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Problems with IEEE 802.11(e) NAV Operation and ONAV Proposal

Problems with IEEE 802.11(e) NAV Operation and ONAV Proposal. Javier del Prado, Sunghyun Choi, and Amjad Soomro Philips Research-USA Briarcliff Manor, New York sunghyun.choi@philips.com. Outline. Introduction The Overlapping BSS problem NAV rules under HCF

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Problems with IEEE 802.11(e) NAV Operation and ONAV Proposal

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  1. Problems with IEEE 802.11(e) NAV Operation and ONAV Proposal Javier del Prado, Sunghyun Choi, and Amjad Soomro Philips Research-USA Briarcliff Manor, New York sunghyun.choi@philips.com S. Choi, Philips Research

  2. Outline • Introduction • The Overlapping BSS problem • NAV rules under HCF • Limitations of NAV rules when OBSS • ONAV proposal S. Choi, Philips Research

  3. Introduction Importance of NAV The OBSS problem Overlapping NAV (ONAV) S. Choi, Philips Research

  4. HCF Relies on NAV • The CFB and CFP are protected by NAV • NAV even more important under HCF due to: • Direct ESTA-to-ESTA transmissions • Multiple frame exchanges during TxOP • Power control will be possible per 802.11h • Problem • NAV does not protect QBSS properly when OBSS exists S. Choi, Philips Research

  5. The OBSS problem • The presence of an OBSS can result in collisions even under HCF • NAV should work for this purpose • But, the current rules present some limitations when there are OBSSs S. Choi, Philips Research

  6. We need another counter... • We need to solve the NAV limitations when there are OBSSs • We also need to protect the QBSS from OBSSs, especially under HCF ONAV: The Overlapping Network Allocation Vector under HCF S. Choi, Philips Research

  7. The Network Allocation Vector(NAV) NAV Rules under HCF (See document 01/373r0) S. Choi, Philips Research

  8. Setting NAV under HCF • No change from the current rules • Including the followings • During the CP/CFB/CFP • Update NAV with the Duration/ID field from a QoS (+)CF-Poll if the new NAV value is larger than the old value • During the CFP • Non-HC ESTAs preset NAV to CFPMaxDuration at TBTT in which a CFP starts • Non-HC ESTAs shall update their NAV using the CFPDurRemaining value S. Choi, Philips Research

  9. Resetting NAV under HCF • During a CFB in the CP • Reset upon reception of QoS (+)CF-Poll addressed to the HC with Duration/ID field equal to 0 • Reset upon reception of a data frame with the NF bit equal to 0 and with the SA equal to TxOP holder address as well as the subsequent QoS CF-ACK if the normal ACK policy is used. • During the CFP • Upon reception of a CF-END coming from its own BSS S. Choi, Philips Research

  10. Adjusting NAV under 802.11e • During the CP/CFB/CFP • ESTA that uses the Dur/ID field from an RTS frame to update its NAV may save the previous value of NAV. If no PHY-RXSTART.indication is detected from the PHY during a period with a duration of (2 x aSIFSTime) + (CTS_Time) + (2 x aSlotTime) starting at the PHY-RXEND.indication corresponding to the detection of the RTS frame, the ESTA may set the NAV with the following value: max [0, old NAV value – ((2 x aSIFSTime) + (CTS_Time) + (2 x aSlotTime))] S. Choi, Philips Research

  11. NAV Problems in 802.11-1999when OBSS exists RTS/CTS CF-END(+) S. Choi, Philips Research

  12. STA 1 ,2 AP AP 1 2 STA 2 ,1 STA 1 ,1 Overlapping BSS: Example • STA1,2 is the 2nd STA in BSS 1. S. Choi, Philips Research

  13. Potential NAV Reset after RTS • Clause 9.2.5.4 of 802.11-1999 reads: “STA that used information from an RTS frame as the most recent basis to update its NAV setting is permitted to reset its NAV if no PHY-RXSTART.indication is detected from the PHY during a period with a duration of (2 ´ aSIFSTime) + (CTS_Time) + (2 ´ aSlotTime) starting at the PHY-RXEND.indication corresponding to the detection of the RTS frame.” S. Choi, Philips Research

  14. TBTT signaling a CFP in BSS1 STA2,1 B AP1 RTS D1 + Poll U1 + ACK CFP in BSS1 RTS duration 2 x SIFS + CTS_Time + 2 x Slot RESET NAV RTS Problem: Example • STA1,2 reset NAV during CFP STA1,2 Reception Transmission NAV STA1,2 S. Choi, Philips Research

  15. NAV Reset per CF-End • The CF-END problem • Current rule: Reset NAV upon reception of CF-END • CF-END can come from an OBSS S. Choi, Philips Research

  16. NAV Problems in 802.11e QoS Draft D1when OBSS exists RTS/CTS CF-End S. Choi, Philips Research

  17. Inherited from 802.11-1999 • NAV reset after RTS still possible • This is fixed by 01/373r0 though • Reset NAV per CF-End still problematic • CF-End from the same QBSS reset NAV • But, this could result in collisions with OBSS S. Choi, Philips Research

  18. NAV Invalidated by HC • HC overrules the NAV values • ESTA shall respond to QoS (+)CF-Poll during CFB/CFP even with non-zero NAV • HC can reset NAV of ESTAs by sending QoS (+)CF-poll to itself with Dur/ID = 0 • By having OBSS running HCF, a QBSS is not protected by NAV • ESTAs in OBSS may work independent of the NAV value per its HC ruling found above S. Choi, Philips Research

