Understanding IEEE 802.11 Seamless Roaming Details in August 2023 Presentation
Delve into the intricate call flows illustrating seamless roaming operations in IEEE 802.11, emphasizing context transfer between access points. Explore scenarios like dual links and examine example call flows for a comprehensive understanding.
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August 2023 doc.: IEEE 802.11-23/1884r0 Seamless Roaming Details Date: 2023-11 Authors: Name Affiliations Address Phone email Duncan Ho Qualcomm Technologies 5665 Morehouse Dr., San Diego CA 92121 (858)845-3214 dho@qti.qualcomm.com George Cherian gcherian@qti.qualcomm.com Alfred Asterjadhi aasterja@qti.qualcomm.com Abhishek Patil appatil@qti.qualcomm.com Gaurang Naik gnaik@qti.qualcomm.com Submission Slide 1 Duncan Ho (Qualcomm), et. al.,
August 2023 doc.: IEEE 802.11-23/1884r0 Introduction In this presentation, we discuss a few detailed call flows to show how seamless roaming works All assume no data forwarding but with context transfer between APs (unless otherwise stated) All STA-initiated (can easily be extended to AP- initiated) Submission Slide 2 Duncan Ho (Qualcomm), et. al.,
August 2023 doc.: IEEE 802.11-23/1884r0 Case 1 (dual links) The non-AP MLD is capable of communicating with multiple non-colocated APs during roaming Examples: MLMR non-AP MLDs eMLSR non-AP MLDs and if both the source AP and target AP are operating on the same channel Submission Slide 3 Duncan Ho, Qualcomm Incorporated
August 2023 Example Call Flow doc.: IEEE 802.11-23/1884r0 SMD-MLD AP1 AP2 (target) STA Controller (source) STA UL DL UL/DL data UL/DL data 1. Add Link (AP2:disabled) DL packets may keep coming to AP1 2. STA initiated roaming decision AP1 3. UL: STA drains outstanding MPDUs on AP1 AP1 4. RAI 5. Context transfer from AP1 to AP2 susp end ed 6. Data path switching 8. RAR Enable(AP2) 7. DL data 9. UL/DL data 9. UL/DL data DL packets routed to AP2 10. AP1 drains remaining queued packets 10. DL data from AP1 AP2 11 LinkDisable is sent when last SN on AP1 is flushed/timedout 12. Link Disable(AP1) 13. UL/DL data 13. UL/DL data AP2 RAI: roaming announcement indicator RAR: roaming announcement response Submission Slide 4 Duncan Ho (Qualcomm), et. al.,
August 2023 doc.: IEEE 802.11-23/1884r0 Highlights Assumptions: Source AP, target AP, and the Controller communicate via the backhaul Context can be transferred from source AP to target AP via the backhaul No data forwarding between APs AP1 and AP2 could be generalized to AP MLD1 and AP MLD2 in the call flow STA and non-AP MLD are synonymous in the call flow Context transfer Information about SN (per-TID) Information about PN Non-AP MLD receives DL from BOTH APs staring at step 8 i.e., receiving buffered DL packets from AP1 (to avoid data loss) and fresh packets from AP2 Properties: Lossless Leverage multi-links to deliver DL packets concurrently during roaming Minimizes delays in both UL and DL directions Slide 5 Submission Duncan Ho (Qualcomm), et. al.,
August 2023 doc.: IEEE 802.11-23/1884r0 Case 2 (single link) The non-AP MLD can only communicate with one AP MLD at a time during roaming Examples: MLSR non-AP MLDs eMLSR non-AP MLDs and if the source AP and target AP are operating on different channels Submission Slide 6 Duncan Ho, Qualcomm Incorporated
August 2023 Example Call Flow 2 STA doc.: IEEE 802.11-23/1884r0 SMD-MLD AP1 AP2 (target) STA Controller (source) UL DL UL/DL data UL/DL data 1. Add Link (AP2: disabled) DL packets may keep coming to AP1 AP1 2. STA initiated roaming decision 3. UL: STA drains outstanding MPDUs on AP1 4. RAI AP1 5. Context transfer from AP1 to AP2 susp end ed 6. Data path switch 8. AP1 flushes remaining queued packets 7. DL data DL packets routed to AP2 8. DL data from AP1 9. RAR Link Disable (AP1)/Enable(AP2) 10. UL/DL data 10. UL/DL data AP2 AP2 RAI: roaming announcement indicator RAR: roaming announcement response Submission Slide 7 Duncan Ho (Qualcomm), et. al.,
