Backup Link Establishment for Low Latency Communication

Achieving low latency communication is crucial when link quality deteriorates. This presentation by Qi Wang et al. from Apple Inc. introduces the concept of establishing a Backup Link to swiftly switch LL communication to a better link, enhancing data transmission efficiency in scenarios where the primary link quality degrades. Various assumptions, procedures for establishing and updating Backup Links, and considerations for LL traffic management are discussed in detail.

• Backup Link
• Low Latency Communication
• Data Transmission
• Link Quality
• Apple Inc.

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1. filename: 11-20-1028-00-Backup Link.pptx Backup Link for Low Latency Communication Date: 2020-07-08 Authors: Name Affiliations Address Phone Email Qi Wang Yong Liu Jinjing Jiang Lochan Verma Jarkko Kneckt Tianyu Wu Sk Yong Guoqing Li Apple Inc. qi_wang2@apple.com Submission Slide 1 Qi Wang et al., Apple Inc.

2. filename: 11-20-1028-00-Backup Link.pptx Overview To achieve low latency (LL), when a link quality deteriorates, it s critical to switch the LL communication to a new and better link quickly. The deteriorated link is no longer suitable for continued data transmission or link quality change notification. In some devices, there is an extra radio that is not used by ongoing LL communication: An extra tx/rx-capable radio An extra rx-only radio (e.g., scan radio) AP - MLD LL Communication Link Backup Link Such an extra radio can be used to establish a Backup Link to reduce latency. STA - MLD Submission Slide 2 Qi Wang et al., Apple Inc.

3. filename: 11-20-1028-00-Backup Link.pptx Assumptions AP-MLD maintains the same or higher number of simultaneous links than STA-MLD. Ex: AP-MLD supports 3 independent links, each in 2.4GHz, 5GHz, and 6GHz STA-MLD supports: Independent 2.4GHz and 5GHz links, or independent 2.4GHz and 6GHz links 5GHz and 6GHz links cannot operate independently STA-MLD may have an extra rx-only radio (e.g. scan radio). AP-MLD 2.4 GHz 5 GHz 6 GHz LL communication is conducted over a Primary Low Latency Link (e.g., the 5GHz link) as a result of either explicit or implicit agreement. Link 2 Ex: primary LL link Link 3 (Virtual Link) Link 1 2.4 GHz 5 or 6 GHz STA-MLD Optionally, rx-only dedicated scan radio Submission Slide 3 Qi Wang et al., Apple Inc.

4. filename: 11-20-1028-00-Backup Link.pptx Backup Link Establishment and Update (1/2) AP-MLD elects a Backup Link that operates independently from the Primary Low Latency Link Ex: 5GHz link as the primary link and 2.4GHz link as the backup link STA-MLD informs AP-MLD: Whether it supports Backup Link Whether its Backup Link is rx-only or tx/rx-capable and other capability information (e.g., supported BWs, PPDU types) Submission Slide 4 Qi Wang, et al., Apple Inc.

5. filename: 11-20-1028-00-Backup Link.pptx Backup Link Establishment and Update (2/2) A backup link agreement may be applicable only to LL traffic Ex: traffic that is associated with certain access categories (e.g, AC_VO) and certain TIDs. After Backup Link establishment, both AP-MLD and STA- MLD commit to be available on Backup Link during the LL communication on Primary LL link. AP-MLD may update the Backup Link due to various reasons, for examples: Current Backup Link becomes unavailable Ex: Backup Link becomes the new LL communication link STA s change in Backup Link preference Other considerations. Submission Slide 5 Qi Wang, et al., Apple Inc.

6. filename: 11-20-1028-00-Backup Link.pptx Backup Link Enabling Radio Case 2: Backup link enabling radio that is rx-only (e.g., a scan radio) Case 1: Backup link enabling radio is tx/rx-capable: A Scan Radio typically is a rx-only simple radio which scans through each channel, listens for per channel dwell time , and obtains statistics indicating the corresponding channel quality, and repeats such operation every Scan Interval. Example: a regular tx/rx-capable radio that is not used by the Primary LL Link, e.g., the 2.4GHz link where the 5GHz link is the Primary LL Link. Submission Slide 6 Qi Wang, et al., Apple Inc.

7. filename: 11-20-1028-00-Backup Link.pptx Operation of Backup Link Enabled by Tx/Rx-capable Radio (1/2) When AP-MLD detects link quality deterioration on Primary LL Link: AP-MDL sends a notification frame to STA-MLD on Backup Link, LL communication is switched from Primary LL Link to Backup Link or another link informed by the Notification. STA-MLD s power save schedule on Backup Link ensures it s available to receive DL packet from AP-MLD during the LL packet exchange on Primary LL link Two options of STA-MLD s Backup Link PS schedule are described in the next slide. Submission Slide 7 Qi Wang, et al., Apple Inc.

8. filename: 11-20-1028-00-Backup Link.pptx Operation of Backup Link Enabled by Tx/Rx-capable Radio (2/2) Option 1: STA-MLD s Backup Link PS schedule aligns with the LL traffic schedule on Primary LL Link Option 2: STA-MLD s Backup Link PS schedule aligns with the PS schedule on Primary LL Link Doze Awake Awake Time Time LL traffic periodic interval (e.g., 16.7/13.9/11.1/8.3ms) Power save schedule of Primary LL Link LL traffic schedule on Primary LL link Doze Awake Awake Doze Awake Awake Time Time Power save schedule of Backup Link. -- Option 2 Power save schedule of Backup Link Option 1 Submission Slide 8 Qi Wang, et al., Apple Inc.

9. filename: 11-20-1028-00-Backup Link.pptx Operation of Backup Link Enabled by Rx- only Radio (1/2) When AP-MLD detects link quality deterioration on Primary LL Link: AP-MDL sends a notification frame to STA-MLD on Backup Link, LL communication is switched from Primary LL Link to the Link informed by the Notification. STA-MLD is available to receive DL packet from AP- MLD on Backup Link during the LL packet exchange on Primary LL link. For example, for a scan radio enabled backup link: Two options of Scan radio s scanning schedule are described in the next slide. Submission Slide 9 Qi Wang, et al., Apple Inc.

10. filename: 11-20-1028-00-Backup Link.pptx Operation of Backup Link Enabled by Rx- only Radio (Ex: scan radio) (2/2) Option 1: Scan radio s non-scanning phase (i.e., dwell phase) aligns with the schedule of LL traffic on Primary LL Link Time LL traffic periodic interval (e.g., 16.7/13.9/11.1/8.3ms) LL traffic schedule on Primary LL link Scan interval Dwell phase (Scan radio parks at Backup link) Scan phase (Scan radio scans through channels) Time Scan radio s Schedule Option 1 Doze Option 2: Scan radio s non-scanning phase (i.e., dwell phase) aligns with the PS schedule on Primary LL Link Awake Time Power save schedule on Primary LL link Scan interval Dwell phase (Scan radio parks at Backup link) Scan phase (Scan radio scans through channels) Time Scan radio s Schedule Option 2 Submission Slide 10 Qi Wang, et al., Apple Inc.

11. filename: 11-20-1028-00-Backup Link.pptx Summary We have proposed the establishment and operation of a Backup Link to assist low latency communication. The usage of Backup Link reduces the latency of communication. Submission Slide 11 Qi Wang, et al., Apple Inc.

12. filename: 11-20-1028-00-Backup Link.pptx Straw Poll Do you support to define a backup link to assist the low latency communication ? Result: Y/N/Abs Submission Slide 12 Qi Wang, et al., Apple Inc.