OpenWRT Boot Times Affected by WiFi: Difference between revisions

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== OpenWRT Regulatory Database Flag Summary ==
== OpenWRT Wireless Regulatory Flags ==


This section summarizes common Linux/OpenWRT wireless regulatory database flags used after a frequency range entry.
OpenWRT uses the Linux wireless regulatory database to decide which channels, channel widths, and transmit powers are allowed for a selected country code.


Typical rule format:
A regulatory rule has this general form:


<syntaxhighlight lang="text">
<pre>
(freq_start - freq_end @ max_channel_width), (max_power), optional_flags
(frequency_start - frequency_end @ maximum_channel_width), (maximum_power), optional_flags
</syntaxhighlight>
</pre>


Example:
Example:


<syntaxhighlight lang="text">
<pre>
(5250 - 5350 @ 80), (24), DFS, AUTO-BW
(5250 - 5350 @ 80), (24), DFS, AUTO-BW
</syntaxhighlight>
</pre>


{| class="wikitable"
In that example:
! Item
! Meaning


| ! Effect on final wireless behavior                                                                                                              |
* <code>5250 - 5350</code> is the allowed frequency range in MHz.
| ------------------------------------------------------------------------------------------------------------------------------------------------ |
* <code>@ 80</code> means the maximum allowed channel width is 80 MHz.
| <code>@ 80</code>, <code>@ 160</code>, <code>@ 320</code>                                                                                        |
* <code>(24)</code> means the maximum transmit power is 24 dBm.
| Maximum channel width allowed by that regulatory rule, in MHz.                                                                                  |
* <code>DFS</code> means Dynamic Frequency Selection is required.
| Can limit whether 20/40/80/160/320 MHz operation is accepted.                                                                                   |
* <code>AUTO-BW</code> affects how the regulatory code handles bandwidth across adjacent ranges.
| -                                                                                                                                                |
| <code>(24)</code>                                                                                                                               |
| Maximum transmit power in dBm.                                                                                                                  |
| Caps the transmit power exposed to the driver, <code>iw</code>, and hostapd.                                                                    |
| -                                                                                                                                                |
| <code>(4000 mW)</code>                                                                                                                          |
| Maximum transmit power in milliwatts.                                                                                                            |
| Same function as a dBm value, only expressed in milliwatts.                                                                                     |
| -                                                                                                                                                |
| <code>DFS</code>                                                                                                                                 |
| Dynamic Frequency Selection required. The radio must check for radar before using the channel as an access point.                                |
| Can delay AP startup because Channel Availability Check / radar scanning must complete before normal operation.                                  |
| -                                                                                                                                                |
| <code>AUTO-BW</code>                                                                                                                             |
| Automatic regulatory bandwidth handling. Allows the regulatory code to evaluate bandwidth across compatible adjacent regulatory ranges.         |
| Can affect whether a requested wide channel is accepted. It does not mean automatic channel selection.                                          |
| -                                                                                                                                                |
| <code>NO-OUTDOOR</code>                                                                                                                          |
| Outdoor operation is not allowed under that rule.                                                                                                |
| Restricts legal use. Enforcement depends on the driver/regulatory stack; the device cannot physically determine indoor versus outdoor placement. |
| -                                                                                                                                                |
| <code>NO-IR</code>                                                                                                                              |
| No Initiating Radiation. The device may not initiate transmissions on that range.                                                                |
| Usually prevents AP/master mode and active scanning on that range.                                                                              |
| -                                                                                                                                                |
| <code>NO-OFDM</code>                                                                                                                            |
| Orthogonal Frequency-Division Multiplexing is not allowed.                                                                                      |
| Restricts use of OFDM-based modes. Mostly relevant to special cases such as old 2.4 GHz channel 14 behavior.                                    |
| -                                                                                                                                                |
| <code>wmmrule=ETSI</code>                                                                                                                        |
| Applies ETSI Wireless Multimedia / Quality of Service contention parameters.                                                                    |
| Affects Wireless Multimedia behavior, not DFS startup timing.                                                                                    |
| }                                                                                                                                                |


=== Practical Interpretation ===
=== Flag Meanings ===


The regulatory database affects the final usable wireless settings through this path:
<code>DFS</code> means Dynamic Frequency Selection. The radio must check for radar before using that channel as an access point. This can delay wireless startup.


<syntaxhighlight lang="text">
<code>AUTO-BW</code> means automatic bandwidth handling inside the regulatory code. It helps determine whether wider channels are allowed across compatible frequency ranges. It does not mean automatic channel selection.
regulatory.db
↓
kernel cfg80211 regulatory rules
↓
iw reg get / iw phy
↓
hostapd channel validation
↓
radio starts, waits for DFS, falls back, or fails
</syntaxhighlight>


For boot-time testing, the most important flags are:
<code>NO-OUTDOOR</code> means outdoor use is not allowed for that frequency range.


<syntaxhighlight lang="text">
<code>NO-IR</code> means No Initiating Radiation. The device is not allowed to initiate transmissions on that range. In practice, this can prevent access point mode or active scanning.
DFS
NO-IR
AUTO-BW
</syntaxhighlight>


The <code>DFS</code> flag is the primary item associated with radar scanning and delayed AP availability. Removing or changing power alone is not a direct test of DFS behavior. A direct test compares the same frequency range with and without the <code>DFS</code> flag.
<code>NO-OFDM</code> means Orthogonal Frequency-Division Multiplexing is not allowed. This is mostly relevant to special legacy restrictions.


