if we use SSID Discovery in 6GHz traditional ways as in 2.4GHz or 5GHz, that is scanning every channel in 6GHz which will cause huge performance problems.
6GHz has 59 Channels (assuming country uses full spectrum of 1200MHz like US and most countries are considering following US) scanning every channel to identify the SSID will take approximately 6 to 8 Seconds minimum.
6GHz devices are broadly classified in 3 Categories
1) Low Power Indoor (LPI) - Wireless devices both Access points & User devices used indoors.
2) Standard Power - Wireless Devices both Access points & user devices can be used both Indoor & outdoors. Devices must operate under the control of an AFC (Automatic Frequency Coordination) system and system dynamically manages the frequencies and power levels to prevent interference with incumbent services in the 6 GHz band.
You can find the countries using and Considering AFC usage in below URL as Wi-Fi alliance website.
3) Very Lower Power Devices - These devices are designed for short-range and high data-rate applications and can be used both Indoor & outdoor without the control of AFC.
Based on the above different clauses of the devices
1) 6ID - Low Power Indoor Access Point
2) 6PP - Lower Power Indoor Subordinate device like a repeater or extender to extend the wireless signal.
3) 6XD - Low Power Indoor Client. Example NIC like Intel AX211, AX201 etc.
4) 6CD - Dual mode Client Indoor & outdoor Client. Client devices can be connected to and controlled either by Lower Indoor Access point / Standard power access point.
Most client devices manufactured in May 2024 or after are 6CD.
5) 6SD - Standard power Access point and these devices managed by AFC / Automatic Frequency Coordination system to avoid interference with incumbent services.
6) 6FX - Devices under the control Standard power Access point.
7) 6FC - Fixed Client and associated & controlled by Standard access point. That is this device Permanently Mounted at location like a wireless Camera etc.
Lower power Indoor Access point operate in 5.925-7.125 GHz (1200 MHz as reference in United states) and Standard power Access point operate 5.925-6.425 GHz and 6.525-6.875 GHz and managed by Automatic Frequency Coordinate system.
Why we need know to all these in 6GHz discovery of SSID?
Due to the above, we may see a Laptop with Intel AX211/AX411 / MacBook Pro (M2-chip)/Samsung Galaxy Tab S8 etc. able to connect to Access point Indoor in 6GHz but unable to roam or connect to outdoor Access point (controlled by AFC) in 6GHz.
Note: Automatic frequency control can vary based on the country due to different regulatory requirements and spectrum allocations, but most countries follow US.
For example: I googled FCCID of Samsung S23 Ultra found it as A3LSMS918B and went to https://fccid.io and searched using FCCID and found below information.
(Search for attestation letter once you search results using FCCID)
Note: FCCID normally found when you buy the device on its package
Discovery of the SSID in 6GHz is categorized broadly into ways
1.Out of Band Discovery
Wi-Fi6E mandates the access points supporting multiple radios (2.4GHz, 5GHZ & 6GHz) should advertise 6GHz SSID information in other bands.
This helps the user devices scanning on 2.4 GHz or 5GHz will know about 6GHz SSID and also improves the performance of the wireless. As we know 6GHz has 59 Channels (using complete 1200 MHz frequency), if user device needs to scan all the 59 channels to know the details of SSID, it will take a lot of time in just discovering the SSID only and already we have proven methods which are already working in 2.4GHz & 5GHz.
Discovery of 6GHz SSID one way using Reduced Neighbor Report (RNR) and more commonly used by all the devices supporting 6GHz radio.
If AP is supporting all the 3 radios and broadcasting SSID, you will see Reduced Neighbor Report (RNR) information element in the Beacon & Probe response.
Two Neighbor AP Information sub-elements are seen where one Neighbor AP information contains information about 6GHz Channel, Short SSID and BSSID information of all the SSIDs broadcasted by access point.
Each TBTT information sub-element will have short SSID and BSSID associated to the SSID.
Please note Neighbor AP /Co-located AP in this context means Each radio in the access point. As we have 3 radios in the access point, radio (2.4GHz) has two Neighbor /Co-located APs that is 5GHz radio & 6GHz radios on the same access point and vice-versa.
Below are details of TBTT Information Sub-element BSS parameters nothing but more details about the SSID.
Same SSID - True what it means let me try to explain with example.
Assume we captured Beacon information for SSID say "TEST-SSID" on 5GHz radio. Same SSID - True says that Short SSID & BSSID details we are looking at specific TBTT information are for the Same SSID TEST-SSID for 6GHz radio.
