Airlogic ABM-400 Manual de usuario descargar pdf (Pagina 38)

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A typical Wi-Fi setup contains one or more Access Points (APs) and one or more clients. An AP

broadcasts its SSID (Service Set Identifier, "Network name") via packets that are called beacons,

which are usually broadcast every 100 ms. The beacons are transmitted at 1 Mbit/s, and are of

relatively short duration and therefore do not have a significant effect on performance. Since 1

Mbit/s is the lowest rate of Wi-Fi it assures that the client who receives the beacon can

communicate at least 1 Mbit/s. Based on the settings (e.g. the SSID), the client may decide

whether to connect to an AP. If two APs of the same SSID are in range of the client, the client

firmware might use signal strength to decide which of the two APs to make a connection to. The

Wi-Fi standard leaves connection criteria and roaming totally open to the client. This is a

strength of Wi-Fi, but also means that one wireless adapter may perform substantially better than

the other. Since Wi-Fi transmits in the air, it has the same properties as a non-switched ethernet

network. Even collisions can therefore appear as in non-switched ethernet LAN's.

Except for 802.11a, which operates at 5 GHz, Wi-Fi uses the spectrum near 2.4 GHz, which is

standardized and unlicensed by international agreement, although the exact frequency allocations

vary slightly in different parts of the world, as does maximum permitted power. However,

channel numbers are standardized by frequency throughout the world, so authorized frequencies

can be identified by channel numbers.

The frequencies for 802.11 b/g span 2.400 GHz to 2.487 GHz. Each channel is 22 MHz wide yet

there is a 5 MHz step to the next higher channel.

The maximum number of available channels for wi-fi enabled devices is 13 for Europe, 11 for

North America and 14 for Japan. A wireless access point (AP) connects a group of wireless

stations to an adjacent wired local area network (LAN). An access point is similar to an ethernet

hub, but instead of relaying LAN data only to other LAN stations, an access point can relay

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Airlogic ABM-400 Manual de usuario Pagina 38