  19. The Overlapping Network Allocation Vector (ONAV) Operation Rules under HCF S. Choi, Philips Research

  20. Setting ONAV • Transition from CP to CFB/CFP • If an ESTA receives a QoS (+)CF-Poll and its NAV or ONAV is non-zero, save the value of max(NAV, ONAV) in the ONAV counter, and set the NAV using the Duration/ID field specified in the QoS (+)CF-Poll frame. • At TBTT when a CFP is scheduled to start, if an ESTA has non-zero NAV, the ESTA shall save the value of max(NAV, ONAV) in the ONAV counter, and set the NAV to dot11CFPMaxDuration S. Choi, Philips Research

  21. Setting ONAV (II) • During CFB/CFP • Upon reception of a valid frame, which has been determined to come from an OBSS, the ESTA shall update their ONAV using the Duration/ID field, but only when the new ONAV value is greater than the current ONAV. When an ESTA updates its ONAV, that ESTA also saves the MAC address from the BSSID field if it is present in the frame. • For a frame reception, either NAV or ONAV (not both) may be updated. S. Choi, Philips Research

  22. Frames from OBSS? • Can check via BSSID in frames • Problem: RTS, CTS and ACK frames don’t carry BSSID • We need a rule to detect where the frame is coming from (see next) S. Choi, Philips Research

  23. Frames from OBSS? (II) • TXsrc: Tx Source address • TXsrc = MAC address of HC by default • TXsrc = DA of a QoS (+)CF-Poll received • TXsrc reverts to HC address when NAV becomes 0 • For each frame without BSSID field • If RTS: compare the SA of the RTS with TXsrc • If CTS or ACK: compare the DA of the CTS or ACK with TXsrc If SARTS or DACTS,ACK = TXsrc The frame is coming from the own QBSS S. Choi, Philips Research

  24. Resetting ONAV • Upon reception of one of the following frames that arrived from the OBSS that last updates the ONAV: • QoS CF-Poll addressed to the HC with a Duration/ID field equal to 0 • QoS Data(+) frame with the NF bit equal to 0 or • CF-END (If the ONAV was last updated with an RTS, CTS or ACK frame, the ESTA does not know which OBSS last updated the ONAV. In this case, the ESTA shall reset the ONAV when it receives one of the frames listed above that has arrived from any alien BSS, irrespective of the value of the BSSID) S. Choi, Philips Research

  25. Adjusting ONAV • ESTA that uses the Dur/ID field from an RTS frame to update its ONAV may save the previous value of ONAV. If no PHY-RXSTART.indication is detected from the PHY during a period with a duration of (2 x aSIFSTime) + (CTS_Time) + (2 x aSlotTime) starting at the PHY-RXEND.indication corresponding to the detection of the RTS frame, the ESTA may set the ONAV with the following value: max [0, old ONAV value – ((2 x aSIFSTime) + (CTS_Time) + (2 x aSlotTime))] S. Choi, Philips Research

  26. Limitations of the ONAV • More than one overlapping BSS • ONAV can only track the OBSSs if the BSSID is received in the frame that updates it. • If ONAV updated and saved BSSID, reset ONAV when a CF-Poll with the Dur/ID equal to 0, Data with NF=0 or CF-END is received from the OBSS • IF ONAV updated with RTS,CTS or ACK, reset ONAV whenever a CF-Poll with the Dur/ID field equal to 0, Data with NF=0 or CF-END is received from any OBSS S. Choi, Philips Research

  27. Transmission Rules Using NAV and ONAV Operation rules using NAV and ONAV Solving the NAV limitations S. Choi, Philips Research

  28. Using NAV and ONAV • Conditions: • Operation under HCF(ONAV not updated during non-CFB Contention Period) • All the ESTAs can hear from the HC • NAV updated ONLY with frames coming from its BSS • ONAV updated with frames coming from an OBSS • Contention allowed only when both counters are 0 S. Choi, Philips Research

  29. Rules using NAV and ONAV • In the non-CFB Contention Period • An ESTA can contend for the medium and respond to RTS only if both NAV and ONAV are zero • If ESTA receives QoS (+)CF-Poll frame, only respond with QoS Data(+) to the Poll if NAV and ONAV are zero. • However, always generate QoS CF-ACK frame upon successful reception of a frame that requires acknowledgement irrespective of NAV/ONAV values S. Choi, Philips Research

  30. Rules using NAV and ONAV (II) • In the CFB/CFP • Respond to QoS (+)CF-Poll and RTS from the TxOP holder only when the ONAV is zero • Always generate QoS CF-ACK frame upon successful reception of a frame that requires acknowledgement S. Choi, Philips Research

  31. TBTT signaling a CFP in BSS1 STA2,1 B RTS AP1 D1 + Poll U1 + ACK CFP in BSS1 RTS duration Revert ONAV 2 x SIFS + CTS_Time + 2 x Slot Solving the RTS/CTS problem Reception ESTA1,2 Transmission NAV ESTA1,2 ONAV ESTA1,2 S. Choi, Philips Research

  32. TBTT signaling a CFP in BSS1 AP1 Poll AP1 Poll OBSS AP1 B ESTA1,2 ESTA1,1 CF-END CF-END PIFS CFP in BSS1 LEGACY RESET NAV ESTA RESET ONAV Solving the CF-END problem Reception ESTA1,2 Transmission NAV ESTA1,2 ONAV ESTA1,2 (ONAV was set previously in the CP) S. Choi, Philips Research

  33. Moreover... • ONAV can be a good solution for avoiding unnecessary collisions with OBSSs • It protects my QBSS from OBSSs • When ESTAs in OBSSs use ONAV, my QBSS is protected • To be fair to OBSSs, my ESTAs should use ONAV as well • And provides fairness to the OBSSs • Enables fair bandwidth share among OBSSs S. Choi, Philips Research

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