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airMAX - Frequently Asked Questions (FAQs)

What is the maximum number of clients that can connect to airMAX M series and airMAX AC Access Points?

  • M:  127
  • AC: 85
  • AC (with GPS Sync enabled): 60 
  • 2AC: 50

What is the effective throughput difference between airMAX M series & airMAX AC series?

In contrast to airMAX M series devices (built on 802.11n protocol), airMAX AC devices benefit greatly from physical-layer & MAC-layer efficiencies associated with 802.11ac protocol. The following image below outlines the maximum throughput related to each network type at various modulation rates , where greenfield AC networks (i.e. exclusively AC devices) enjoy the greatest benefit:


When retrofitting legacy networks, it is therefore always recommended that you upgrade the AP device first to experience the most initial benefits. Note too that M series devices cannot each the 8x MCS rates enjoyed by AC series devices.

What is airMAX Priority?

airMAX Priority is a Station-side setting available with airMAX M & AC networks, that defines the number of time slots (i.e., ratio of airtime allocated to a Station device) manually allocated by the AP. By default, the AP grants equal time slots (i.e., same airtime ratios) to all active Stations. When configured with different priorities, the AP grants Stations more or less time slots (i.e., airtime), depending on the airMAX Priority value. For best performance on the airMAX network, the Stations with the best signals should receive the higher priorities (i.e., more airtime), while Stations with poorer signals should receive less/no priority (i.e., less airtime). When properly configured, the net effect increases the overall performance/throughput of the airMAX network. This is because strong SNR clients (i.e., Stations with highest throughput efficiency) configured with higher airMAX priority values will access to more of the AP’s airtime, increasing the overall airMAX network speed/performance.

For most users, leaving airMAX Priority settings at their default values is generally recommended. Moreover, configuring airMAX Priority values is only recommended in certain situations, like with Weakest Link client scenarios (i.e., one or more weak clients dragging down the airtime of the entire airMAX network). In such cases, properly configured airMAX Priority values can result in higher possible throughput and lower latency among active clients. 


Note: While most users are recommended to leave airMAX Priority to their default values, these settings can be changed by clicking on the airMAX logo tab (for M series devices) or the Wireless tab (for AC devices).

airMAX Priority (airMAX AC) options include:

High 4:1 (4 time slots) Suggested for clients with best/highest SNR
Medium 3:1 (3 time slots) Suggested for Stations with above average SNR
Base 2:1 (2 time slots) Default setting for Stations
Low 1:1 (1 time slot) Suggested for Stations with poorest/lowest SNR

Note: If all Stations are configured with the same airMAX Priority value (ex. High), then the net effect remains equal (as if default values were used).

What is airMAX Capacity (AMC) & airMAX Quality (AMQ)?

In airMAX M series networks, airMAX Capacity (AMC) represents airtime efficiency. For example, if you have one Station with a low data rate or you are using a 1x1 device (such as Bullet or airGrid) alongside other Stations that are 2x2, then it will use up more airtime (time slots) for the same amount of data, reducing time (or capacity) for other Stations. The lower the AMC, the less efficient the access point (AP) is. If you only have one client, this may not matter, but when you have many clients (for example, more than 30), then AMC becomes very important, and you want it to be as high as possible. airMAX Quality (AMQ) represents the number of retries, as well as the quality of the physical link. If this value is low, you may have interference and need to change frequencies. If AMQ is above 80% and you do not notice any other issues, then you do not need to make any changes.

When examining a client-side airMAX device, AMC shows the theoretical capacity of that client, based on current TX/RX rates and quality. AMC relates the percentage based on what maximum performance would be if the link were perfect. Stations with poor airtime efficiency can negatively affect other Stations by taking up more airtime while transmitting at lower speeds. For example, client A is at MCS 12 (78 Mbps) because of low signal. The client could theoretically negotiate at MCS 15 (130 Mbps), so AMC is based on the ratio of current rate/maximum rate (78 Mbps divided by 130 Mbps), which is 60%. In a similar fashion, a 1x1 device will always have a maximum AMC of 50%, because it provides half the performance of a 2x2 device.

