant with the Wi-Fi convention and capabilities of the card in your laptop. They do not see this non-standard radiation, even if they feel its negative presence.
Too tight channels
As can be seen in the attached table, in addition to the 2.4 GHz band, the standard variants include 802.11 a and 802.11 n, transmitting in the 5 GHz band. However, this is a song of the future, today almost every network uses 2.4 GHz and this band is the most problematic.
*) The system has received many improvements (G +, SuperG, etc.) introduced by chipset manufacturers. They have never been officially ratified and may not communicate with each other in the highest modes.
In the 802.11 standard, the 2.4 GHz band is divided into several channels. Thirteen main ones start at 2.412 GHz for the first and increase by 5 MHz for each channel. Channel 14 is unusual, located 12 MHz above its predecessor. But you don't need to remember it if you don't live in Japan, the only country where it can be used. In turn, channels 12 and 13 are illegal in the United States. Due to these differences in installation time, a question is always asked about the location of the device.
In more crowded areas with wireless installations, tricksters, by deceiving the installer, open access to channel 14. This is illegal and we absolutely do not recommend it.
Most Wi-Fi users probably don't understand that not all of these 13 legally available channels can be used on their own. The channel is five megahertz and the transmission requires twenty, and in some "Enki" installations even 40. For this reason, it has to occupy several adjacent channels. In fact, the specification mentions keeping the width of 25 MHz with a small margin to avoid interference, but 22 MHz is practically sufficient. A spacing of just one channel would cause multiple transmissions to overlap.
Due to the overlapping of the channels, we only have room for three, not thirteen. In the United States, manufacturers recommend 1, 6 and 11, and besides, the country of 11 is sometimes replaced by 12 or 13. With this convention, choosing, for example, channel 3, others enter both basic, 1 and 6.
Other channels can sometimes be used as some degree of overlap with remote wireless networks is acceptable, but for maximum range and transfer you are limited to these three channels.
The most important diagnosisLinuxers and even iPhone users have tools to monitor Wi-Fi usage. Windows users have to get them themselves.
There are many of them, this time we will demonstrate inSSIDer, downloadable from MetaGeek. Graphically displays all the grids visible in your area, along with their relative signal amplitude.
The five-minute recording of signal strength is especially useful for businesses. This is the typical life cycle of a network. It will also be able to detect the passage of a mobile laptop between intelligent access points.
inSSIDer is exceptionally well suited for diagnosing environments where Wi-Fi users have complained of poor speed and frequent interruptions. Typically, their routers were found to compete for a time frame on the same frequency with devices from several neighbors. A quick switch to a less crowded channel is all it takes for the wireless network to go back to work.