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[STDS-802-11-TGBE] Group addressed frames delivery discussion

Hi all,

 

Thanks for the comments and discussion today regarding my contribution 20/442r4 Group Addressed Frame Delivery for EHT.

 

I ran out of time to explain more so let me try to do it here based on the passed discussion and assumptions. Please let me know if you have any questions or comments.

 

  • Desirable behavior/requirement: Non-AP MLD will be able to receive these frames on any links for full flexibility for the non-AP MLD
  • Desirable behavior/requirement: The non-AP MLD selects to receive these frames but does not need to tell the AP MLD
  • => Agreed solution/path: the group addressed frames are duplicated and transmitted on all the links (since the AP doesn’t know a prior which link the non-AP MLD selects)

 

  • However, since these frames use different SN space on different links, the non-AP MLD will not be able to do any duplicate detection on two frames received from two different links
    • This is NOT  a problem *IF* the non-AP MLD doesn’t change the selected link
    • The duplicates or miss occurs only if the non-AP MLD changes link so the question is how to solve these two problems. Frames can be missed or duplicated during the link switch
    • To solve the “miss” problem, the non-AP MLD should avoid switching link in the middle of a group addressed frames delivery  on the selected link (a train of frames on that link being delivered)
    • To solve the “duplicate” problem, we added cross-link BU indication bcast on each link. The non-AP MLD should avoid switching link if the AP on the selected link indicates there are still BUs on the other links (because it may receive duplicated frames undetected otherwise)
      • Note the above duplicate avoidance is not 100% but should work well in most cases (where the group addressed delivery frames come sporadically as bursts and get duplicated to all links around the same time)
      • To solve the duplicate problem 100%, one obvious way is to use a common SN for all the frames but that option was met with heavy objections

 

Thanks,

Duncan

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