When examining the AP, then AMQ and AMC are averages of all clients’ values. If you want to discover what is lowering your values on heavily populated APs, identify the weakest signal clients using the UISP management platform. It is also recommended that you upgrade to higher-gain antenna to improve signals bidirectionally, and thus allow for better data rates.

Low CCQ; what is it and how to make it better?

Low CCQ is a direct indicator of lost packets which might be due to the fact that there might be interference. Here are some suggestions to improve it: 
  • Make sure that the units are properly aligned.
  • Check for noise in the area and select the channels accordingly
  • If there is a lot of noise, consider reducing the channel width of change the channel
  • Make sure that you have a clear line of sight
  • Make sure that the distance is set to auto (Advance Tab)

What is the difference between Router and SOHO Router mode?

  • In Router Mode, the WAN interface is the wireless interface, and the Local LAN interface is the Ethernet port.
  • In SOHO Router mode, this is reversed so that the WAN interface is the Ethernet port and the Local LAN is the Wireless interface.

Even though the hardware allows these high numbers of clients, that does not mean that you should plan on connecting that many clients to one Access Point. The maximum capacity of an AP is determined by channel width, signal, and noise. Any PTMP product is based on the assumption that not all clients require maximum capacity at the same time.

Which radios support UNII1, UNII2 and UNII3 bands?

All of our 5GHz devices support UNII1, UNII2, and UNII3. Your country’s laws and regulations will either allow or disallow you to uses these bands.

What is the range of airMAX devices?

The range of airMAX devices can vary greatly. To know what device you should use for your installation, you should always use our online link simulator software, found at ispdesign.ui.com.

What is airSelect?

To use airSelect, the user selects a list of frequencies, and the AP will cycle through each selected frequency in order to avoid interference. It records the noise floor of each frequency and spends more time on the best frequency. This feature is only used in very uncommon situations and is rarely recommended to most consumers.

What is the best signal strength and noise floor?

  • You want your signal to always be between a -45 and -65 dBm.
  • Signals that are “too hot” -40dBm or greater can increase EVM and reduce performance.  These should be indicated in red on the APs Station List (AC)
  • The way to decide what signals you need is to look at the Signal to Noise Ratio, also known as SNR. For best performance, we recommend an SNR of at least 25 but preferably 30 or greater. So, if you have a noise floor of -90 dB, you will need to have at least a -65 signal.

When should Long Range PtP Link Mode be enabled?

In airMAX M series outdoor networks, Stations send acknowledgment frames (ACK) after receiving a data frames. However, with longer link distances, it becomes necessary to disable the ACK mechanism. The distance at which the Long Range PtP Link Mode (or PtP noack mode in older versions) should be enabled depends on configured channel width, as listed below:

Channel Width (MHz) Distance (miles / km)
40 16.5 / 26.5
20 35.6 / 57.3
10 72.3 / 116
5 144.7 / 232.9

Note: Enable the Long Range PtP Link Mode (PtP noack mode in older versions) in the airMAX tab, under Settings.


In Point-to-Point (PTP) mode, airMAX AC devices will automatically switch from hardware ACK to software ACK (NOACK), with no configuration required. In Point-to-Multipoint (PtMP) mode however, NOACK isn't supported as such, and there will be distance limitations (see below).

PTMP Mode Distance Limitations


Distance Limit

20/40/80 MHz 22.5 km (14 mi)
30/60 MHz 15 km (9.3 mi)
50 MHz 18 km (11.2 mi)
10 MHz 37.5 km (23.3 mi) 

Note: As of v8.3 we have added Fixed Frame support. Please see this GPS Sync FAQ article for more details on FF distance limitations.

Should I enable Wireless Distribution System (WDS) on a Point-to-Point (PtP) link?

Yes, if both radios are Ubiquiti. While there are some other manufacturers who use WDS that is compatible with Ubiquiti radios, WDS can vary depending on the manufacturer. enabling WDS on bridged links is always recommended. WDS is not designed to interoperate between radio vendors, so by using two Ubiquiti radios, users can pass virtually all traffic across wireless links. To enable WDS, follow the steps below:
  1. Navigate to the Wireless tab of the AP/Station radio.
  2. Check the WDS box, then click on  Change and Apply the settings.
  3. Do the same for the AP.

