1. NAV Protection Mathilde Benveniste Avaya Labs, Research July 2003
doc.: IEEE /457
NAV Protection
Mathilde Benveniste
Avaya Labs, Research
July 2003

2. doc.: IEEE /457
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
The NAV rules do not protect QBSS properly when OBSS exists
M. Benveniste -- Avaya Labs, Research

3. HCF Polling NAV Reset HC overrules the NAV values
doc.: IEEE /457
July 2003
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

4. EDCF NAV Reset This is rooted from 802.11-1999
doc.: IEEE /457
July 2003
EDCF NAV Reset
This is rooted from
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

5. July 2003
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

6. July 2003
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

7. July 2003
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