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Adaptive Radio Management
Adaptive Radio Management (ARM) is an RF management technology for a stable, self-healing RF
design. ARM takes the distributed algorithm approach, allowing APs to determine their transmit power
and channel settings based on what they detect. The APs make their channel and power setting
decisions based on the RF environment as they hear it, independent of the WFS709TP. This results in a
highly scalable and reliable RF environment, while also significantly reducing the time the AP takes to
adapt to changes in the RF environment.
The APs scan all valid channels in the regulatory domain at regular intervals and compute the following
metrics per channel:
• Coverage index: Signal-to-noise ratio for all valid APs
• Interference index: Signal-to-noise ratio for all APs
These metrics are used by the APs and AMs to determine the channel and transmit power settings for
optimal coverage.
ARM, if enabled, is a continuous process that works on real-time. It allows the system to detect changes
in the RF and to dynamically react to maintain the most optimized RF system possible.
Advantages of Using ARM
Using ARM provides the following benefits:
• The WFS709TP does not require a downtime for initial calibration.
• The AP response time to noise is quick and reliable, even to non-802.11 noise, especially when
client traffic starts generating errors due to the noise.
• Non-802.11 noise detection is disabled by default and must be explicitly enabled.
• The ARM algorithm is based on what the AP hears, which means that the system can compensate
for scenarios like broken antennas or blocked signal coverage on neighboring APs.
• Since channel decisions are based on the information the AP receives from the RF environment,
interference due to third-party APs is taken into account.
How ARM works
The Access Points constantly scan other channels during dead intervals.
1. Access Points analyzes BSSIDs and interference seen on channels currently in use, as well as
other channels.
2. Access Points reports back to switch when a better channel is found. (“Better” is defined as “least
number of APs seen on a channel” or “better SNR statistics”)
4. Switch analyzes reports from APs and makes calculations based on known WLAN topology
database.
5. If switch finds no conflicts, it will instruct AP to move to the new channel.
6. Dampening factor prevents channel “flapping”.
Enabling ARM
ARM Assignment Options
1- Disabled: Disables ARM calibration and reverts APs back to default channel and power settings.
2- Single Band: Enables the APs to change channels, in same band, and transmit power.
3- Multi Band: Currently not supported (for future use, selecting Multi Band automatically sets the
selection to Single Band)
4- Maintain: Causes APs to hold last used channel and power settings. Useful for customers
concerned with APs changing channel/power during use.
ARM Options
1- ARM Scanning: Enable ARM Scanning.
2- ARM Client Aware: Prevents AP from changing channel if clients are associated.
3- ARM Rogue AP Aware: If no other APs are on the same channel as the Rogue or no AM are
available the AP can change channel to contain a Rogue. An AP can always contain a rogue on
the same channel.
4- ARM VoIP Aware: Pauses ARM Scanning when a VoIP call is detected (SIP, SCCP, SVP,
Vocera)
5- ARM Multi Band Scan: Allows APs to scan across bands for Rogue detection. Should not be
enabled for dual band APs.
Best Practices:
1- ARM Scanning: Enabled.
2- ARM Client Aware: Disabled. Otherwise, AP cannot recalibrate around interference.
3- ARM Rogue AP Aware: optional. AP will change channel to contain a rogue AP. APs will
perform containment on-channel by default. AMs are still recommended for Rogue Containment.
4- ARM VoIP Aware: Enabled.
Power Level Adjustments
The radio power levels in the Netgear Wireless Switch are adjustable between 0 and 4, 0 being the
lowest value possible and 4 the highest.
Power assignment decisions are based on the AP’s coverage index. The benchmark used here is the
ideal-coverage index. The ideal-coverage index is the power setting that an AP should have for good
coverage. It is a configurable parameter on the WFS709TP.
The AP increases or decreases 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 or
decrement by a single unit at any given time.
Likewise, if an AP fails, the power levels will be dynamically adjusted to fill in holes.
Power levels:
802.11B/G Band:
Level dB mW
0 0 1
1 11 13
2 14 25
3 17 50
4 20 100
802.11A Band:
Level dB mW
0 0 1
1 9 8
2 12 16
3 15 32
4 18 63
Channel Selection
APs operate most efficiently when they are the only AP on the channel. One of the tasks of the calibration
process is to choose channels to minimize channel overlap, as overlapping channels can corrupt data
transmissions by creating an “RF Collision”
Channel assignments vary by country due to localized regulations. Also, administrators can change which
channels will be used by the system.
In addition to the interference index, the APs use the free-channel index to determine the optimal channel
setting. The free-channel index is a configurable parameter on the WFS709TP used by an AP to qualify a
channel before moving to it. An AP chooses 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 this requirement is not met, the AP remains on the current channel.
BEFORE CALIBRATION
When deploying APs, they will use default power and channel values as shown on the following picture.
Left in this condition, the system would not be very functional.
Here, all .11a radios on channel 36, all .11g radios on channel 1 and all power levels are at 50%
AFTER CALIBRATION
After calibration, the APs change channel assignments and modify power levels to provide a non-
overlapping system. Although this image shows “white areas” without coverage, that is not really the
case. The heat plans display coverage at specific transmission rates. You can change the rate to display
on the heat plan. The highest rates will not have as much coverage as lower data rates.
APPENDIX 1 – Note on Air Monitors
When ARM is enabled, AP’s will sample other channels to search for IDS policy violations (Rogue AP’s,
etc).
Air Monitors offer the capability to perform Advanced IDS scanning and remote packet capture on any
channel.
Following is a list of AM features available when WGL102/WAGL102 is running in AP mode with scanning
enabled:
- Wireless RMON stats for the channel AP is on.
- Packet Capture for the channel AP is on.
- Rogue detection/classification on all channels.
- STA classification on all channels.
- Signature analysis like Netstumbler/asleap/void11 on all channels.
- IDS Rate Analysis on the channel AP is on.
- IDS MAC OUI check for all channels.
- EAP Rate Analysis on the channel AP is on.
- Adhoc/Bridge detection on all channels.
- Threshold event generation on the channel AP is on.
- Interference detection on the channel AP is on.
- AP misconfiguration detection on all channels (Interfering AP Broadcasting an ESSID owned
by the Netgear Wireless).
- Fake AP flood detection on the channel AP is on.
APPENDIX 2 – Note on IRM
Early version of the manual list ARM as IRM, this is in reference to exactly the same feature and can be
considered errata. New versions of the manual, available online, have this mistake corrected.
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