There’s an excessive 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 impression is multi-link operation (MLO). A compulsory and defining part of 802.11be, MLO allows a multi-link gadget (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 the multi-link data parts exchanged in frames like Beacons and Affiliation Request/Response. On this weblog, I’ll illustrate MLO’s impression 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 circumstances. Key enhancements embody:
- Simultaneous use of a number of bands. MLDs can transmit (Tx) and obtain (Rx) knowledge over multiple 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 completely different bands to allow larger combination throughput. This makes Wi-Fi 7 excellent for bandwidth-heavy functions 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 (reminiscent of 6 GHz) with out dropping the connection. That is extraordinarily useful in areas with busy radio frequency (RF) site visitors, reminiscent of stadiums, residences, and workplaces.
Sort of MLO operation modes
Wi-Fi 7 defines a number of single and multi-radio MLO modes, with stations in a position to assist these modes primarily based on their respective {hardware} capabilities. Varied software program thresholds—reminiscent of 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. Help for EMLSR and STR modes is obligatory for AP MLDs, however elective for non-AP MLDs (stations). STR is at present 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 items (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 gadgets contend for entry to the wi-fi medium and have interaction 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 CW9178 AP working on Catalyst 9800 Wi-fi LAN controller (WLC) to display STR in motion.
The entry level below 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 CW9178 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 verify the aptitude particulars in each the WLC and Wireshark. In the course of the affiliation course of, a number of parts are exchanged: the MLO data parts for the 5 GHz Affiliation hyperlink, in addition to the “Per-STA Profiles” data parts 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 beneath for the corresponding Wireshark seize.
The Catalyst 9800 WLC gives 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 accessible, 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 energetic affiliation hyperlink. Nevertheless, the STA will quickly assess the necessity for a secondary hyperlink to attain larger bandwidth. It can then ship a QoS Null knowledge body over the secondary (2G) hyperlink. The AP acknowledges this request and allows 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 presents 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 typical throughput measured is 747 Mbps, as proven in Determine 8.
To offer a comparability, the take a look at was repeated below the identical situations, however with 802.11be/MLO disabled, working in 802.11ax mode as an alternative. The common throughput was 506 Mbps.
The desk beneath summarizes the throughput comparability between shoppers. The impression 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 CW9178, CW9176I, and CW9176D APs, together with 9800 sequence wi-fi controllers, will absolutely assist Wi-Fi 7 capabilities and options within the upcoming IOS XE 17.15.2 (at present in Beta) launch.
The CW9178, CW9176I, and CW9176D APs, together with 9800 sequence wi-fi controllers, will absolutely assist Wi-Fi 7 capabilities and options within the upcoming IOS XE 17.15.2 (at present in Beta) launch.
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