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NAV Protection. Mathilde Benveniste Avaya Labs, Research July 2003. NAV protection. Current NAV protection is not adequate to provide reliable virtual carrier sensing The NAV of a station should be set or reset by considering all stations or functions involved

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NAV Protection

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Nav protection

NAV Protection

Mathilde Benveniste

Avaya Labs, Research

July 2003


Nav protection1

NAV protection

  • Current NAV protection is not adequate to provide reliable virtual carrier sensing

  • The NAV of a station should be set or reset by considering all stations or functions involved

  • The NAV rules do not protect QBSS properly when OBSS exists

M. Benveniste -- Avaya Labs, Research


Hcf polling nav reset

HCF Polling NAV Reset

  • HC overrules the NAV values

    • HC can reset NAV of QSTAs by sending CF-END

    • HC can reset NAV of QSTAs by sending QoS (+)CF-poll to itself with Dur/ID = 0

      Source: 11-01/272

M. Benveniste -- Avaya Labs, Research


Edcf nav reset

EDCF NAV Reset

  • This is rooted from 802.11-1999

    • 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 STA may reset the NAV.

      Source: 11-01/272

M. Benveniste -- Avaya Labs, Research


Nav problem

NAV Problem

Several sources of NAV setting; the NAV should be set always to the longest value.

The problem arises when NAV must be reset because a source requests so. How can we know which source set the NAV in order to cancel it?

M. Benveniste -- Avaya Labs, Research


Nav problem solution

NAV Problem Solution

Define NA: address TXOP holder causing NAV to be set

Keep a set of the n highest NAV values, ANAV. For each NAV retain the NA of the node setting it.

When an HC sets the NAV, the NA is the address of the HC

When the NAV is set through an RTS, the NA is the address of the station sending the RTS

In general, a station will refrain from transmitting if a ANAV component >0

When a component of ANAV expires it becomes 0

A new NAV is retained among the n ANAV components if it exceeds the length of the shortest NAV retained, which it replaces.

Reset the ANAV component of the source requesting reset. Set a ANAV[NA]=0 when NA coincides with the address of a node responsible for NAV cancellation

M. Benveniste -- Avaya Labs, Research


Nav use

NAV Use

A station will not respond to a poll if any ANAV component other than that associated with its HC/BSS is positive.

A station will acknowledge receipt of a successful transmission regardless of the ANAV values.

M. Benveniste -- Avaya Labs, Research


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