  WIFI Generalities
[20 mn of reading - published 5/10/2004 6:46:03 PM - Target : Débutant]
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Author
1. Presentation
With a connection Wifi it is possible due to points of distributed accesses to various places of a building to connect by way of a network Wifi card in a network without wire allowing access to the high output. It's possible to move with the laptop, PDA in a more or less important perimeter according to the characteristics of the material and the environment.
The objectives of Wifi are to replace on one hand the wire network. This technology would allow the users to disregard constraints brought with cables RJ45. More need to look for a grip of connection during a movement, less time for the implementation of a network, less works so capital costs and weaker financing. And on the other hand, the fact that Wifi uses waves radios it is interesting to be able to create points of available accesses for the travelers for example which looks for an access to Internet. It would allow to create a new community based on sharing information ( www.paris-sansfil.fr ). The use of Wifi in the rural zones as for them, exclude from the high output by way of standard telephone lines output set up with rather powerful broadcasting stations could benefit from a high access to supply a qualitative signal on long distances.
At present, Wifi is rapidly growing, one esteems that, by 2005 , 90 % of the portable will be equipped with an adapter Wi-Fi.by Centrino technology of Microsoft, and the number of " Hot-Spots " does not stop increasing. This " Hot-Spots " allows an access to Internet and to specific services following their places. The phone operators are the most present on this domain such as Orange, which covers already more than 1500 " Hot-Spots " Wifi in France and wishes to reach 4000 " Hot-Spots " by the end of 2004 by increasing these points in the big sites (airports, stations, …).
802.11a |
54Mbits/s (30Mbits in fact). The reach is limited in 30m. She uses the wave band of 5GHz on 8 canals. |
802.11b |
It is standard the most known and the most used at present. She offers a theoretical output of 11Mbits/s (6Mbits in fact). The reach can achieve 300m outside. She uses the wave band of 2,4GHz on 3 canals. |
802.11c |
Complement to the MAC layer allowing to establish a bridge with wefts 802.11d. |
802.11d |
Supplement of the standard 802.11. She allows an adaptation of the physical layers of devices to be in keeping in the requirements of certain countries. |
802.11e |
She brings a quality service to networks 802.11a, b and g at the level of the coat layer connection of data. She allows a better transmission of the voice( ex : voice IP) and of the video. |
802.11f |
Defines the protocols of communication between the points of access. She allows better one interoperability between the points of access with the material during a movement, it is the roaming. |
802.11g |
54Mbits/s (30Mbits in fact) on the wave band of the 2.4 GHz. Standard 802.11g allows an interoperability with the standard 802.11b, the materials corresponding to the standard 802.11g can work with the busy band of the 802.11b. The reach is similar to the standard 802.11b. |
802.11h |
Improvement of the coat MAC layer aiming to move closer to the standard 802.11 of the European standard (HiperLAN 2). She allows the automatic control of the powers of broadcasts as well as the automatic assignement of the frequencies of access point. Adoption of TPC technologies ( Transmit Power Control) and DFS ( DYNAMIC FREQUENCY SOLUTION) for a correspondence with European standards. |
802.11i |
Improvement of security transmission of standards 802.11a, b and g to remedy the weaknesses of keys WEP with a new algorithm of encoding: the AES ( ADVANCED ENCRYPTION STANDARD). |
802.11IR |
Standards consisting in using infrared signals to communicate. Technically exceeded but always present. |
802.11j |
Japanese naming of the European standard 802 .11h on the frequencies of 5GHz. |
802.11k |
Elle permet l'utilisation de la géo localisation par des services de recherche. |
802.11n |
Future standard after standards 802.11b and g authorizing theoretical outputs of 100Mbits /s. In the course of development, exit foreseen for 2005. Info here. |
1.4
Rule
The rule of waves radios is very strict. The fact that wavebands are not stretchable, it is necessary to apply standards to avoid quite risks of interferences.
Since the liberation of the frequencies of 2,4GHz by the army. The increase of communications using this wave band does not stop growing. An European standard was established to allow the use of Wifi on 13 canals not to disrupt the communications of the army, neighbour of this frequency of 2,4GHz; because the increase of the number of canals decreases the possibility of interferences with the other nearby frequencies.
The powers of broadcasts, the PIRE is limited by the ART (Authority of Regularization of Telecommunications). The offenders incur six months of prison and 30 000 € of fine with seizure of the material, according to the article L39-1 of the code of the PTT …
Tableau établit par l'ART concernant les puissances autorisées :
Frequencies |
2400MHz |
2454MHz |
2483,5MHz |
Inside |
100mW |
Outside |
100mW |
10mW |
Main borders available Wifi on the market do not allow regulation of the PIRE. According to the used canals, for an outside use a regulation is necessary to limit the PIRE in 10mW because for the best broadcasting stations power can achieve 85mW ( Linksys WAG54G).
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Brice PIROLLET
[15 mn of reading - published 5/10/2004 6:45:40 PM - Target : Débutant]
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