Aruba Networks AirOS v2.3, User Manual

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48 Aruba AirOS Part 0500036-02
v2.3 User Guide January 2005
setting decisions independent of the switch and based on the RF environment as they hear it.
This results in a highly scalable and reliable RF environment while also significantly reducing
the AP’s reaction time to the network.
The APs scan all valid channels (channels in the regulatory domain) at regular intervals and
compute the following metrics per channels -
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Coverage index : signal to noise ratio for all valid APs
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Interference index : signal to noise ratio for all APs
These metric are used by the APs to decide the best channel and transmit power settings for
optimal coverage.
Deciding the Channel Setting
In addition to the interference index, the APs use the free-channel index for deciding the
optimal channel setting. The free-channel-index is configurable parameter on the switch used
by an AP to qualify a channel before moving to it. An AP will choose to move to a new channel
only if its current channel interference index is greater than the interference index on the new
channel by a value greater than or equal to the free-channel index. If the criteria are not met
the AP will remain on the current channel.
Deciding Power Settings
The power assignment decisions are based on the APs coverage index. The benchmark used
here is the ideal coverage index. The ideal-coverage index is the ideal power setting that an AP
should have for good coverage. It is a configurable parameter on the switch. The AP will
increase or decrease its power settings based on the difference between the value of its current
channel coverage index and the ideal-coverage-index value. The power settings increment /
decrement by a single unit at any given time.
Advantages of Using ARM
Using ARM provides the following benefits:
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With ARM, the switch does not have a downtime for initial calibration. Though this pro-
cess is still optional, it is no more a necessity.
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The AP response time to noise is quick and reliable, even the non-802.11 noise.
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ARM algorithm is based on what the AP hears which means that the system can compen-
sate for scenarios like broken antenna and blocked signal coverage on neighboring APs.