What is a regulatory domain?
Wi-Fi uses unlicensed radio spectrum, but unlicensed does not mean unregulated. Each country decides which frequencies Wi-Fi may use, how much power a transmitter may put out, and what extra rules apply on shared channels. A regulatory domain packages those rules. Access points, routers and client adapters apply them based on a country code, and enterprise vendors often name domains after the regulator, such as FCC for the United States and ETSI for Europe.
What the regulatory domain controls
- Allowed channels: which channels appear in the router's channel list.
- Maximum transmit power: limits per band and sometimes per channel.
- Radar avoidance: whether Dynamic Frequency Selection (DFS) is required on certain 5 GHz channels.
- Indoor or outdoor use: some regions allow certain channels indoors only.
Differences that show up in practice
| Band | Regulatory differences |
|---|---|
| 2.4 GHz | Wi-Fi equipment for the United States uses channels 1 to 11; much of Europe and many other countries allow 1 to 13; channel 14 is limited to Japan and 802.11b. |
| 5 GHz | In the United States, channels 52 to 64 and 100 to 144 require DFS; Europe has similar DFS rules on its middle 5 GHz channels. Before using a DFS channel, an AP must listen for radar (typically 60 seconds), and it must leave the channel if it detects radar. |
| 6 GHz | The United States opened 5.925 to 7.125 GHz (1,200 MHz) to Wi-Fi; Europe opened only the lower part of the band. Other countries differ again. |
How devices learn the domain
On an access point or router, the administrator selects the country, or the vendor fixes it for the market where the device is sold. Client devices can read the country information that APs advertise in their beacons (an 802.11d feature) and adjust to it. On DFS channels, clients scan passively, waiting to hear an AP's beacon before they transmit.
Troubleshooting cues
- A laptop bought in the United States cannot see a network that works for other devices: the AP may be on channel 12 or 13, which many US clients will not use. Move the AP to 1, 6 or 11.
- An AP set to the wrong country may use channels or power levels that are illegal where it is installed. Set the country to the actual location; changing it to unlock extra channels breaks local regulations.
- 5 GHz clients drop for a moment and the AP's channel changes on its own: the AP likely detected radar on a DFS channel and moved. Non-DFS channels (36 to 48 or 149 to 165 in the United States) avoid this.
- A newly powered-on AP takes about a minute before its 5 GHz network appears: it is running the radar check on a DFS channel.
- A Wi-Fi analyzer shows networks on channels your own equipment does not offer: those devices are set to, or were sold for, a different domain.
Regulatory domain on the CompTIA A+ exam
Core 1 objective 2.2 lists regulations as a bullet under wireless channels, next to channel selection. Know that the legal channel list and power limits depend on the country, that the United States uses 2.4 GHz channels 1 to 11, and that some 5 GHz channels require DFS to avoid interfering with radar. If a question describes a device that cannot use a channel that works elsewhere, or asks why a router's channel list differs by country, think regulatory domain.