Channel Management
The following Channel Management topics are covered here:
Navigating to Channel Management
To view session monitoring information, click the Cluster > Channel Management tab.
Understanding Channel Management
When Channel Management is enabled, the Devicescape Reference AP automatically assigns radio channels used by clustered access points to reduce mutual interference (or interference with other access points outside of its cluster). This maximizes Wi-Fi bandwidth and helps maintain the efficiency of communication over your wireless network.
(You must start channel management to get automatic channel assignments; it is disabled by default on a new AP. See Stopping/Starting Automatic Channel Assignment.)
How it Works in a Nutshell
At a specified interval (the default is 1 hour) or on demand (click Update), the Channel Manager maps APs to channel use and measures interference levels in the cluster. If significant channel interference is detected, the Channel Manager automatically re-assigns some or all of the APs to new channels per an efficiency algorithm (or automated channel plan).
For the Curious: More About Overlapping Channels
The radio frequency (RF) broadcast Channel defines the portion of the radio spectrum that the radio on the access point uses for transmitting and receiving. The range of available channels for an access point is determined by the IEEE 802.11 mode (also referred to as band) of the access point.
IEEE 802.11b/802.11g modes (802.11 b/g) support use of channels 1 through 11 inclusive, while IEEE 802.11a mode supports a larger set of non-consecutive channels (36,40,44, 48, 52, 56, 60, 64, 149, 153, 157, 161, 165).
Interference can occur when multiple access points within range of each other are broadcasting on the same or overlapping channels. The impact of this interference on network performance can intensify during busy times when a large amount of data and media traffic is competing for bandwidth.
The Channel Manager detects which bands (b/g or a) clustered APs are on, and uses a predetermined collection of channels that will not mutually interfere. For the "b/g" radio band, the classical set of non-interfering channels is 1, 6, 11. Channels 1, 4, 8, 11 produce minimal overlap. A similar set of non-interfering channels is used for the "a" radio band, which includes all channels for that mode since they are not overlapping.
Example: A Network Before and After Channel Management
Without automated channel management, channel assignments to clustered APs might be made on consecutive channels, which would overlap and cause interference. For example, AP1 could be assigned to channel 6, AP2 to channel 6, and AP3 to channel 5 as shown in Figure 1.
Figure 1 Without Automatic Channel Management: APs Can Broadcast on Overlapping Channels
With automated channel management, APs in the cluster are automatically re-assigned to non-interfering channels as shown in Figure 2.
Figure 2 With Channel Management Enabled: APs are Re-Assigned to Non-Interfering Channels
Configuring and Viewing Channel Management Settings
The Channel Management page shows previous, current, and planned channel assignments for clustered access points. By default, automatic channel assignment is disabled. You can start channel management to optimize channel usage across the cluster on a scheduled interval.
From this page, you can view channel assignments for all APs in the cluster, stop/start automatic channel management, and manually "update" the current channel map (APs to channels). On a manual update, the Channel Manager will assess channel usage and, if necessary, re-assign APs to new channels to reduce interference based on the current Advanced Settings.
By using the Advanced settings you can modify the interference reduction potential that triggers channel re-assignment, change the schedule for automatic updates, and re-configure the channel set used for assignments.
The following sections describe how to configure and use channel management on your network:
Stopping/Starting Automatic Channel Assignment
By default, automatic channel assignment is disabled (off).
- Click Start to resume automatic channel assignment.
When automatic channel assignment is enabled, the Channel Manager periodically maps radio channels used by clustered access points and, if necessary, re-assigns channels on clustered APs to reduce interference (with cluster members or other APs outside the cluster).
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Note
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Channel Management overrides the default cluster behavior, which is to synchronize radio channels of all APs across a cluster. When Channel Management is enabled, the radio Channel is not synced across the cluster to other APs. See the note under Radio Settings in Settings Shared in the Cluster Configuration.
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- Click Stop to stop automatic channel assignment. (No channel usage maps or channel re-assignments will be made. Only manual updates will affect the channel assignment.)
Viewing Current Channel Assignments and Setting Locks
The "Current Channel Settings" shows a list of all access points in the cluster by IP Address. The display shows the band on which each AP is broadcasting, the current channel used by each AP, and an option to "lock" an AP on its current radio channel so that it cannot be re-assigned to another. Details about Current Channel Settings are provided below.
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Field
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Description
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IP Address
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Specifies the IP Address for the access point.
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Radio
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Indicates the MAC address of the access point.
