6GHz Basics – Scanning and Probing in the 6 GHz band

Passive Scanning – With 1200 MHz to cover and 59 channels to scan, a station with a dwell time of 100 ms per channel would require almost 6 seconds to complete a passive scan of the entire band. This excessive latency would result in slow roaming or even loss of connectivity for the end user and excessive power consumption for the device. New mechanisms are being put in place for mitigation.

Out-of-band discovery – Dual-band or tri-band APs operating in the 6 GHz band and in a lower band (2.4 GHz or 5 GHz) will be discoverable by scanning the lower bands. In the lower band, APs will include information about the 6 GHz BSS via a reduced neighbor report in beacons and probe response frames. The station will therefore have enough information to determine where and how it can associate with the 6 GHz AP.

2.4 GHz Beacon

What are the target beacon transmission times (TBTT)?

As per the 802.11-2020 standards Section Beacon Interval field.

The Beacon Interval field represents the number of time units (TUs) between target beacon transmission times (TBTTs). The period between two TBTTs is referred to as the beacon interval.

The image above has three TBTT sections. Let’s take a look at each section to “try” to understand what’s happening.

TBTT Section # 1

It appears that the BSSID displayed in TTBT #1 is from the 6GHz radio.

TBTT Section # 2

TBTT Section # 3

The 5GHz Beacon will be identical to the 2.4GHz Beacon

The AP will continue to broadcast one Beacon per SSID

2.4/5GHz Synopsis

It appears that the TBTT was incremented by one for each section. The base 6GHz BSSID = d0:4d:c6:ab:3f:40 > enable enable sap 6GHz/101/20MHz/HE.

The RSN IE will display multiple AKMs if the SSID is not “greenfield 6GHz”

What does the 6GHz Beacon contain?

  1. All of the SSIDs are sent in a single Beacon.

Let’s take a look at the Multiple BSSID tag.

Improved Beacon efficiency? In this example, the Beacon carries three SSIDs/BSSIDs. Each Beacon is contained in a “subelement:non-transmitted BSSID Profile.

The WIFI6E BSSID Profile

Profile # 1 – Index 1

Profile # 2 – Index 2

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