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Understanding Adaptive Channel Planner
Adaptive Channel Planner automatically makes channel-tuning decisions for access point radios on the basis of the RF data gathered by access points. Channel auto-tuning is configured in a Radio profile in Network Director and operates on all access point radios by default. This topic explains channel automatic tuning.
This topic describes:
Why Use Adaptive Channel Planner?
The state of a wireless network is dynamic—to continually tune each access point radio for optimum performance would be time consuming. Auto-tuning performs the following tuning based on feedback from access point scanning:
Chooses a random starting channel for newly deployed access points
Automatically tunes channels of access points to minimize co-channel interference
Mitigates spectral interference
You can specify which channels auto-tuning can choose from.
In addition, auto-tuning maintains tuning configurations across access point and controller reboots. For more information about scanning, see Understanding Wireless Scanning.
When Should I Use Adaptive Channel Planner?
Channel auto-tuning is beneficial in these situations:
When you are deploying a new network—no channel configuration exists yet.
When you add or move access points.
When the performance of an existing configuration needs improvement.
When the network is experiencing interference.
When you need to tune around channels used by radar when there is either weather or military radar operating in your area. Weather radar frequently operates at large commercial airports.
When interference makes a channel unusable. For example, a continuous wave transmitter, like some video surveillance cameras, will make a channel unusable.
Adaptive Channel Planner Improves Performance
Auto-tuning optimizes performance—you do not need to make repeated channel changes in a reactive mode. Channel tuning for performance operates best over a regular time frame, such as a day. We recommend that you schedule auto-tuning to collect data over a long period of time, then make changes at a time when only a few users are affected.
The duration of the sample period must match the retuning period so that the algorithm does not generate a reactive response to short term-transients. For example, the whole network should not retune each time a door opens or closes. Instead, it is better to choose and maintain tuning that takes into account how much of the time the door is open and closed (average samples over a long period). Changing channels can be disruptive to active clients—therefore, it is best not to do it frequently and at times when service disruptions can be tolerated.
Adaptive Channel Planner Resolves Interference
If a channel becomes unusable, the wireless auto-tuning algorithm immediately changes the radio to a working channel but the changes do not persist. The algorithm tries to revert to the configured channel at intervals. This emergency tuning is similar to DFS channel handling.
Adaptive Channel Planner Is Used by Dynamic Frequency Selection to Comply with Country Regulations
If an access point detects radar on a channel it is currently using, regulations require that it cease using the channel immediately. Auto-tune enables the radio to be switched to a usable channel rather than taking the radio out of service.
Dynamic Frequency Selection (DFS) requirements apply only to radios operating in the 5-GHz band (802.11a radios). Auto-tuning enables the system to retune channels in the 5-GHz band when radar is detected and regulations require the system to cease using a channel.
When a controller learns that an access point 802.11a radio has detected radar on a channel, Auto-tune immediately switches the radio to another channel. The event is time stamped along with the state of the channel. For the next 30 minutes, the controller blocklists the radar channel—after this, the channel is automatically added back to the eligible channel list.
If radar is detected on a radio with its Auto-tune channel disabled, the radio goes out of service as required by the Federal Communications Commission (FCC) and European Telecommunications Standards Institute (ETSI).
DFS is configured in a Radio profile—see Creating and Managing a Radio Profile.
How Does Adaptive Channel Planner Work?
The controller evaluates the radios’ scanning results for possible channel changes every 3600 seconds (1 hour). An algorithm running as a distributed algorithm on controllers and access points uses the following parameters to determine whether to change the channel on a radio:
Amount of noise on the channel
Packet retransmission count—see Monitoring the Percentage of RF Packet Retransmissions for more information.
Utilization calculated on the number of multicast packets per second that a radio can send on a channel while continuously sending fixed-size frames over a period of time.
Phy error count, which is the number of frames received by the radio with physical layer errors. A high number of Phy errors can indicate the presence of a non-802.11 device using the same RF spectrum.
