Understanding Multi-Link Operation (MLO) in Wi-Fi Networks

What is Multi-Link Operation (MLO)? 

With the introduction of the IEEE 802.11be standard (Wi-Fi 7), Multi-Link Operation (MLO) represents one of the most significant advancements in the modern Wi-Fi technology . MLO as the name signifies, allows devices to establish multiple concurrent links across different frequency bands (2.4GHz, 5GHz, and 6GHz), enabling more efficient use of available RF spectrum and significantly improving throughput, latency, and reliability.

How to identifying MLO Support in a Beacon?

The screenshots below shows the MLO support and capabilities in Beacon of a RUCKUS R770 AP . Let's examine the key indicators:

MLO Capability Indicators

In the first screenshot, we can see several critical fields that indicate MLO support:

  1. Multi-Link Control section shows basic control information with the 802.11be D3.0 tag
  2. EML Capabilities Present: True - Enhanced Multi-Link capabilities are supported
  3. MLD Capabilities Present: True - Multi-Link Device capabilities are available
  4. MLD MAC Address is displayed as "RuckusWirele_c0:a4:bd (cc:1b:5a:c0:a4:bd)". The AP uses the MLD MAC address to route traffic across different radios, ensuring seamless transitions between links. 
  5. Link ID: 0x2 - Specific link identifier within the multi-link setup

The EML (Enhanced Multi-Link) Capabilities section further reveals:

  • EMLSR Support: True (Enhanced Multi-Link Single Radio)

In the MLD Capabilities section, we can see:

  • TID-To-Link Mapping Negotiation Support: 1 TID-to-link mapping allows the devices to assign specific TIDs (voice, video, or data) to specific links. 


Verifying MLO support on a Station :

I have included and example of RUCKUS R770 AP and Pixel-8 connected as MLO Station using 5 GHz and  6 GHz Radios simultaneously:

Below is the CLI output of the  RUCKUS R770 AP representing the Station (Pixel-8) MLO statistics: 

STA MLO Info for 5GHz Radio

  • Station's MAC Address: ca:b1:5b:2b:b0:f8 
  • Operating band : Shows the 5GHz Radio used by the Station.
  • MLO: Yes This means the client is operating in Multi-Link Mode.
  • MLD Addr: ca:b1:5b:2b:b0:f6 This is the Multi-Link Device (MLD) Address. Station will use this MLD MAC address to route traffic across different radios.
  • Num Partner links: 1 → The client has one partner link, meaning it's using two links in total.
  • Max STA Phymode: IEEE80211_MODE_11BEA_EHT40 → The client is using Wi-Fi 7 (802.11be) in 40 MHz bandwidth.
  • EMLSR capable: Yes → The client supports Enhanced Multi-Link Single Radio (EMLSR), allowing efficient multi-link operation even with a single radio.
  • EMLMR capable: No → The client does not support Enhanced Multi-Link Multi-Radio (EMLMR), meaning it may not have multiple independent radios for simultaneous multi-band operation.
  • STR capable: No → Simultaneous Transmit and Receive (STR) is not supported, meaning it may not be using both links for parallel uplink/downlink transmissions.

  • Partner link 0:
    • ADDR: ca:b1:5b:2b:b0:f7 → This is the MAC address of the partner link.(6 GHz Radio of the same Station).
    • Link ID: 2 → Identifier for the link.

STA MLO Info for 6GHz Radio

  • Station's MAC Address: ca:b1:5b:2b:b0:f7 
  • Operating band : Shows the second radio i.e 6GHz Radio used by the Station.
  • MLO: Yes This means the client is operating in Multi-Link Mode.
  • MLD Addr: ca:b1:5b:2b:b0:f6 This is the Multi-Link Device (MLD) Address. Station will use this MLD MAC address to route traffic across different radios. Note the MLD Addr are same for both Radio's. 
  • Num Partner links: 1 → The client has one partner link, meaning it's using two links in total.
  • Max STA Phymode: IEEE80211_MODE_11BEA_EHT160 (Wi-Fi 7, using 160 MHz channel width)
  • EMLSR capable: Yes → The client supports Enhanced Multi-Link Single Radio (EMLSR), allowing efficient multi-link operation even with a single radio.
  • EMLMR capable: No → The client does not support Enhanced Multi-Link Multi-Radio (EMLMR), meaning it may not have multiple independent radios for simultaneous multi-band operation.
  • STR capable: No → Simultaneous Transmit and Receive (STR) is not supported, meaning it may not be using both links for parallel uplink/downlink transmissions.

    • Partner link 0:
      • ADDR: ca:b1:5b:2b:b0:f8 → This is the MAC address of the partner link (5GHz Radio of the same Station).
      • Link ID: 1 → Identifier for the link.

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