1. New Twist on More Data Bit
March 2005
doc.: IEEE /0151r0
March 2005
New Twist on More Data Bit
Date:
Authors:
Name
Organization
Jon Edney
Nokia
Jari Jokela
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Edney, Jokela - Nokia
Edney, Jokela - Nokia

2. March 2005
doc.: IEEE /0151r0
March 2005
Abstract
This submission presents a proposal to use the “More Data Bit” in MPDUs sent to active stations to give a hint about the status of queues in the sending AP and avoid lost frames on transition.
Edney, Jokela - Nokia
Edney, Jokela - Nokia

3. Loss of packets during transition
March 2005
Loss of packets during transition
It has been noted (doc 05/1646) that packets might be lost during a transition
Proposals have been made for schemes to avoid / prevent losses
Such schemes benefit from better knowledge of AP queue state
This submission proposes a simple method to communicate queue state
This can be used by itself to avoid, but not eliminate, packet loss
Edney, Jokela - Nokia

4. March 2005
Causes of lost packets
Packets are queued at the old access point but STA transitions away without waiting for delivery
Packets arrive over the DS after the STA has transitioned from the old AP but before the DS has been updated to route packets to the new AP
New frames go to wrong AP
DS not yet updated
HUB
AP1
AP2
STA has associated
STA
Edney, Jokela - Nokia

5. Reducing losses due to queued frames
March 2005
Reducing losses due to queued frames
If STA knows that Old AP has frames queued for delivery it can delay transition until frames are delivered
Therefore we need a way for AP to notify STA that is has queued frames
Mechanism already exists to do this in power save mode: the “More Data” bit
Propose to allow use of More Data Bit during active mode for TGr STAs
Edney, Jokela - Nokia

6. Use of More Data Bit in base standard
March 2005
Use of More Data Bit in base standard
When responding to PSPoll from STA in power save mode, AP sets More Data Bit if it has more frames queued for transmission to the STA.
AP sets More Data Bit in transmissions to both active and power save STAs during DTIM (broadcasts)
STA may set More Data Bit when responding to CF_Poll in contention free period.
Edney, Jokela - Nokia

7. Use of More Data Bit in Draft 802.11e
March 2005
Use of More Data Bit in Draft e
Operation of More Data Bit is extended for use with APSD power save mode
QAP can also signal to STA the there are queued frames in response to a frame sent from the STA by setting More Data Bit in ACK frames
Edney, Jokela - Nokia

8. Proposed extension (1) AP Behaviour (2) STA Behaviour
March 2005
Proposed extension
(1) AP Behaviour
When sending to a STA that supports TGr extensions….
the AP may set the More Data Bit in any directed MPDU transmission….
if the AP has any data frames queued for transmission to the STA
(2) STA Behaviour
While in active mode….
a TGr capable may read the More Data Bit on directed frames and use the information as part of a decision when to transition….
but is not required to do so.
Edney, Jokela - Nokia

9. Conclusion A small addition with a useful benefit
March 2005
Conclusion
A small addition with a useful benefit
Presented for discussion
If there is interest we will bring normative text after first draft of TGr has been created.
Edney, Jokela - Nokia

10. References 11-05-1646-00-000r-no-packet-left-behind.ppt March 2005
Edney, Jokela - Nokia