Note: All airMAX AC radios have WDS enabled by default, and it cannot be disabled. The steps above apply to M devices only.

Why would I use the IsoStation or PrismStation?

Both the IsoStation and the PrismStation have four different antenna options.

  • Asymmetrical 90°
  • Asymmetrical 60°
  • Symmetrical 45°
  • Symmetrical 30

Signal range is up to 5+ km (3+ miles) for both. The only difference between the two is the PrismStation has airPrism and GPS for better co-location. The IsoStation is a less expensive alternative for deployments that do not need as much isolation.

Asymmetrical horn antenna options (60° and 90°) have naturally attenuated side lobes and extremely low back radiation, and they offer industry-leading front-to-back ratio and low side lobe radiation. Symmetrical horn antennas (30° and 45°) are ideal for cluster sector installations with high co-location requirements.

What is airPRISM?

As an AP-side filter technology, airPrism isolates signals within the operating channel to increase capacity and throughput in co-location deployments. Given its wider beamwidth antenna (which causes it to “hear” signals from many other transmitters), APs typically suffer most from in-band interference. This issue isn’t as common at the CPE because they are normally lower to the ground with a much tighter beam-width. airPrism radios may be used with non-airPrism antennas and still benefit from the airPrism radio-side filter technology, but airPrism antennas feature more robust RF shielding (especially beneficial in co-location deployments). 

Why am I seeing an SSL Certificate Security Alert when browsing to my device page?

Users may encounter a page stating: "Your connection is not private" with the error: ERR_CERT_AUTHORITY_INVALID. This is because airOS comes by default with HTTPS enabled (instead of HTTP), so users will see that security alert when they access the unit's Web UI. This doesn't compromise the device's security in any way, and you can safely click on Advanced and proceed to the IP address.

If you wish to avoid the alert, you may disable HTTPS on the services tab. However, disabling HTTPS will cause all traffic destined to the web interface of the airMAX device to be unencrypted, allowing user credentials to be compromised via a packet capture. Ubiquiti does not recommend this. Alternatively, if you have 10 (ten) or more UISP compatible devices, you can adopt them to a free cloud instance of UISP to monitor and managed without SSL warnings.

How to Re-Enable HTTP Server/Service on my airMAX device?

The HTTP/HTTPS services are what allow users to configure airMAX units from the web browser (GUI). If these services are disabled by mistake, users can be temporarily locked out of the radio until they regain access via SSH. Follow the steps below to re-enable the HTTP service via SSH.

  1. Verify that access is not possible through both http://<ip_of_radio> and https://<ip_of_radio>, in case only one of the two web servers was disabled.
  2. If access is still prohibited, connect to the units via SSH.
  3. Now edit /tmp/system.cfg using vi (text editor):
    vi /tmp/system.cfg
  4. Once the file is open, press the insert key on the keyboard, find the line "httpd.status=disabled" and change to:
  5. To save these changes, press the escape key, type :wq and press the enter key like so:
  6. To make these changes persistent and remain after reboot, issue these commands:
    cfgmtd -f /tmp/system.cfg -w
  7. Power-cycle the unit or type:

Note: Alternatively, WinSCP can be used to download /tmp/system.cfg from the radio and edit the file locally. After that, it can be uploaded to /tmp/ where it will overwrite the existing system.cfg file. Then continue from Step 6.

What is Enhanced TX Modeling?

Advanced TX modeling models the effects of TX induced EVM limitations often due to excessive TX power.
By default, airLink takes the numbers you input and shows you the theoretical capacities. But, due to the EVM(Error Vector Magnitude), you may be overdriving the conducted power. So, Enhanced TX Modeling takes the EVM into consideration and gives you a more literal link capacity.

How does airMAX handle QoS & Traffic Prioritization?