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Band
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Indicates the band (b/g or a) on which the access point is broadcasting.
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Channel
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Indicates the radio Channel on which this access point is currently broadcasting.
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Locked
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Click "Locked" if you want this access point to remain on the current channel.
When the "Locked" checkbox is checked (enabled) for an access point, automated channel management plans will not re-assign the AP to a different channel as a part of the optimization strategy. Instead, APs with locked channels will be factored in as requirements for the plan.
If you click Update, you will see that locked APs show the same channel for "Current Channel" and "Proposed Channel". Locked APs will keep their current channels.
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Update Current Channel Settings (Manual)
You can run a manual channel management update at any time by clicking Update under the Current Channel Settings display.
Viewing Last Proposed Set of Changes
The Last Proposed Set of Channel Changes shows the last channel plan. The plan lists all access points in the cluster by IP Address, and shows the current and proposed channels for each AP. Locked channels will not be re-assigned and the optimization of channel distribution among APs will take into account the fact that locked APs must remain on their current channels. APs that are not "Locked" may be assigned to different channels than they were previously using, depending on the results of the plan.
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Field
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Description
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IP Address
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Specifies the IP Address for the access point.
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Current
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Indicates the radio channel on which this access point is currently broadcasting.
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Proposed
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Indicates the radio channel to which this access point would be re-assigned if the Channel Plan is executed.
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Configuring Advanced Settings (Customizing and Scheduling Channel Plans)
If you use Channel Management as provided (without updating Advanced Settings), channels are automatically fine-tuned once every hour if interference can be reduced by 25 percent or more. Channels will be re-assigned even if the network is busy. The appropriate channel sets will be used (b/g for APs using IEEE 802.11b/g and a for APs using IEEE 802.11a).
These defaults are designed to satisfy most scenarios where you would need to implement channel management.
You can use Advanced Settings to modify the interference reduction potential that triggers channel re-assignment, change the schedule for automatic updates, and re-configure the channel set used for assignments.
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Field
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Description
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Advanced
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Click "Advanced" toggle to show / hide display settings that modify timing and details of the channel planning algorithm.
By default, these settings are hidden.
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Change channels if interference is reduced by at least
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Specify the minimum percentage of interference reduction a proposed plan must achieve in order to be applied. The default is 25 percent.
Use the drop-down menu to choose percentages ranging from 25 percent to 75 percent.
This setting lets you set a gating factor for channel re-assignment so that the network is not continually disrupted for minimal gains in efficiency.
For example, if channel interference must be reduced by 75 percent and the proposed channel assignments will only reduce interference by 30 percent, then channels will not be re-assigned. However; if you re-set the minimal channel interference benefit to 25 percent and click "Update", the proposed channel plan will be implemented and channels re-assigned as needed.
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Determine if there is better set of channel settings every
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Use the drop-down menu to specify the schedule for automated updates.
A range of intervals is provided, from "1 Minute" to "6 Months".
The default is "1 Hour" (channel usage re-assessed and the resulting channel plan applied every hour).
Note: Keep in mind that every time the channel planner is triggered, the AP's operating channel may change and clients will have to re-associate. Therefore, setting the planning interval for less than an hour can destabilize wireless access for clients.
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Use these channels when applying channel assignments
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Choose a set of non-interfering channels on a particular band ("b/g" or "a"). The choices are:
- b/g channels 1-6-11
- b/g channels 1-4-8-11
- a
IEEE 802.11b/ 802.11g modes (802.11 b/g) support use of channels 1 through 11. For the "b/g" radio band, the classical set of non-interfering channels is 1, 6, 11. Channels 1, 4, 8, 11 produce minimal overlap.
IEEE 802.11a mode supports a larger set of non-consecutive channels (36,40,44, 48, 52, 56, 60, 64, 149, 153, 157, 161, 165). All "a" band channels are non-interfering.
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Apply channel modifications even when the network is busy
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Click to enable or disable this setting.
If a checkmark appears, this indicates the option is enabled and channel modifications will be applied even when the network is busy.
If this is not checked, channel modifications will not be applied on a busy network.
This setting (along with the interference reduction setting) is designed to help weigh the cost/benefit impact on network performance of re-assigning channels against the inherent disruption it can cause to clients during a busy time.
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Update Advanced Settings
Click Update, under Advanced settings, to apply these settings.
Advanced settings will take affect when they are applied, and influence how automatic channel management is performed. (The new interference reduction minimum, scheduled tuning interval, channel set, and network busy settings will be taken into account for automated and manual updates.)
