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39

# WiFi collisions

Posted on: Oct, 15th 2010
If your WiFi disconnects constantly or is slow, despite of have the access point or the router near, and you don't know why, in this post, with a probability of the 99% you will find the solution to your problem.

You can't see the WiFi networks although are occupying the radioelectric space of the neighbors and ours, colliding one networks with others impeding in a lot of cases the communication. As more WiFi networks there are in our environment it will be more probable that our network collide with some of our neighbors.

The WiFi transmission is realized through the electromagnetic waves that work in channels near to the 2.4Ghz of frequency. There are thirteen different channels that can use a WiFi network (eleven if we are in the U.S.). These are separated by intervals of 5 Mhz. The bandwidth required for the transmission, using the standards 802.11b/g/n, is of 22 Mhz, therefore the ranges of frequency of these channels aren't totally independent, but are overlapped ones with others colliding between them, so really, as maximum, we can have three channels totally independent. The optimal combination is the 1, the 6 and the 11 if we are in the U.S, if not is the 1, the 7 and the 13.

U.S have two channels less due to the legal restrictions that rules the use of the radioelectric space in this country.

Imagine the quantity of collisions that must be in a flat when almost all the neighbors have hired the same provider of internet that have installed the same router that comes configured by default always in the same channel.

Knowing that we can try to solve the problem investigating the channels that have configure our neighbors, in order to change the one we are using us in the configuration of our router. To see the channels of our neighbors, in GNU/Linux or Mac OS we can use a tool called Kismet, that have a lot of functionalities to check the network security, because it can be used as sniffer, get the MAC of the computers conected to the WiFi networks, etc. If you use Windows you can use the Network Stumbler, a lot of more easy of use but more limited in functionalities. Really, is a utility to do Wardriving (drive in car looking for open WiFi networks). The two tools are free.

When we have get the list of the channels that use the neighbors we can choose the one that is more away of the others and if not is possible, the one that is less saturated, trying of having into account also the power of the signal that arrive from the occupied channels.

However is more secure and almost never fails is connect by cable always that it be possible.

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En español: Colisiones WiFi