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Dynamic BSS Condition

Dynamic BSS Condition. Matthew Fischer Broadcom. Proposal to Remedy NO comments. Legacy BSS causes ERP BSS to use legacy slot – all BSS in a chain of overlapping ERP BSS fall like dominoes When legacy BSS disappears, entire chain of ERP BSS is stuck at legacy slot, cannot revert

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Dynamic BSS Condition

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  1. Dynamic BSS Condition Matthew Fischer Broadcom

  2. Proposal to Remedy NO comments • Legacy BSS causes ERP BSS to use legacy slot – all BSS in a chain of overlapping ERP BSS fall like dominoes • When legacy BSS disappears, entire chain of ERP BSS is stuck at legacy slot, cannot revert • Mixing of dynamic vs static bits in elements

  3. Objectives • Limit propagation of 802.11g directive information (short slot and protection required) found in beacons and probe responses to a physical extent of no more than one hop beyond the originator of the directive. • Separate static capability information from dynamic STA-directive information. • Change the name of the NonERP Information Element to Dynamic BSS Condition Element

  4. Objectives (2) • Extend Dynamic BSS Condition Element required usage to beacon and probe response transmissions by 802.11g STA in IBSS. • Establish rules for setting of bits PREQ and USESSLOT of Dynamic BSS Condition Element • Establish rules for setting GSTA bit of Capability Information Element

  5. Objectives (3) • Establish rules of propagation of received Dynamic BSS Condition Element information • Establish rules for ageing of information in received Dynamic BSS Condition Elements

  6. Locked Legacy Slot Problem (1) • 2 TGg BSS overlapping • Operating with short slot ERP1 ERP2

  7. Locked Legacy Slot Problem (2) • Legacy IBSS appears • Causing ERP1 to drop to legacy slot…. • Causing ERP2 to drop to legacy slot Legacy IBSS ERP1 ERP2

  8. Locked Legacy Slot Problem (3) • Legacy IBSS disappears • ERP1 remains at legacy slot, because adjacent ERP2 is operating at legacy slot, and vice versa… ERP1 ERP2

  9. Dynamic vs Static • Capability Element, currently defined: • Short Slot – dynamic – other bits are all static • NonERP Indication Element, currently defined: • Mitigation instructions – dynamic (from AP) – static (from STA, sort of) • Propose to: • Move all static together • Move all dynamic together

  10. 1 0 2 3 4 5 6 7 8 9 10 11 12 13 14 15 ESS IBSS CF Poll Req Priv-acy Short Pre-amble CCK- OFDM CF Poll-able PBCC Channel Agility Short Slot Octets 2 Figure 27 Capability information Field Updated Capability Element • Capability element: • Add gsta bit – to identify Legacy and non-Legacy • More properly, to discriminate 802.11g from non 802.11g • Make ShortSlot Capability = now STATIC Gsta

  11. Use of gsta bit • Rather than rely on presence or absence of nonERP Indication Element • Use gsta bit to determine if a beacon/PR came from legacy STA

  12. 1 0 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Prop gdir Octets 2 Figure xx Dynamic BSS Condition Field Updated nonERP Element • Change name to Dynamic BSS Condition Element • propgdir = Propagate G Directives (I.e. same as “I directly observed a NonG device”) • Instruction to the recipient of the element • preq = protection required • Usesslot = Use short slot preq Use sslot

  13. Propagation of Directives • Domino problem is due to unlimited propagation of directives • Limit propagation to one hop • Covers the hidden node interferer possibilities • Accomplished with propgdir bit • Fixes locked legacy-slot problem • Other solution is to never propagate directives (I.e. 0 hops) • I.e. only respond to legacy STA that you can directly observe

  14. Propagation of Information • Use one-hop propagation of info: • Determine local values for D_propgdir, D_preq and D_usesslot, based on local information (D_ = desired) • I.e. gsta bit = 0 in RX beacon/PR OR presence of associated legacy STA forces D_propgdir = 1, else 0 • Determine values for L_propgdir, L_preq and L_usesslot based on OR of all received propgdir, preq and usesslot bits, respectively (L_ = local = mybss) • Corresponding F_ bits for foreign (Vs local)

  15. TX Values • Determine values to be transmitted (T_ = transmitted): • T_propgdir = D_propgdir • T_preq = D_preq + R_preq * R_propgdir • T_usesslot = D_usesslot * (R_usesslot + !R_propgdir)

  16. STA behavior • STA shall use protection mechanism if S_PREQ is TRUE • AP: s_preq = t_preq • STA in BSS: s_preq = d_preq + l_preq • STA in IBSS: s_preq = d_preq + l_preq + f_preq

  17. STA behavior (2) • STA shall use short slot if S_USESSLOT is TRUE • AP: s_usesslot = t_usesslot • STA in BSS: s_usesslot = d_usesslot + l_usesslot • STA in IBSS: s_usesslot = d_usesslot + l_usesslot + f_usesslot

  18. Ageing Received Information • Age Received information with timeouts • Timeout value 30 sec

  19. Include IBSS • The proposed text includes IBSS in the mechanisms to discover non-802.11g devices and generate and propagate directives in response to this information

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