Doc.: IEEE 802.11-01/272a Submission June 2001 S. Choi, Philips Research Slide 1 Problems with IEEE...

June 2001

S. Choi, Philips ResearchSlide 1

doc.: IEEE 802.11-01/272a

Submission

Problems with IEEE 802.11(e) Problems with IEEE 802.11(e) NAV Operation NAV Operation

and ONAV Proposaland ONAV Proposal

Javier del Prado, Sunghyun Choi, and Amjad Soomro

Philips Research-USABriarcliff Manor, New York

[email protected]

June 2001


doc.: IEEE 802.11-01/272a

Submission

• Introduction• The Overlapping BSS problem• NAV rules under HCF • Limitations of NAV rules when OBSS• ONAV proposal

OutlineOutline

June 2001


doc.: IEEE 802.11-01/272a

Submission

Introduction Introduction Importance of NAVThe OBSS problem

Overlapping NAV (ONAV)

June 2001


doc.: IEEE 802.11-01/272a

Submission

HCF Relies on NAVHCF 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

June 2001


doc.: IEEE 802.11-01/272a

Submission

The OBSS problemThe 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

June 2001


doc.: IEEE 802.11-01/272a

Submission

We need another counter...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

June 2001


doc.: IEEE 802.11-01/272a

Submission

The Network Allocation VectorThe Network Allocation Vector(NAV)(NAV)

NAV Rules under HCF(See document 01/373r0)

June 2001


doc.: IEEE 802.11-01/272a

Submission

Setting NAV under HCFSetting 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

June 2001


doc.: IEEE 802.11-01/272a

Submission

Resetting NAV under HCFResetting 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

June 2001


doc.: IEEE 802.11-01/272a

Submission

Adjusting NAV under 802.11eAdjusting 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))]

June 2001


doc.: IEEE 802.11-01/272a

Submission

NAV Problems in 802.11-1999NAV Problems in 802.11-1999when OBSS existswhen OBSS exists

RTS/CTSCF-END(+)

June 2001


doc.: IEEE 802.11-01/272a

Submission

AP1 AP2

1STA ,12STA ,1

• STA1,2 is the 2nd STA in BSS 1.

1STA ,2

Overlapping BSS: ExampleOverlapping BSS: Example

June 2001


doc.: IEEE 802.11-01/272a

Submission

Potential NAV Reset after RTSPotential 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.”

June 2001


doc.: IEEE 802.11-01/272a

Submission

RTS Problem: ExampleRTS Problem: Example• STA1,2 reset NAV during CFP

U1 + ACK

STA1,2

Reception

Transmission

D1 + Poll AP1

STA2,1

RTS

NAV STA1,2

RTS duration

RESET NAV

CFP in BSS1

TBTT signaling aCFP in BSS1

B

2 x SIFS + CTS_Time + 2

x Slot

June 2001


doc.: IEEE 802.11-01/272a

Submission

NAV Reset per CF-EndNAV Reset per CF-End

• The CF-END problem– Current rule: Reset NAV upon reception of

CF-END– CF-END can come from an OBSS

June 2001


doc.: IEEE 802.11-01/272a

Submission

NAV Problems in 802.11e QoS Draft D1NAV Problems in 802.11e QoS Draft D1when OBSS existswhen OBSS exists

RTS/CTSCF-End

June 2001


doc.: IEEE 802.11-01/272a

Submission

Inherited from 802.11-1999Inherited 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

June 2001


doc.: IEEE 802.11-01/272a

Submission

NAV Invalidated by HCNAV 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

June 2001


doc.: IEEE 802.11-01/272a

Submission

The Overlapping Network The Overlapping Network Allocation Vector (ONAV)Allocation Vector (ONAV)

Operation Rules under HCF

June 2001


doc.: IEEE 802.11-01/272a

Submission

Setting ONAV 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

June 2001


doc.: IEEE 802.11-01/272a

Submission

Setting ONAV (II) 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.

June 2001


doc.: IEEE 802.11-01/272a

Submission

Frames from OBSS?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)

June 2001


doc.: IEEE 802.11-01/272a

Submission

Frames from OBSS? (II)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

June 2001


doc.: IEEE 802.11-01/272a

Submission

Resetting ONAVResetting 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)

June 2001


doc.: IEEE 802.11-01/272a

Submission

Adjusting ONAVAdjusting 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))]

June 2001


doc.: IEEE 802.11-01/272a

Submission

Limitations of the ONAVLimitations 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

June 2001


doc.: IEEE 802.11-01/272a

Submission

Transmission Rules Using Transmission Rules Using NAV and ONAVNAV and ONAV

Operation rules using NAV and ONAV

Solving the NAV limitations

June 2001


doc.: IEEE 802.11-01/272a

Submission

Using NAV and ONAVUsing 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

June 2001


doc.: IEEE 802.11-01/272a

Submission

Rules using NAV and ONAVRules 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

June 2001


doc.: IEEE 802.11-01/272a

Submission

Rules using NAV and ONAV (II)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

June 2001


doc.: IEEE 802.11-01/272a

Submission

Solving the RTS/CTS problemSolving the RTS/CTS problem

CFP in BSS1


B

U1 + ACK

ESTA1,2

Reception

Transmission

D1 + Poll AP1

STA2,1

RTS

NAV ESTA1,2

RTS duration

Revert ONAV2 x SIFS +

CTS_Time + 2 x Slot

ONAV ESTA1,2

June 2001


doc.: IEEE 802.11-01/272a

Submission

Solving the CF-END problemSolving the CF-END problem

CFP in BSS1


BESTA1,2

Reception

Transmission

ESTA1,2

AP1 Poll OBSSCF-END

NAV ESTA1,2

ESTA RESET ONAV

AP1

CF-END

LEGACY RESET NAV

ESTA1,1

AP1 Poll

PIFS

(ONAV was set previously in the CP)

ONAV ESTA1,2

June 2001


doc.: IEEE 802.11-01/272a

Submission

Moreover...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

Doc.: IEEE 802.11-01/272a Submission June 2001 S. Choi, Philips Research Slide 1 Problems with IEEE...

Documents

Transcript of Doc.: IEEE 802.11-01/272a Submission June 2001 S. Choi, Philips Research Slide 1 Problems with IEEE...