1. Use of More Data Field Date: 2006-01-17 Authors: Jan 2006 Jan 2006
doc.: IEEE /0155r0
Jan 2006
Use of More Data Field
Date:
Authors:
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Jon Edney, Jari Jokela, Nokia
Jon Edney, Jari Jokela, Nokia

2. Jan 2006
doc.: IEEE /0155r0
Jan 2006
Abstract
This submission describes a modification to the use of the “More Data” field to enable the AP to signal the state of its transmission queue to stations that are not is power-save mode.
Jon Edney, Jari Jokela, Nokia
Jon Edney, Jari Jokela, Nokia

3. Review of basic Power Save Operation
Jan 2006
Review of basic Power Save Operation
The “More Data” bit is used to indicate that the AP has data waiting to be sent to the STA
STA gets an indication of waiting data in the “TIM”: part of a beacon sent at DTIM.
STA Polls AP for each MPDU
AP sends MPDU and sets “More data” bit if there are further MPDUs waiting to be sent
STA can keep polling until More Data bit is clear
The more data bit is not used unless STA is in power save mode
Jon Edney, Jari Jokela, Nokia

4. Jan 2006
Additions by e
Power save mechanism extended to allow for sending of prioritized traffic from both STA and AP side. Designed to ensure low priority data from AP does not block high priority data from STA
More Data bit can be set by QAP in ACK frame responding to data from QSTA
Otherwise usage is similar and only appropriate to stations in power save mode.
Jon Edney, Jari Jokela, Nokia

5. Jan 2006
New Proposal
To use “More Data” bit also with STAs that are not in PS mode to indicate that data is ready to be delivered
Purpose: To enable stations to delay the start of a transition until all pending data is delivered
Jon Edney, Jari Jokela, Nokia

6. Benefit Analysis We considered two types of traffic:
Jan 2006
Benefit Analysis
We considered two types of traffic:
Regular datagram type traffic (e.g. UDP)
Streaming data with window acknowledge (e.g. TCP)
Voice traffic might can use UDP to deliver a stream of packets at regular intervals
File transfer or Web page access uses TCP to allow efficient bulk transfer of data
Jon Edney, Jari Jokela, Nokia

7. Model for analysis Jan 2006 Packet Source Buffered Network Switch
Local
Switch
AP1
AP2
STA
Jon Edney, Jari Jokela, Nokia

8. Case 1: Constant Packet Rate (Datagram)
Jan 2006
Case 1: Constant Packet Rate (Datagram)
Packet
Source
Buffered
Network
Switch
Low aggregate utilization
Low buffer requirement in network or AP
Unlikely the “More Data” bit will be set
Local
Switch
AP1
AP2
STA
Jon Edney, Jari Jokela, Nokia

9. Case 2: Streaming in busy network
Jan 2006
Case 2: Streaming in busy network
Packet
Source
Buffered
Network
Switch
Source sends
“TCP window” worth
of data
Due to network congestion or
rate limitation TCP window
is buffered in network
Packet Source generates TCP window of data
Packets are buffered in network router due to congestion
Packets are released at fairly constant rate
“More Data” Bit unlikely to be set
Local
Switch
AP1
AP2
STA
Jon Edney, Jari Jokela, Nokia

10. Case 3: Streaming in hi-capacity network
Jan 2006
Case 3: Streaming in hi-capacity network
Packet
Source
Buffered
Network
Switch
Source sends
“TCP window” worth
of data
Packet Source generates TCP window of data
Packets pass quickly to AP - AP buffers the window
Packets are released at fairly constant rate
“More Data” Bit likely to be set
Problem is that packets will always be queue until file transfer is completed.
Might be better to transition now and wait for resend of entire window to AP2
Local
Switch
AP1
AP2
STA
Jon Edney, Jari Jokela, Nokia

11. Jan 2006
Initial Conclusion
For station operating in power active mode the use of “More Data” has some value:
For regular (e.g. VoIP) traffic frames will not queue at AP
For Streaming in busy network, frames queue in network - not AP
For Streaming is fast network frames will queue in AP - but More Data bit will not clear until completion of TCP transfer
However.... we need to consider case where STAs use power save
Jon Edney, Jari Jokela, Nokia

12. Consequences of PS Mode
Jan 2006
Consequences of PS Mode
In power save mode STA might only wake-up every DTIM to receive beacons and check for data
In case 1, STA is unlikely to be in PS mode because each datagram must be processed in timely manner
In case 3, STA is unlikely to be in PS mode because data is constantly arriving
In case 2 STA wants to go to PS mode after emptying buffer. Several packets may accumulate before STA activates again
Jon Edney, Jari Jokela, Nokia

13. Case 3: Streaming in hi-capacity network
Jan 2006
Case 3: Streaming in hi-capacity network
Packet
Source
Buffered
Network
Switch
Source sends
“TCP window” worth
of data
Packet Source generates TCP window of data
Packets pass quickly to AP - AP buffers the window
Packets are released at fairly constant rate
Frames are queued at AP1 because STA is sleeping
STA switched to active mode to receive packets and prepare for transition
STA wants to know when queued frames are delivered.
More Data bit can inform the STA of the best time to transition.
Local
Switch
AP1
AP2
STA
Jon Edney, Jari Jokela, Nokia

14. Jan 2006
Conclusion
Use of More Data bit of significant value to stations preparing to transition when power save mode is in operation.
Jon Edney, Jari Jokela, Nokia

15. Key points of Normative Text
Jan 2006
Key points of Normative Text
Use of More Data bit only applies to Fast BSS STAs that are not in powersave mode.
Setting of More Data bit by Fast BSS AP is optional (at the APs discretion)
Use of More Data bit information by STA is not defined (although it is suggested it be used in the decision of when to transition)
Jon Edney, Jari Jokela, Nokia

16. Jan 2006
Motion
Move to adopt the text of r-use-more-data-bit.doc into the TGr Draft
Jon Edney, Jari Jokela, Nokia

17. References 11-05-0151-00-000r-new-twist-more-data-bit.ppt
Jan 2006
References
r-new-twist-more-data-bit.ppt
r-use-more-data-bit.doc
Jon Edney, Jari Jokela, Nokia