Citation :
The Wifi
1. What is it?
Wifi means Wireless Fidelity. It?s a network protocol. Indeed, Wifi be able to communicate with others computers or devices networks but wireless. For example, he can be used in the street, in a public building, in your car, trains and in future why not planes. The wifi technology uses the radio waves at a specific frequency.
In Wifi, we have ten standards: 802.11a, b, c, d, e, f, g, h, i and j. However, only 3 standards are used: a, b and g.
- 802.11a : it?s the less give off, he use the 5ghz frequency for communicate.
- 802.11b : it?s the more give off, he use the 2.4ghz frequency for communicate.
- 802.11g : it?s the future standard, he has the best rate.
2. How does that work?
In Wifi, there are 2 modes: ad hoc and infrastructure.
First mode, infrastructure. In this mode, computers and network devices communicate with only one network wifi device called access point. Access point manages traffic.
Second mode, ad-hoc. In this mode, computers and network communicate with all. There don?t have a device who manages traffic.
The Infrastructure mode is better but more expensive. Indeed, traffic is managed by one device so we can see who is on the network, we have a better rate than ad-hoc mode but we must buy an access point so that more expensive.
I will describe wifi devices and wifi software.
So, this is 2 wifi router. A wifi router is composed to a router and a access point. Router can be able to connect and share a network connection for example internet and access point can be able to access to the router from a wifi computer. This is a wifi card, she can be able to access to the router from a computer. This card is connected in a computer. However, there are others interfaces cards for example usb, pcmcia. 3. Range, Rate and Security
In this part, I will talk about only 802.11b and g because 802.11a is the less give off.
- Range : In Wifi, the rate depends to distance and environment. We can see on the picture that the theoretical rate in function of distance. In black, it is the rate out of building, in green it?s the rate in a building without wall and in blue it?s the rate in building with wall. We can see that in theoretical the range is about 400 meters out of building and about 100 meters in building. However, this is a theoretical range, in practical the rangeis divided by 2 so 50m in building and 200m outside.
- Rate
For the 802.11b, the theoretical rate is 11megabits by second and for the 802.11g the theoretical rate is 54 megabits by second. However this rate depends to distance and environment and it is a theoretical rate.
Always on this picture we see that the rate compared with distance and environment. The rate isn?t very stable. Indeed, wifi use high frequencies and this are very sensitive to noise. So more is the distance is long more the signal is bad. We can see that the maximal rate is possible on a small distance. It?s a big inconvenient!
For 802.11g the maximal rating is shorter.
Moreover, on this picture this is a theoretical rate. In practice, the rate is about 60 percent of the theoretical.
- Security
A lot of firm would like install wifi network however for a firm security is very important. Indeed, wifi use frequencies and this propagates every where. So we will see the different ways to secure a wifi connection:
First, wep key. Wep key is a combination of characters. If this one is activate, to connect you to a wifi network you must enter the key. For a maximal security the key is long of 64, 128 or 256bits.
Second, filtering mac. Each network card has a address mac. This address is single in the world. So on the access point we can authorize or not an address mac to connect to the wifi network. This way is very efficient.
Third, we have the VPN. VPN means virtual network protocol. This one is very use to create a network connection on the web between to firm for example. To secure a wifi network we can use this way. This way is use by firms because is the hardest to hack.
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