Egy kis elmélet
WLAN - telepítések épületen belül
This is a continuation of the article titled "WLAN in single-family house'. Here we will discuss WLAN networks in other sites, such as offices, agencies, lecture halls, warehouses and the like.
When starting to design a wireless network, first of all we should decide, whether it will be a public one, such like in a library or an agency, or designated only for limited number of office, agency or warehouse employees. Next we should calculate how many users are to be logged simultaneously into the network - whether it will be a predefined number of office employees or hard to estimate number of public users.
If the network is to work in an office block, the biggest problem to solve is the existence of numerous walls and several floors, and therefore attenuation of signals by walls and ceilings. In the case the network is to be used in the whole building, there will be needed several access points. According to the rule of ''three walls and two ceilings'' we may anticipate that access points should be installed on every third floor and in every fifth office. Of course necessity of such installation should be checked in practice: perhaps more access points will be necessary to provide uninterrupted network access. First of all it depends on the walls' quality: whether they are light partition walls with very low attenuation or thick walls of an old tenement house, where radio signal attenuation is very high. The final effect depends on actual tests.
Wireless network in an office block, where several access points were applied, usually has greater capacity than needed for the limited number of employees. This is due to the simple fact, that each access point supports up to 20-30 users - if we multiple this value by the number of actually installed access points, we will receive theoretical capacity of created wireless network. But it should be taken into regard that when such network is designated to be public, the most loaded access point will be the one in main hall - or, in a library, the one where most of the readers gather. Therefore it may turn out that although one access point will be enough to provide full covering of the site, the number of access points should be raised up to two or three - depending on anticipated traffic - because of network efficiency.
If we plan a local network, designated only for office employees, the security problem should be regarded with an utmost care. Chosen access points and wireless cards should be at least WPA standard compatible, or, still better, should allow upgrade to 802.11i standard, when it becomes authorized and launched platform. In case of public network the most trouble area will be the hot spot hardware: ease of new user configuration, billing system, firewalls to prevent hacker attacks, wireless clients separation, and the like.
When we design a wireless network which is to work in a very spacious hall or warehouse, the most difficult thing will be to provide covering of the whole location, especially if machines or racks will attenuate radio signal. In such places the network traffic is scarce, usually limited to one or two employees, who supervise the storeroom or perform production tests. If there are few obstacles, an omnidirectional antenna may be installed in the middle of the hall, for example MA-WO24-8X (A72112). The antenna shouldn't be mounted high, because its vertical half power beam is 25o. It should be remembered that large machines or racks may block covering the entire hall area.
In such a case we should decide where the covering is essential, and install additional access points there. There is no use in sophisticated antenna installations if similar result may be obtained with additional access points. Prices of AP equipment drop down rapidly and such solution may turn out quite cheap and much easier to implement. Using very expensive antennas and multiplexers is the extreme solution - if there is no accessible network infrastructure at the location, you can use WDS mode to connect several access points with one another.
An example of using panel antennas in a storeroom
If we take into regard installing wireless network in such places like lecture halls, our attention should be focused on different problems. Such halls are free of obstacles causing high signal attenuation, as it is in the case of storeroom racks. Designing network for such halls we should pay most of our attention to the network capacity. Usually in such places there is a large number of people and the capacity of network is the priority there.
In such a case, our first step will be to estimate average number of users working simultaneously in the network. One access point may provide access for 20 to 30 users, so if we anticipate a maximum of 70 simultaneous users, we will need three access points. If we anticipate 40 users, two access points will do, and if the maximum number of users is not more than 30, one access point will turn out enough. It must be remembered though, that if more than one access point works in such an area, each one should operate on different channel (for example 1 and 7 for two AP or 1, 6 and 11 for three AP installed).
Next step in installation of a wireless network is the right deployment of transmitters. Of course they should be guarded against unauthorized external access - the most efficient and the simplest solution is to mount them high, near the ceiling. This will protect devices from unauthorized access and provide good covering of the hall.
Wireless network is usually connected to outside world, so when designing it, we should take into consideration the necessity of providing needful cabling to distribution system or to the Internet.
It is very important to use only appropriate equipment. We should decide beforehand whether all users are to have unlimited access to network resources or whether the outside ones are to have access only to a limited set of network services (for example we may grant users access to websites and e-mail, but forbid them using FTP). If we are going to limit services, we should choose devices with the hot-spot feature, that is public access points, as they will grant us control over variety of services provided by our wireless network. But if this aspect is not of utmost importance, we can use cheaper and simpler devices without the filter feature.
Recommended location of access points depending on their number. :
2 AP és 3 AP
Az analóg és digitális televízió adóállomások adatai Lengyelországban. (információk kimondottan a lengyelül beszélő felhasználók számára)... bővebben »
A cikk az integrált telekommunikációs és RF elosztó rendszerek kivitelezési lehetőségeit mutatja be többcsaládos épületekben, melyek megfelelnek az új... bővebben »