1. Comment Resolution Regarding MDAOP End and NAV Clearing
May 2007
Comment Resolution Regarding MDAOP End and NAV Clearing
Date:
Authors:
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Michelle Gong, Cisco

2. Outline Background Comments regarding the start and the end of MDAOP
May 2007
Outline
Background
Comments regarding the start and the end of MDAOP
Suggested resolution
Michelle Gong, Cisco

3. The start and the end of MDAOP can set and reset NAVs in MDA devices
May 2007
The start and the end of MDAOP can set and reset NAVs in MDA devices
Section MDA Opportunity (MDAOP)
“This can be done by setting their NAVs for the duration of the MDAOP at the beginning of the MDAOP”
Section Access during MDAOPs
“At the beginning of an MDAOP that is not owned by the MP (it is not the transmitter) but is part of the Neighborhood MDAOP Times, the MP sets its NAV to the end of the MDAOP. Instead of setting the NAV, it can also use other means to not initiate a new transmission sequence during the MDAOP. The NAV setting may be reduced to a shorter time on the receipt of either a QoS+CF-Poll frame with a duration of 0 or a CF-end frame.”
Michelle Gong, Cisco

4. NAV clearing with CF-End resets NAVs in all neighboring MPs
May 2007
NAV clearing with CF-End resets NAVs in all neighboring MPs
Resetting NAVs is a double-edged sword
On one hand, every node that hears this CF-End frame will reset its NAV and can immediately start transmitting
On the other hand, “legitimate” NAVs can also be cleared. If an MDA MP has updated its NAV based on newly received packets, clearing its NAV will result in collisions.
CF-End frames also resets NAVs in non-MDA MPs mistakenly
Non-MDA MPs do not set their NAVs at the beginning of the MDAOP since they do not recognize MDA-related signaling
Michelle Gong, Cisco

5. Clearing NAVs in all neighboring MPs can result in collisions
May 2007
Clearing NAVs in all neighboring MPs can result in collisions
Node 4 starts to transmit after its NAV is reset by node 2, causing a collision at node 1
Time
Node 4
NAV
DATA
0 to 1
2 to 3 3
Node 2 and 3: MDA MPs 1 4 2
Node 0, 1 and 4: any MPs
Michelle Gong, Cisco

6. Clearing NAVs in all neighboring MPs can result in collisions
May 2007
Clearing NAVs in all neighboring MPs can result in collisions
Node 4 starts to transmit after its NAV is reset by node 2, causing a collision at node 1
Time
Node 4
NAV
DATA
0 to 1
DATA
2 to 3 3
Node 2 and 3: MDA MPs 1 4 2
Node 0, 1 and 4: any MPs
Michelle Gong, Cisco

7. Clearing NAVs in all neighboring MPs can result in collisions
May 2007
Clearing NAVs in all neighboring MPs can result in collisions
Node 4 starts to transmit after its NAV is reset by node 2, causing a collision at node 1
Time
Node 4
NAV
DATA
ACK
0 to 1
DATA
ACK
2 to 3 3
Node 2 and 3: MDA MPs 1 4 2
Node 0, 1 and 4: any MPs
Michelle Gong, Cisco

8. Clearing NAVs in all neighboring MPs can result in collisions
May 2007
Clearing NAVs in all neighboring MPs can result in collisions
Node 4 starts to transmit after its NAV is reset by node 2, causing a collision at node 1
Time
Node 4
NAV
DATA
ACK
DATA
0 to 1
DATA
ACK
CF-End
2 to 3 3
Node 2 and 3: MDA MPs 1 4 2
Node 0, 1 and 4: any MPs
Michelle Gong, Cisco

9. Clearing NAVs in all neighboring MPs can result in collisions
May 2007
Clearing NAVs in all neighboring MPs can result in collisions
Node 4 starts to transmit after its NAV is reset by node 2, causing a collision at node 1
Time
Node 4
NAV
DATA
ACK
DATA
DATA
0 to 1
DATA
ACK
CF-End
2 to 3 3
Node 2 and 3: MDA MPs 1 4 2
Node 0, 1 and 4: any MPs
Michelle Gong, Cisco

10. Clearing NAVs in all neighboring MPs can result in collisions
May 2007
Clearing NAVs in all neighboring MPs can result in collisions
Node 4 starts to transmit after its NAV is reset by node 2, causing a collision at node 1
Time
NAV
DATA
Node 4
DATA
ACK
DATA
0 to 1
DATA
ACK
CF-End
2 to 3 3
Node 2 and 3: MDA MPs 1 4 2
Node 0, 1 and 4: any MPs
Michelle Gong, Cisco

11. MDA devices do not need to set their NAVs during MDAOPs
May 2007
MDA devices do not need to set their NAVs during MDAOPs
As already described in Section , “Instead of setting the NAV, it can also use other means to not initiate a new transmission sequence during the MDAOP. ”
The current text is confusing and clarification/rewording of the text is necessary
The following procedures can achieve the same effect as setting and resetting the NAVs
An MP that is not the owner of an MDAOP shall not transmit during the advertised MDAOP
At the end of MDAOP, MPs can resume data transmission
An MDA MP refrains from transmitting either when its NAV setting is non-zero or during someone else’s MDAOP
Michelle Gong, Cisco

12. May 2007
Clarification and rewording of the text are needed to address the following comments
Comments on MDAOP start and MDAOP NAV setting
CIDs 1530, 1536, 1539, 2187, 3550, 3556, 3822, 4205
Comments on truncating MDAOP and MDAOP NAV clearing
CIDs
Michelle Gong, Cisco

13. May 2007
Suggested Resolution
Clarify that NAV setting and NAV clearing are not needed at the start and the end of an MDAOP
For instance, it can be simply stated that “An MP that is not the owner of the advertised MDAOP shall not transmit during the duration of MDAOP.”
Instead of using CF-End, a new action frame can be defined to end the current MDAOP
Michelle Gong, Cisco