There’s a substantial amount of discuss across the functionality of Wi-Fi 7 (IEEE 802.11be) to revolutionize the wi-fi expertise. It’s not hype. A key characteristic that delivers this transformative affect is multi-link operation (MLO). A compulsory and defining part of 802.11be, MLO permits a multi-link machine (MLD) to concurrently function throughout a number of frequency bands, together with 2.4 GHz, 5 GHz, and 6 GHz.
Entry level (AP) and non-AP MLDs study one another’s MLO parameters and capabilities by means of the multi-link data components exchanged in frames like Beacons and Affiliation Request/Response. On this weblog, I’ll illustrate MLO’s affect on wi-fi connectivity and present you the way it works in simultaneous switch/obtain (STR) mode.
How does multi-link operation (MLO) improve wi-fi connectivity?
MLO introduces vital advantages for quite a lot of use instances. Key enhancements embody:
- Simultaneous use of a number of bands. MLDs can transmit (Tx) and obtain (Rx) knowledge over a couple of band on the similar time. That is helpful in environments with heavy congestion, because it avoids interference on any single band.
- Improved throughput. MLO leverages the mixed capability of a number of channels throughout totally different bands to allow larger combination throughput. This makes Wi-Fi 7 excellent for bandwidth-heavy purposes like video streaming, digital actuality, and on-line gaming.
- Diminished latency. By offloading site visitors throughout a number of channels. That is significantly helpful in gaming, video conferencing, or different apps that require real-time communication.
- Higher reliability and robustness. If one band (for instance, 2.4 GHz) experiences congestion, then station (STA) MLDs can seamlessly change to a much less congested band (corresponding to 6 GHz) with out dropping the connection. That is extraordinarily useful in areas with busy radio frequency (RF) site visitors, corresponding to stadiums, flats, and places of work.
Sort of MLO operation modes
Wi-Fi 7 defines a number of single and multi-radio MLO modes, with stations capable of assist these modes based mostly on their respective {hardware} capabilities. Varied software program thresholds—corresponding to bandwidth necessities, band preferences, RF congestion, and QoS—will affect and information a station’s alternative of working mode.
Amongst these modes, MLSR is required to be supported by all AP and non-AP MLDs. Assist for EMLSR and STR modes is necessary for AP MLDs, however elective for non-AP MLDs (stations). STR is presently included by most distributors, making this mode a wonderful beginning place for dissection.
MLO’s STR mode in motion
In STR operation, every hyperlink can be utilized to Tx or Rx concurrent bodily layer protocol knowledge models (PPDUs) with none synchronization. Determine 2 illustrates an instance the place an AP MLD and a non-AP MLD are working over an STR hyperlink pair. Each units contend for entry to the wi-fi medium and interact in subsequent body exchanges on these hyperlinks.
After the AP MLD and the non-AP MLD full a multi-link setup to efficiently set up hyperlink 1 and hyperlink 2, and with the hyperlinks enabled, AP 2 can obtain knowledge frames from STA 2 on hyperlink 2. In the meantime, AP 1 contends for the wi-fi medium and, upon securing a transmit alternative (TXOP), transmits knowledge frames to STA 1 on hyperlink 1.
Subsequent, let’s conduct a lab take a look at utilizing Cisco’s CW9178I AP operating on Catalyst 9800 Wi-fi LAN controller (WLC) to exhibit STR in motion.
The entry level underneath take a look at (APUT) is configured to function on 2.4 GHz (20 MHz) and 5 GHz (40 MHz) bandwidths with a WPA3-SAE WLAN. In step one of the take a look at, Wi-Fi 7/802.11be/MLO is enabled on each bands. We’re utilizing a Qualcomm 7800-based STR/MLMR-capable station, whereas the CW9178I AP serves because the sniffer—able to capturing knowledge throughout a number of bands and decoding Wi-Fi 7 frames.
Subsequent, let’s affiliate the STAUT and examine the potential particulars in each the WLC and Wireshark. Through the affiliation course of, a number of components are exchanged: the MLO data components for the 5 GHz Affiliation hyperlink, in addition to the “Per-STA Profiles” data components containing particulars concerning the non-association hyperlink (2 GHz).
The WLC identifies the STA as STR succesful if the “Most Variety of Simultaneous Hyperlinks” worth within the ML data component of the affiliation request is non-zero. This means the variety of radios the station is utilizing for its affiliation. See Determine 4 under for the corresponding Wireshark seize.
The Catalyst 9800 WLC supplies a transparent show of the STA’s 802.11be capabilities, together with MLD hyperlinks with Slot IDs and bands, MLO mode assist (STR/eMLSR), and Tx/Rx RF and knowledge statistics for every band. Equal CLI instructions are additionally obtainable, although not coated on this weblog.
Now that the STA has related on the 5G band with an STR hyperlink to each the 5G and 2G bands, let’s provoke site visitors for one minute to confirm STR operation. Utilizing the IxChariot server, we are going to start full-bandwidth Downlink UDP site visitors. Initially, site visitors will movement solely on the 5G band, as it’s the solely lively affiliation hyperlink. Nonetheless, the STA will quickly assess the necessity for a secondary hyperlink to realize larger bandwidth. It should then ship a QoS Null knowledge body over the secondary (2G) hyperlink. The AP acknowledges this request and permits simultaneous knowledge transmission throughout each bands.
Determine 6 reveals the sequence beginning with knowledge on channel 36, adopted by a QoS Null knowledge body on channel 6, and concluding with simultaneous knowledge transmission on each channel 6 and channel 36.
The Catalyst 9800 WLC affords a complete view of the consumer’s efficiency on every MLO hyperlink, with displays offering detailed Tx/Rx knowledge together with RF statistics.
Following the one-minute site visitors run, the common throughput measured is 747 Mbps, as proven in Determine 8.
To offer a comparability, the take a look at was repeated underneath the identical situations, however with 802.11be/MLO disabled, operating in 802.11ax mode as a substitute. The typical throughput was 506 Mbps.
The desk under summarizes the throughput comparability between shoppers. The affect is certainly transformative: Wi-Fi 7 with STR MLO considerably outperforms Wi-Fi 6, delivering a 47% throughput improve, together with extra environment friendly spectrum utilization.
The CW9178I, CW9176I, and CW9176D1 APs, together with 9800 sequence wi-fi controllers, will absolutely assist Wi-Fi 7 capabilities and options from IOS XE 17.15.2 onward.
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