MSM Controllers - Wireless Best Practices for high density deployments
Wireless performance and Connection issues -
- Affects Hotels, Schools, Hospitals and Auditorium deployments.
- Affects all MSM Controllers and APs
- Affects High-density AP deployment (commonly in hotels, schools, hospitals, auditoriums)
- Affects all MSM software versions
WIFI deployments in Hotel, School, Hospitals and Auditorium sites are difficult, owing to the need for more APs in closer proximity to each other, to handle a higher client densities (20-40 users per AP in classrooms, auditoriums, cafeterias), as compared to "Enterprise" deployments in office spaces, where client-density would be less, and AP placement is spaced father apart for coverage of a larger floor space, where APs run normally at full TX power.
When the APs are running at full TX power (23db-27db EIRP), and are spaced closer than 8 meters to each other, they generates their own severe RFI (Radio Frequency Interference), and this reduces the received sensitivity of the APs, making it harder to hear clearly the wireless clients. (Other outside sources of RFI are possible, such as other wireless networks, wireless cameras, etc.)
Also, because client devices (iPhones, Android phones, Tablets and other PDAs) do not transmit with much TX power (30mw-50mw), as compared to the stronger laptop counterparts (100mw-200mw), they are much harder to be heard above the Noise Floor (RFI level) and this creates another additional challenge for the AP deployment.
Lastly, the physical site can improve or detract from the noise level and signal quality, depending on the wall and floor (ceiling) materials.
Concrete walls will contain the signals in a given room, (reducing RFI elsewhere), but will not propagate a very good signal outside the room.
Drywall or glass is virtually transparent to radio signals, which means they will propagate further, but at the same time, may interfere with adjacent APs in other rooms.
RRM (Radio Resource Manager) works great in Enterprise environments, where APs are spaced further apart, to calculate and adjust the Channel Plan and Power Plan for the APs, thus minimizing RFI and maximizing coverage. But, RRM cannot handled the extreme power-reduction demands, when APs are less than 8 meters apart and severe RFI is present, such as adjacent classrooms, auditoriums, etc.
Therefore, this article addresses deployments where RRM is unable to contend with the closer proximity of APs and resulting severe RFI, and corrections are needed to balance the WiFi properly.
The primary cause is when the APs are deployed in close proximity to other APs, (i.e. adjacent classrooms), their high power can actually interfere with adjacent APs, making it harder for APs to hear wireless clients. The default is the AP transmissions (23 to 28db EIRP) and are set to maximum power and are not appropriate when APs are so closely spaced (< 10 meters).
- Some client devices don't work well on certain channels on 2.4ghz and 5ghz bands, so you need to exclude certain channels.
- Some clients do not roam aggressively and remain connected to APs they are moving away from them, (Sticky Client Syndrome), so we can set wireless rates to improve roaming.
- RRM (Radio Resource Manager), was designed to work best in office deployments, so it faces some challenges in high-density deployments.
1. Always install the latest MSM Maintenance Release to get all the available fixes and wireless optimizations.
Many of these are either fixes or improvements for the wireless interfaces. (188.8.131.52 as of this writing)
(A software contract is required to be entitled to new software)
2. Disable RRM (Controlled APs --> RRM --> RRM) and un-check all checkboxes.
3. Adjust settings on the Controlled APs-->Radio Management-->Radio Configuration tab and Radio-2, for all models of APs you use;
- For best practices, choose 20 MHz for 2.4ghz band on Radio-2, (default).
- Set channel to Automatic Channel for both radios on Radios-2, (default).
- On Radio-2, (2.4ghz), exclude all channels except 1, 6 and 11. This gives you only non-overlapping channels.
4. Lower radio power and enable Auto-Power to reduce inter-AP interference.
- Disable "Severe Interference Detection and Mitigation".
- Set "Distance between APs" to Medium.
- Lower Radio-2 Transmit Power to 10db-16db. (10db is minimum for most APs)
- Enable "Automatic Power Control" on both radios.
5. On all VSCs, modify the settings to improve client roaming and band selection.
- Enable Broadcast Filter.
- Enable Band Steering. (only if "Broadcast name (SSID)" is also enabled.
- Remove "Allowed Wireless Rates" below 18mbps, leaving 11mbps for 11b enabled.
The goal is to get the Noise Levels reported by clients to show lower Noise Levels between -90db and -100db. This will indicate the reduction in RFI caused by the MSM APs.
However, the MSM APs are NOT the only source of RFI (Radio Frequency Interference), but are the most likely source. Other sources are neighboring APs nearby.
You can verify if other non-MSM APs are causing RFI by going to Controlled APs-->Security-->Neighborhood, and you can sort by SNR.
The SNR column will show you the strongest (and closest) potential interfering non-MSM APs.
APs shown with an SNR above 20 are potentially interfering APs. Unfortunately, we have no control over this APs since they're not ours.