QoS is enabled automatically in airMAX devices so there is no configuration necessary to enable QoS. In order for the devices to prioritize traffic properly, the traffic will need to have the 802.1p/DSCP/ToS value correctly configured prior to the traffic entering the airMAX equipment. The originating software or hardware device is responsible for applying these values, and only if these fields are set will traffic be prioritized in accordance with the traffic categories table below.

airMAX equipment supports three levels of priority: high, medium and low. These priority levels are exclusive priority queues; for example, all high traffic will be transmitted before any medium priority traffic, and so on. It is recommended that voice traffic be kept on the high priority queue, with high priority data traffic using the medium priority queue, and other applications configured to use low priority. By default, all traffic is classified as low priority, meaning there is no specific prioritization applied. The other categories can be defined with the following values:

802.1p Class of Service

TOS Range

DSCP Range

Traffic Category

0 - Best Effort



Medium Priority

1 - Background



Low Priority

2 - Spare



Low Priority

3 - Excellent Effort


24-25, 28-31

Medium Priority

4 - Controlled Load



Medium Priority

5 - Video (<100ms latency)



Medium Priority

6 - Voice (<10ms latency)

0x68, 0xb8

26-27, 46-55

High Priority

7 - Network Control



High Priority

Note: 802.1p/ToS/DSCP values which are not included in the above table are used for internal airMAX equipment control purposes.

How to Disable Wireless Security on airMAX AC Devices?

The default security configuration for AC devices since firmware version 8.5.11 was changed to WPA2 AES with a pre-shared key 0000:0000. For users and operators who do not use wireless security on their AP radios, this can cause a network disruption when this setting is not matched by all client radios. The None option was removed from the UI, so the following steps explain how to configure via CLI:

  1. Access the radio command line by your preferred method. SSH is the most common way, and available on any platform. For Windows, the most popular SSH client is PuTTY but you can also use the Windows Subsystem for Linux. On macOS & Linux, OpenSSH is almost always installed by default for use in the terminal emulator. A nice alternative is through the UNMS dashboard.
  2. Edit /tmp/system.cfg manually, with `vi /tmp/system.cfg`. The key-value pair you're looking for is `aaa.status=enabled`. Edit the value to disabled and save the file.
  3. Back on the command line, execute the command `save`.
  4. After following the steps above, your AP will now have wireless security disabled. Confirm this by logging into the Web UI of the radio and checking the Wireless tab of the configuration. This will allow client radios with no security to re-associate with the AP radio, so you can update their configurations to add WPA2-AES encryption.

When an AC radio is reset due to a variety of factors, such as a power surge or short in the cable sending power to the reset pins, up to date AC devices will not have the option in the UI to set Security to None. For networks that do not employ wireless security, this will cause clients to fail the WPA handshake and result in a network disruption.

How to enable DHCP Options?

Starting with airOS v6 and v8, DHCP options are now available for both airMAX M & AC series devices. The steps to enable DHCP options follow below:

  1. Download the current radio config from System > Back Up Configuration.
  2. Open the .cfg backup in a text editor like Notepad++ or Brackets.
  3. Navigate to the DHCP section.
  4. Add these lines:
    • dhcpd.1.option.1.status=enabled
    • dhcpd.1.option.1.id=[option number]
    • dhcpd.1.option.1.value="[ip address]"
  5. dhcpd.1.option.1.status enables or disables DHCP options
  6. dhcpd.1.option.1.id allows you to select what option you choose to use. The configuration supports values from 0-255. Only add the number of the option you wish to use. Do not include the brackets.
  7. dhcpd.1.option.1.value allows you to select the value you wish to provide with the option you are passing. You must use quotation marks around the value, but do not include the brackets.
  8. Save the changes made to the CFG backup in your text editor and upload to the radio.  System > Upload Configuration.

Where can I find 7.1RC?

If you have a unit on 7.0.3, you will need to upgrade to 7.1RC before updating to the latest stable firmware. Download 7.1-RC Transition firmware.

Does airMAX support connections with standard WiFi?

AC series devices do not connect with non-airMAX devices. M series devices in Station mode can connect to standard Access Points. In Access Point mode with the airMAX protocol disabled, these units will broadcast a signal to which standard 802.11 Wi-Fi devices can connect.

Note: The airMAX protocol can be toggled in the leftmost tab marked with the Ubiquiti logo. This option is only available for M series devices in Access Point mode.

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