1. Matthew Fischer Broadcom
November 2001
September 2002
Dynamic BSS Condition
Matthew Fischer
Broadcom

2. Proposal to Remedy NO comments
September 2002
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. September 2002
Objectives
Limit propagation of g 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. September 2002
Objectives (2)
Extend Dynamic BSS Condition Element required usage to beacon and probe response transmissions by g 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. September 2002
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)
September 2002
Locked Legacy Slot Problem (1)
2 TGg BSS overlapping
Operating with short slot
ERP1
ERP2

7. Locked Legacy Slot Problem (2)
September 2002
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)
September 2002
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:
November 2001
September 2002
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. Updated Capability Element
September 2002
Updated Capability Element
Capability element:
Add gsta bit – to identify Legacy and non-Legacy
More properly, to discriminate g from non g
Make ShortSlot Capability = now STATIC
ESS
IBSS CF
Poll-able
Poll Req
Priv-acy
Short
Pre-amble
PBCC
Channel
Agility
CCK-
OFDM
Slot 1 9 2 3 4 5 6 7 8 10 11 12 13 14 15
Octets
Figure 27 Capability information Field
Gsta

11. November 2001
September 2002
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. Updated nonERP Element
September 2002
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
Prop
gdir 1 9 2 3 4 5 6 7 8 10 11 12 13 14 15
Octets
Figure xx Dynamic BSS Condition Field
preq
Use
sslot

13. Propagation of Directives
September 2002
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
September 2002
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):
September 2002
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
September 2002
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
September 2002
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
September 2002
Ageing Received Information
Age Received information with timeouts
Timeout value 30 sec

19. September 2002
Include IBSS
The proposed text includes IBSS in the mechanisms to discover non g devices and generate and propagate directives in response to this information