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Mechanisms for Transmission Suppression in 802.11

Mechanisms for Transmission Suppression in 802.11. Author: Matthew Sherman AT&T Labs - Research 180 Park Avenue Florham Park, NJ 07932 973-236-6791 mjsherman@att.com. Date: Jan 18, 2001. Problem addressed. 802.11e is developing mechanisms to support QoS

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Mechanisms for Transmission Suppression in 802.11

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  1. Mechanisms for Transmission Suppression in 802.11 Author: Matthew Sherman AT&T Labs - Research 180 Park Avenue Florham Park, NJ 07932 973-236-6791 mjsherman@att.com Date: Jan 18, 2001 Matthew Sherman, AT&T Labs - Research

  2. Problem addressed • 802.11e is developing mechanisms to support QoS • Many situations when the ability to cause groups of STA to cease transmissions would be useful • Accommodate TBTT for Beacon transmission • Overlapped BSS Mitigation • Accommodate protocol enhancements • HCF / Token passing schemes, Other • Would like technique applied to also work with Legacy STA (LSTA) • Would like ability to differentiate between Legacy and groups of 802.11e STA (ESTA) Matthew Sherman, AT&T Labs - Research

  3. Approach to Problem • Develop method to Set NAV in a STA group • Develop method to Reset NAV in a STA group • Use existing frame formats as much as possible • Enhances compatibility with LSTA Matthew Sherman, AT&T Labs - Research

  4. Approach to Problem (Cont.) • Played with interpretation of RTS, CTS, and CF-End messages • Had ESTA use Addresses for qualifiers and signaling • Apply Duration field based on contents of Addresses • Based signaling / qualifiers on Address types • Unicast • Multicast • Broadcast • Chose mappings that are consistent with current usage of address fields in standard Matthew Sherman, AT&T Labs - Research

  5. Suggested ECTS Mechanisms • Enhance CTS (ECTS) usage to allow setting Duration/ID field to any valid Duration value • Broadens context for Duration field use • Enhance CTS usage to allow any valid address in RA field • LSTA will always set NAV for duration indicated • Rules for ESTA will vary (See Chart) • Allow use of PIFS with this message for preferential media access (EAP only) Matthew Sherman, AT&T Labs - Research

  6. Map of New Capabilities (CTS) Matthew Sherman, AT&T Labs - Research

  7. Suggested ERTS Mechanisms • Enhance RTS (ERTS) usage to allow setting Duration/ID field to any valid Duration • Broadens context for Duration field use • Enhance RTS usage to allow any valid address in RA and TA fields • LSTA will always set NAV for duration indicated • Rules for ESTA will vary (See Chart) • Allow use of PIFS with this message for preferential media access (EAP only) Matthew Sherman, AT&T Labs - Research

  8. Map of New Capabilities (RTS) Matthew Sherman, AT&T Labs - Research

  9. Suggested ECF-End Mechanisms • Enhance CF-End (ECF-End) usage to allow any valid address in RA and TA fields • Allow use of ECF-End outside CFP • LSTA always reset NAV when received • Rules for ESTA will vary (See Chart) • Allow use of PIFS with this message for preferential media access (EAP only) • Could also use “piggybacked” Ack Matthew Sherman, AT&T Labs - Research

  10. Map of New Capabilities (CF-End) Matthew Sherman, AT&T Labs - Research

  11. What Enhancements Accomplish • If no LSTA • Can set / reset NAV independently in any group of ESTA • Some ability to control remote groups via RTS/CTS relay • Since can have “Group” of one, can set for single ESTA as well • If LSTA are present • Must treat as special case • Sometimes part of addressed group, Sometimes not Matthew Sherman, AT&T Labs - Research

  12. A Special Case • May want to set NAV in ESTA Group but not LSTA • Use 2 message sequence • Send ECTS to Group • Group sets NAV • LSTA set NAV • Send ECF-End from broadcast • LSTA reset NAV • No ESTA reset NAV Matthew Sherman, AT&T Labs - Research

  13. Comments on Mechanisms • No new frame formats required • Fully backward-compatible • Tables presented are suggestions • Meant to show concept • Open to other usage mappings • Open to partial acceptance of mappings • Implementation of mechanisms could be optional • Some mapping mandatory in ESTA to be of use • Duration field in other frame types could also be used to reserve channel • RTS/CTS seemed most appropriate Matthew Sherman, AT&T Labs - Research

  14. Comments specific to Overlapped BSS • Goal of new mappings is to allow suppression of groups of terminals in overlap • Technique assumes ability exists to assign terminals to groups • Where is such a technique defined? • Are modifications required to support it? • Best if applied with ability to solicit interference info from STA • Which other STA are heard at what power level • What Management frame should be used for report? • Are new elements needed? Matthew Sherman, AT&T Labs - Research

  15. Other Mechanisms for Consideration • Allow side-traffic during CFP • Allows relay of “Proxy Beacon” and other messages when Disjoint CFPs exist between adjacent BSSs • Define ability of STA to relay messages • Already need for Proxy Beacon • Allow non-uniform Fragmentation during CFP • More efficient use of TxOPs Matthew Sherman, AT&T Labs - Research

  16. Example Applications of New Mechanisms Matthew Sherman, AT&T Labs - Research

  17. Example ECTS UsageReduction of TBTT Overrun* RA=Broadcast Legacy Tx Suppressed Beacon TxN ECTS B Tx1 Tx2 B ETx TBTT TBTT PIFS NAV Set by Legacy STA * Assumes ESTA knows not to overrun TBTT ETx is transmission by ESTA Matthew Sherman, AT&T Labs - Research

  18. Example ERTS Usage*Unscheduled CFP TA=Don’t Care RA=Broadcast Unsolicited Tx Suppressed Unscheduled CFP shortened by CF-End Prior Tx ERTS CF_Poll CF_Ack CF_End PIFS NAV Set by all STA NAV Reset by all STA * HFC may be better option. This is just a convenient example. Also shows use of CF_END to reset NAV and shorten Tx Suppression time Matthew Sherman, AT&T Labs - Research

  19. Example UsageHidden STA Suppression* TA=Group A RA=RSTA Beacon RA=Group A CFP B ERTS ECTS CF_Poll TBTT Hidden Node Suppressed * Assumes Hidden ESTA (HSTA) is in known group to begin with (Group A) Assume group same as for Relay ESTA (RSTA) Matthew Sherman, AT&T Labs - Research

  20. TA=Don’t Care RA=Broadcast RA=Group B Unscheduled CFP BSS1 Silent ERTS CF-Poll CF-End ECTS Tx Tx CF-End BSS2 Silent Unscheduled CFP ECTS Tx Tx CF-End ERTS CF-Poll CF-End RA=Group A TA=Don’t Care RA=Broadcast Example Usage - BSS Silent* BSS1 BSS2 * Assume ESTA that interfere from BSS2 to BSS1 are in group A Assume ESTA that interfere from BSS1 to BSS2 are in group B Matthew Sherman, AT&T Labs - Research

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