Multiple BSSID - Before 6GHz / Wi-Fi 6E, one beacon will have information about one BSSID associated to radio like 2.4GHz /5 GHz regards to SSID. When an AP supports multiple SSIDs, it typically sends out separate beacon frames for each SSID. This can lead to beacon overhead, where a significant portion of the available airtime is consumed by these beacon frames. For example, if access point with dual radio is broadcasting 2 SSIDs, we will have 4 Beacons sent out by the access point. Two Beacons for 2.4GHz radio and two Beacons for 5GHz radio. Each Beacon will have separate BSSID per radio per SSID.
Name of SSID | BSSID 2.4GHz | BSSID 5GHz | |
1 | SSID-ONE | 00:00:00:00:00:01 | 00:00:00:00:00:02 |
2 | SSID-TW0 | 00:00:00:00:00:03 | 00:00:00:00:00:04 |
Access point will broadcast with WLAN Source address of each BSSID one beacon every 102.4 milliseconds (approximately every 100 milliseconds).
The Multiple BSSID information element allows an AP to consolidate information from multiple SSIDs (per radio) into a single beacon frame. By doing so, it reduces the beacon overhead, significantly reducing the airtime used for beacons.
You can see the Multiple SSIDs in a single beacon. If AP supports Multiple SSIDs advertisement in a single beacon per radio, you will see Information element "Multiple BSSID" where you have all SSIDs relevant information.
Coming back to Multiple BSSID - True in BSS parameters mean 6GHz AP/ radio is part of multiple BSSID set.
PSD Subfield parameter says about the access point using the Low Power Indoor or Standard power or Very Low Power.
OCT Recommended - On channel Tunneling - True means User device can communicate to AP 6GHz radio using other radio like sending management Probe to AP using 2.4 GHz or 5GHz intended 6GHz BSSID or radio of the access point.
Using Reduced Neighbor Report User device will send a Unicast probe request to access point as user device will learn BSSID from beacons broadcasted by access point in 2.4 or 5GHz and helps to avoid broadcast Probe request in 6GHz.
To Conclude using Reduced Neighbor Report information element we can discover the 6GHz SSID of the access point using beacons broadcasted by the access point on 2.4GHz or 5GHz radio.
2. IN Band Discovery
when customers are using only 6GHz on the access point, scanning all the 59 Channels does not sound reasonable. I would not recommend having access points only using 6GHz as user device can easily discover the SSID using Reduced Neighbor Report.
To optimize the performance and avoid delay causing by scanning all the 59 channels in 6GHz, Preferred scanning channel method is used. Preferred scanning channel uses 15 channels, and each channel is 20 MHz
Below is the list of channels used by Preferred Scanning channels (15 in total)
5, 21, 37, 53, 69, 85, 101, 117, 133, 149, 165, 181, 197, 213, and 229 used discover SSID and exchange management frames between user device and access point.
All the 59 channels in 6GHz,
1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 97 101 105 109 113 117 121 125 129 133 137 141 145 149 153 157 161 165 169 173 177 181 185 189 193 197 201 205 209 213 217 221 225 229 233
Using Preferred scanning Channels helps to discover SSID and reduces broadcast Probe request scanning all 59 Channels and optimize the usage of Airtime.
To Conclude Preferred Scanning Channels (PSCs) and Reduced Neighbor Report (RNR) will help in expediting discovery of SSID on 6GHz, reducing broadcast Probe requests and optimizing Airtime usage.
Note: In 6GHz or Wi-Fi 6E, Probe response is broadcast and 6GHz user devices cannot send the probe request once they learn about BSSID to reduce interference and efficient use of spectrum. User device will wait for a random time before sending unicast probe request.
Two more methods are in 6GHz to discover SSID, 1) Unsolicited Probe response - in 6GHz, Probe response is sent by the access point every 20 milliseconds. As we know Probe response is broadcast in 6GHz this will help user devices to avoid sending broadcast Probe request to use airtime efficiently.
2) Fast Initial Link Setup - is commonly knowns as FILS used to discover 6GHz SSID and also reduce broadcast probe request.
Size of FILS is also very less compared to Beacon as it will Short SSID and Channel etc. This Frame is Management Action Broadcast Frame sent every 20 milliseconds.
FILS is normally used in Public Hotspots, Airports or Dense deployments,
In 6GHz NULL probe request are not allowed to avoid broadcast Probe Request and efficiently use Airtime.
To Conclude the article RNR, PSC, Unsolicited Probe response and FILS are the ways discover 6GHz. Most or I would say all the access point will support RNR for sure.
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