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By Steve Harrison

 

Introduction

This is the sixth in a series of blog posts that focus on wireless technology and security at Cisco Meraki.

The frequency spectrum that wireless networks operate in are shared frequency spectra; this is one of the reasons that Wi-Fi networks are so polite with one another. However, there are many more potential sources of interference, such as Bluetooth and microwave ovens in the 2.4GHz spectrum or medical scanners and radar in the 5GHz spectrum.  

These sources of interference can have a detrimental effect on the usability of wireless networks. Meraki Auto RF is a powerful and automated RF optimization solution that ensures that Meraki APs create the best possible environment for the clients served.  

Listen and Learn

Auto RF is able to do this because all Meraki APs have a dedicated security radio that also provides visual spectrum analysis. The Meraki APs also share this data with the Auto RF algorithm to determine the optimal channel plan and transmit power appropriately. In addition to this, Meraki network administrators can also get access to real-time channel utilization scans from the live tools section of each and every AP, as shown below:

This gives the administrator both instantaneous and historical data about interference sources seen by that particular AP. This listening radio can also be accessed to provide information in an industry-standard format too, which has traditionally only been available on dedicated spectrum analysis tools.

For customers with older Meraki APs without dedicated listening radios, it is possible to configure the access radios so that they periodically stop serving clients and start listening to the RF.  

Automatic for the People

Meraki Auto RF is actually made up of two different elements, Auto Channel and Auto Tx Power.

Auto Channel

Auto channel is enabled by default on Meraki networks but can be turned off if desired. When enabled, the Meraki dashboard follows best practice for channel use, meaning that only the three non-overlapping channels in the 2.4GHz spectrum are available. In the 5GHz spectrum, the channels available to the AP depends on both the country and hence regulatory domain that the AP is installed in and the type of AP, i.e. indoor or outdoor. Additionally the network administrator can choose to exclude DFS channels, which will prevent the AP from having to roam away from a channel if a radar signal is detected. Finally, administrators can also select the default channel width for transmission in the 5GHz band, as 802.11n supports channel widths of 40 MHz and 802.11ac supports channel widths of 80 MHz and up to 160 MHz, although 160 MHz is not suitable for enterprise deployments or supported in the Meraki dashboard.

In order to tune the transmit channel, the APs track the following three things:

  • Usage Demand – APs within the dashboard network are monitored for their usage demand, i.e. the number of clients and amount of traffic being served by the AP. These values are mathematically combined so that each AP has a weighted value. This value is then used to ensure that the cleanest channels are utilized in the most demanding areas.
  • Airtime Availability – Each access point listens to the contention and airtime availability, i.e. free time in the medium, for each channel and bandwidth combination. When this data is aggregated it can be used to maximize the available airtime for all APs in the network, also known as the Basic Service Set (BSS), and also minimizes contention and improves client roaming performance. All visible APs — even neighboring APs — are considered in this metric, with Meraki APs being weighted higher to optimize roaming and airtime usage distribution. As opposed to just being polite (i.e. presuming they have as high a priority to the airtime as the Meraki AP and they’re clients)  with respect to neighboring networks and APs, this metric ensures that the AP and its clients also have ample airtime availability.
  • Channel Utilization – This metric includes both 802.11 and non-802.11 (Bluetooth, microwave ovens, etc.) sources of spectrum utilization. These external sources of interference are detected and accounted for within this metric.

The dashboard uses this information to tell the APs to move to a different channel if, say, a new AP is added, a channel becomes jammed, or the network administrator clicks the “Update Auto Channels” button.  

Channel moves can also be triggered by the “Steady State” process, which runs every 15 minutes. The Steady State process will instruct the AP to move channels if a better channel, based on the above criteria exists. However, the Steady State process is aware when a channel is being used for point-to-point communications and it will not change the channels of APs acting as a gateway AP.  

Auto Tx Power

Auto Tx Power operates by sampling the signal-to-noise ratio of neighboring APs in the same network. These readings are compiled into neighbor reports that are sent to the dashboard for processing. All AP neighbor reports are then aggregated and the dashboard leverages that aggregated data to determine each AP’s direct neighbors — APs that clients being served by the AP are likely to roam to — and how much each AP should adjust its transmit power to optimize cell coverage. The dashboard completes this calculation and instructs the APs to adjust their respective transmit power once every 20 minutes.  

As with Auto Channel, Auto Tx Power is mesh-aware and the same Steady State process/algorithm prevents power adjustments for APs that are acting as a gateway for an active mesh repeater.

Conclusion

Meraki’s Auto RF technology auto-tunes the RF for all but the most particular RF environments, and it does so without any need for additional appliances, services or licenses, by leveraging the power of the power.

References

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