802.11 Standards and Features

What it is

The 802.11 family of standards defines how Wi-Fi devices talk to each other.

Each new amendment raised the speed and added features, and most kept compatibility with the older ones. A device and an access point can use a standard only if both support it.

Learning the list is mostly learning which band each standard uses and what it added.

How it works

Each amendment changed the radio method, and the later ones added channel width, streams and efficiency.

The main standards

The rates are theoretical limits for the best case. Real throughput is lower, because of overhead and conditions on the link.

Marketing names

The Wi-Fi Alliance gives simple generation names. 802.11n is Wi-Fi 4, 802.11ac is Wi-Fi 5 and 802.11ax is Wi-Fi 6. Earlier standards did not get a number name in the same way.

Features that arrived with n and ac

Several features helped the newer standards reach higher speeds.

• Channel bonding joins channels to make a wider one, such as 40 MHz in n and 80 or 160 MHz in ac.
• MIMO uses several antennas and streams at once. The MIMO page covers it.
• Frame aggregation combines several frames into one transmission to cut overhead.
• Block acknowledgement lets one reply confirm a group of frames.
• Short guard interval shortens the gap between symbols for a higher rate when conditions are good.

Other amendments to know

Some amendments add a function and not a new speed.

Compatibility and mixed networks

When an older client joins, the network must protect the older client from newer transmissions. This extra protection costs airtime.

An old 802.11b client on a 2.4 GHz network slows everyone, because it transmits slowly and the network needs protection mechanisms. Removing the lowest data rates reduces this effect.

Band settings in RouterOS

On the legacy wireless package the band setting selects the standards that the radio uses.

/interface wireless set wlan1 band=2ghz-b/g/n
/interface wireless set wlan1 band=5ghz-a/n/ac

• 2ghz-b/g/n allows b, g and n clients on 2.4 GHz.
• 5ghz-a/n/ac allows a, n and ac clients on 5 GHz.
• A narrower band setting such as 2ghz-onlyn removes support for the oldest clients.

On the wifi driver of RouterOS v7, the band names include the ax standard, for example 5ghz-ax. Only hardware that supports the standard can use it.

Scan list (legacy wireless package, RouterOS v6)

The scan-list setting limits the frequencies that an interface tries. A station uses it when it looks for an access point, and an access point with frequency=auto chooses its channel from it.

/interface wireless set wlan1 frequency=auto scan-list=5180,5200,5220
/interface wireless set wlan1 frequency=auto scan-list=5500-5700

• Entries are frequencies in MHz, separated by commas.
• A range uses a hyphen, as in 5500-5700.
• A short list lets a station find its access point faster.
• It also keeps an access point away from channels that you do not want it to use.

Choosing a band

Use 5 GHz for speed and capacity and keep 2.4 GHz for range and older devices.

Reading the standard from a rate

The registration table shows the rate that a client uses. The rate often hints at the standard. A rate above the 54 Mbps limit of a and g shows that the client uses n, ac or ax.