=== United States Regulatory Insert ===
<code>wmmrule=ETSI</code> applies ETSI Wireless Multimedia parameters. This affects Quality of Service / contention behavior, not DFS startup delay.


<syntaxhighlight lang="text">
=== Practical Effect ===
 
These flags do affect final wireless behavior. They can determine whether OpenWRT, the kernel, the wireless driver, and hostapd allow a radio to start on a given channel.
 
For DFS startup testing, the important item is the <code>DFS</code> flag. If the same frequency range starts faster after removing <code>DFS</code>, then DFS/radar handling was part of the delay.
 
Changing transmit power alone is not a direct DFS test.
 
=== US Regulatory Block ===
 
<pre>
country US: DFS-FCC
country US: DFS-FCC
# S1G Channel 1-3
# S1G Channel 1-3
Line 114: Line 75:
# channels 1-6 EIRP=40dBm(43dBm peak)
# channels 1-6 EIRP=40dBm(43dBm peak)
(57240 - 71000 @ 2160), (40)
(57240 - 71000 @ 2160), (40)
</syntaxhighlight>
</pre>
 
=== Notes ===
 
* Channel 116 is inside the normal 5 GHz DFS block.
* If DFS is removed from the applicable range and AP startup becomes faster, that supports DFS/radar handling as a startup-delay factor.
* A channel selected by automatic channel selection should not be assumed to be the objectively least congested channel. It only means the channel was selected by the available scan/survey data and the active regulatory/driver/hostapd rules.
* A scan table showing fewer visible APs on a channel supports that the channel is cleaner from a visible Wi-Fi Basic Service Set perspective, but does not prove lowest total RF noise or lowest airtime utilization.

Revision as of 01:43, 29 June 2026

OpenWRT Wireless Regulatory Flags

OpenWRT uses the Linux wireless regulatory database to decide which channels, channel widths, and transmit powers are allowed for a selected country code.

A regulatory rule has this general form: 

(frequency_start - frequency_end @ maximum_channel_width), (maximum_power), optional_flags

Example: 

(5250 - 5350 @ 80), (24), DFS, AUTO-BW

In that example:

  • 5250 - 5350 is the allowed frequency range in MHz.
  • @ 80 means the maximum allowed channel width is 80 MHz.
  • (24) means the maximum transmit power is 24 dBm.
  • DFS means Dynamic Frequency Selection is required.
  • AUTO-BW affects how the regulatory code handles bandwidth across adjacent ranges.

Flag Meanings

DFS means Dynamic Frequency Selection. The radio must check for radar before using that channel as an access point. This can delay wireless startup.

AUTO-BW means automatic bandwidth handling inside the regulatory code. It helps determine whether wider channels are allowed across compatible frequency ranges. It does not mean automatic channel selection.

NO-OUTDOOR means outdoor use is not allowed for that frequency range.

NO-IR means No Initiating Radiation. The device is not allowed to initiate transmissions on that range. In practice, this can prevent access point mode or active scanning.

NO-OFDM means Orthogonal Frequency-Division Multiplexing is not allowed. This is mostly relevant to special legacy restrictions.

wmmrule=ETSI applies ETSI Wireless Multimedia parameters. This affects Quality of Service / contention behavior, not DFS startup delay.

Practical Effect

These flags do affect final wireless behavior. They can determine whether OpenWRT, the kernel, the wireless driver, and hostapd allow a radio to start on a given channel.

For DFS startup testing, the important item is the DFS flag. If the same frequency range starts faster after removing DFS, then DFS/radar handling was part of the delay.

Changing transmit power alone is not a direct DFS test.

US Regulatory Block

country US: DFS-FCC
	# S1G Channel 1-3
	(902 - 904 @ 2), (30)
	# S1G Channel 5-35
	(904 - 920 @ 16), (30)
	# S1G Channel 37-51
	(920 - 928 @ 8), (30)
	(2400 - 2472 @ 40), (30)
	# 5.15 ~ 5.25 GHz: 30 dBm for master mode, 23 dBm for clients
	(5150 - 5250 @ 80), (23), AUTO-BW
	(5250 - 5350 @ 80), (24), DFS, AUTO-BW
	# This range ends at 5725 MHz, but channel 144 extends to 5730 MHz.
	# Since 5725 ~ 5730 MHz belongs to the next range which has looser
	# requirements, we can extend the range by 5 MHz to make the kernel
	# happy and be able to use channel 144.
	(5470 - 5730 @ 160), (24), DFS
	(5730 - 5850 @ 80), (31), AUTO-BW
	# https://www.federalregister.gov/documents/2021/05/03/2021-08802/use-of-the-5850-5925-ghz-band
	# max. 33 dBm AP @ 20MHz, 36 dBm AP @ 40Mhz+, 6 dB less for clients
	(5850 - 5895 @ 40), (27), NO-OUTDOOR, AUTO-BW, NO-IR
	# 6g band
	# https://www.federalregister.gov/documents/2020/05/26/2020-11236/unlicensed-use-of-the-6ghz-band
	(5925 - 7125 @ 320), (12), NO-OUTDOOR, NO-IR
	# 60g band
	# reference: section IV-D https://docs.fcc.gov/public/attachments/FCC-16-89A1.pdf
	# channels 1-6 EIRP=40dBm(43dBm peak)
	(57240 - 71000 @ 2160), (40)
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