1 / 8

Long Slot Directive

Long Slot Directive. Matthew Fischer Broadcom mfischer@broadcom.com. D4.0 - Long Slot Use. Switch to long slot When long-slot STA associates When knowledge of neighboring co-channel long-slot BSS exists Causes lock-up problem if a legacy device wanders in, then leaves

karli
Download Presentation

Long Slot Directive

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Long Slot Directive Matthew Fischer Broadcom mfischer@broadcom.com Matthew Fischer, Broadcom

  2. D4.0 - Long Slot Use • Switch to long slot • When long-slot STA associates • When knowledge of neighboring co-channel long-slot BSS exists • Causes lock-up problem if a legacy device wanders in, then leaves • 2 or more G-BSS overlapping • Legacy device causes cascade of switching to long slot • G-BSS’s reinforce each other’s long slot state after legacy device leaves Matthew Fischer, Broadcom

  3. Solution to Lock-up • Establish Short Slot as default operation • AP reverts to Long Slot operation when: • A long-slot STA is associated • A co-channel legacy BSS is detected • No longer need neighboring BSS using long slot rule which included Long Slot G-BSS • Long Slot G-BSS will be covered by LSTT updates • But place time limit on long slot operation • LSTT = Long Slot Termination Time (1 second?) • Send LSTT in outgoing beacons, use latest LSTT Matthew Fischer, Broadcom

  4. AP (+ IBSS STA) behavior • Rules for switching to Long Slot • If Long-slot associated, or legacy BSS sighted • At TBTT, before beaconing • If Long Slot required according to local conditions, compute local required time duration for long slot • TBTT+MLSE • MLSE = Minimum Long Slot Epoch = ~1 second? • If TBTT+MLSE > LSTT • Update LSTT <= TBTT+MLSE • Else, no change to LSTT • Send LSTT in outgoing beacons, PR frames Matthew Fischer, Broadcom

  5. STA+AP behavior • Keep track of latest received LSTT • update to “latest” of received LSTT values • Not “last received” but “latest long slot epoch end-time” • I.e. similar to NAV update – use “later” of local and received values • At all times: If LSTT>TSF • Use Long Slot, otherwise, revert to Short Slot • Unless your associated AP has ShortSlot=0 Matthew Fischer, Broadcom

  6. RX “foreign” beacon • Beacon contains TSF and LSTT • Easy to calculate delta from time of beacon reception to foreign LSTT • Use delta to adjust foreign LSTT to local TSF time-base • Compare foreign LSTT to local LSTT • Update as appropriate Matthew Fischer, Broadcom

  7. LSTT Minimum Resolution • Resolution must be less than: • Minimum separation between • Receipt of beacon • Transmission of beacon • I.e., must guarantee that all STA TSF will have advanced by at least one LSTT tick between TX of any LSTT and next possible RX of LSTT • To insure that LSTT does not get constantly pushed forward • Otherwise, two AP may trade same LSTT indefinitely • (would require constant beaconing to occur…) Matthew Fischer, Broadcom

  8. The bits • ShortSlot bit in capability element • No longer a directive – really only a capability • Add LSTT field to nonERP indication element: • 1 bit – LSTTValid • Need this or some reserved value, (0x000000?), to indicate valid LSTT field • 23 bits - LSTT • Allows MLSE up to 4.19 seconds • MLSE cannot exceed LSTTbits minus one • To allow wrap detection • To deal with TSF deltas among STA • May consider longer MLSE – to allow more hops Matthew Fischer, Broadcom

More Related