Received cyclic redundancy check (CRC) error count. A high number of CRC errors can indicate a hidden node or co-channel interference.
The thresholds for these parameters are not configurable. RF auto-tuning also can change a radio channel when the channel tuning interval expires, if a channel with less disturbance is detected. Disturbance is based on the number of neighbors the radio has and the RSSI of each neighbor. A radio also can change channels before the channel expires to respond to interference or radar.
How Do I Configure Adaptive Channel Planner?
Adaptive Channel Planner is an Advanced Setup option of Radio profiles—see Creating and Managing a Radio Profile. In addition to disabling and enabling Tune Channel, you can change these settings:
Tune Transmit Power
Tune Channel Range (11a)
Channel Tuning Interval
Channel Tuning Holddown
TX Power Backoff Timer
Power Tuning Interval
Power Ramp Interval
For descriptions of these settings and directions for creating Radio profiles, including automatic channel tuning, see Creating and Managing a Radio Profile.
What Are Adaptive Channel Planner Results?
Because auto-tuning automatically optimizes channels used by an access point, the following results occur:
Co-channel interference is minimized. Co-channel interference occurs when multiple neighboring radios use the same frequency (channel). Excessive co-channel interference occurs if a poor channel plan is used. Auto-tune channel optimizes the channel plan such that nearby access points avoid using the same channel.
Spectral interference from non-802.11 devices, such as instruments, microwaves, cordless phones, and surveillance cameras, is mitigated.
The interference domain is defined. An interference domain is a set of radios in a mobile domain that can interfere with one another. Interference domains are temporary and non-configurable.
Tuning is maintained across access point and controller reboots.
Newly deployed access points are assigned a random starting channel. This also happens at the first invocation. The purpose is to quickly choose a reasonable channel rather than waiting for the tuning algorithm to do its next update. It turns out that just choosing random channels for all radios usually results in a reasonably good tuning. The old method of setting the channel to a single default channel guaranteed that the system started at the worst possible tuning—all radios on the same channel.
Keep in mind Bluetooth devices and frequency hopping cordless phones spread their communications over the entire 2.4-GHz frequency band, so it is not possible to avoid them by changing channels. However, they are designed to coexist with other transmitters, so their interference is minimal.
When Is Adaptive Channel Planner Most Beneficial?
The most beneficial time to turn on auto-configuration is when you first deploy your wireless network or after you make significant changes to you network or facilities. Turn on auto-configuration of channels when you:
First deploy your wireless network or after you make significant changes to your network or facilities.
Deploy new access points that have not had channels configured.
Add more access points to an existing configuration or move existing access points, for example during a remodel.
Discover that a neighboring organization deployed or changed a wireless network in close proximity to some of your access points.
Have reason to believe the current tuning is sub-optimal, for example when users experience poor service in certain locations.
During regular network operation, there is usually no need to retune channels frequently. A working network should be in data collection mode most of the time. It is better to configure channel Auto-tune to collect data over a long period of time and then make changes at a time when only a few users are affected. If you do not have a time when disruptions can be tolerated, you might want to run it only occasionally, on demand.
What Happens When Severe Interference Is Detected?
Severe interference usually occurs only when something changes in the interference domain. For example, a neighboring company could reconfigure their wireless channels, or a new source of interference, such as a continuously transmitting video surveillance camera, is deployed.
If RF scanning detects severe interference, auto-tuning immediately chooses a new temporary channel assignment to mitigate the problem. Auto-tuning becomes active, even if you have configured it to wait. If the interference persists, auto-tune takes it into account the next time it retunes channels. In this case, auto-tuning uses the tuning algorithm to change to a usable channel if one is available. Otherwise, the channel will revert back to the previously tuned channel. The difference with auto-tuning done in a crisis is that the emergency changes are not saved, and Auto-tune will periodically try to revert the network to the saved channels. Only changes made by you are saved.