Long Slot Directive Matthew Fischer Broadcom mfischer@broadcom.com November 2002 doc.: IEEE 802.11-00/xxx November 2002 Long Slot Directive Matthew Fischer Broadcom mfischer@broadcom.com Matthew Fischer, Broadcom Matthew Fischer, Broadcom

D4.0 - Long Slot Use Switch to long slot When long-slot STA associates November 2002 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

Solution to Lock-up Establish Short Slot as default operation November 2002 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

AP (+ IBSS STA) behavior November 2002 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

STA+AP behavior Keep track of latest received LSTT November 2002 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 Matthew Fischer, Broadcom

RX “foreign” beacon Beacon contains TSF and LSTT November 2002 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

LSTT Minimum Resolution November 2002 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

The bits ShortSlot bit in capability element November 2002 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