August 2023 doc.: IEEE 802.11-23/1884r0 Highlights The non-AP MLD communicates with one AP at a time UL resumes at step 9 DL reception from AP1 until step 9, then DL reception only from AP2 Minimal context transfer SN (per-TID) can start at 0 at AP2 PN at AP2 can start at a value higher than the last PN value used at AP1 Properties: Longer UL interruption compared to Case 1 Longer DL interruption compared to Case 1: serialized DL packet delivery prevents parallel DL packet delivery from two APs (lost opportunities) Submission Slide 8 Duncan Ho (Qualcomm), et. al.,
August 2023 doc.: IEEE 802.11-23/1884r0 Case 3 (just jump w/o context transfer) Same as Case 2 except the STA just switches to the target AP immediately after RAI No context transfer performed Submission Slide 9 Duncan Ho (Qualcomm), et. al.,
August 2023 Example Call Flow 3 doc.: IEEE 802.11-23/1884r0 SMD-MLD AP1 AP2 (target) STA STA Controller (source) UL DL UL/DL data UL/DL data 1. Add Link (AP2: disabled) DL packets may keep coming to AP1 AP1 AP1 2. STA initiated roaming decision 3. UL: STA drains outstanding MPDUs on AP1 4. RAI susp end ed susp end ed 5. Data path switching 6. DL data DL packets routed to AP2 7. RAR Link Disable (AP1)/Enable(AP2) AP2 AP2 8. UL/DL data 8. UL/DL data RAI: roaming announcement indicator RAR: roaming announcement response Submission Slide 10 Duncan Ho (Qualcomm), et. al.,
August 2023 doc.: IEEE 802.11-23/1884r0 Highlights The non-AP MLD communicates with one AP at a time UL resumes at step 7 DL receives from AP2 Properties: DL packet loss: buffered DL packets discarded at the source AP However, no context transfer needed Submission Slide 11 Duncan Ho (Qualcomm), et. al.,
August 2023 doc.: IEEE 802.11-23/1884r0 Conclusion In this presentation, we presented a few detailed call flows to show how seamless roaming works without data forwarding between APs As shown in the call flows, the signaling (both over-the-air and between the APs and the Controller) is very similar between the different cases Case 1 (dual-link) offers best performance, followed by Case 2 (single-link), followed by Case 3 (just switch) => We can reuse/extend the 11be ML Reconfig framework and use the same set of management signaling framework to handle all the different cases (i.e., Add link/Link disable and RAI/RAR) Submission Slide 12 Duncan Ho, Qualcomm Incorporated
August 2023 doc.: IEEE 802.11-23/1884r0 SP1 Do you agree to define a mechanism in 11bn to enable a UHR non-AP MLD to transition from one AP MLD to another without requiring reassociation and encryption keys negotiation? Submission Slide 13 Duncan Ho (Qualcomm), et. al.,
August 2023 doc.: IEEE 802.11-23/1884r0 SP2 Do you agree to define a roaming mechanism in 11bn that enables a non-AP MLD, during roaming, to receive buffered DL MPDUs from its serving AP MLD and new DL MPDUs from the target AP MLD concurrently The serving AP MLD and the target AP MLD are non-colocated new DL MPDUs correspond to the DL MSDUs that are delivered from the DS to the target AP MLD for the non-AP MLD during (and after) roaming Submission Slide 14 Duncan Ho (Qualcomm), et. al.,
August 2023 doc.: IEEE 802.11-23/1884r0 SP3 Do you support to define that when a non-AP MLD roams from one AP MLD to another AP MLD, the context related to the non-AP MLD is transferred from one AP MLD to the other AP MLD such that it preserves the data exchange context for the non-AP MLD? Details of the context that can be transferred are TBD How to transfer the context is TBD. For example, the transfer of context can occur over the backhaul Submission Slide 15 Duncan Ho (Qualcomm), et. al.,
August 2023 doc.: IEEE 802.11-23/1884r0 SP4 Do you agree to define a roaming mechanism in 11bn that enables a non-AP MLD or its serving AP MLD to initiate roaming? Submission Slide 16 Duncan Ho (Qualcomm), et. al.,
