1. Delayed Acknowledgement v.s. Normal Acknowledgement
November 2001
Delayed Acknowledgement v.s. Normal Acknowledgement
Yasuo HARADA, Tan Pek Yew
Matsushita Electric Ind.
John Kowalski and Yoshihiro Ohtani
Sharp Corp.
Toshihiro Fujita
Sony Corp.
Harada Yasuo, Matsushita Electric Ind.

2. November 2001
Introduction
Sharp, Panasonic and Sony Requires High Bandwidth AV Transmission over IEEE802.11e
AV data of up to 24 Mbps
Reasonably reliable AV Data transmission at MAC
Current Draft offers 4 types of Acknowledgement policies:
Delay ACK offers low overheads with reasonable reliability
We find option of Delay ACK meets our requirement for AV Data transmission
Harada Yasuo, Matsushita Electric Ind.

3. Content This presentations demonstrates
November 2001
Content
This presentations demonstrates
The simple buffering mechanism needed for Delay ACK
It frees complex buffering mechanism at layer above MAC for High Data traffic (such as 24 Mbps AV Stream)
Simulation results of Delay ACK vs. Normal ACK
Two Scenarios are performed
0% PER &
10% PER
Harada Yasuo, Matsushita Electric Ind.

4. Implementation example for Delayed Acknowledgement
November 2001
Implementation example for Delayed Acknowledgement
Needs to:
Allocate fixed size of buffer to store transmitted packets that have not being acknowledged.
Update acknowledged buffer entries on upon reception of delayed ACK
Set retransmitted data packet to higher priority
Remove buffered data packet if it is not being acknowledged after delay bound
Stop pull for MSDU when buffer size is full
Harada Yasuo, Matsushita Electric Ind.

5. Implementation example for Delayed Acknowledgement (con’t)
November 2001
Implementation example for Delayed Acknowledgement (con’t)
Receiver Needs to:
Allocate fixed size of buffer to store out of sequence data frames
Transmit delayed acknowledgement after received certain numbers of data packets
Set delayed acknowledgement frame to higher priority
Keep acknowledgement history up to certain size
Deliver buffered packets that are in sequence at the head of the list to upper layer when buffer is full.
For example as shown in the following figure, the receiver buffer will be filled up after received packet ID 10. So, Packet ID 2 to 4 will be delivered to upper layer, even through Packet ID 1 is still not yet being received. Error handling for this case is upper layer decision.
Harada Yasuo, Matsushita Electric Ind.

6. A example of Delayed Acknowledgement Transmission Sequence
November 2001
A example of Delayed Acknowledgement Transmission Sequence
Fix Delayed ACK to always follow TXOP
TXOP
CF-Poll
QoS P P
CF-Poll
QoS P
Delayed
ACK
AP/HC
Data
QoS S
Data
QoS S
Data
QoS S
Data
QoS
Sender
Harada Yasuo, Matsushita Electric Ind.

7. TX & RX Buffering Mechanism
November 2001
TX & RX Buffering Mechanism
Upper Layer
Fill in N-8
Data Frames
Upper Layer
Fetch Data Frames with
TC-Seq 54 and 55
To upper layers & De-allocate
Memory for Seq 54 & 55
Buffer Size =
N Buffer Frames
Receiver
Buffer Cleared
Sender
TC-Seq = 54
TC-Seq = 56
TC-Seq = 55
TC-Seq = 57
TC-Seq = 58
TC-Seq = 59
TC-Seq = 58
TC-Seq = 60
TC-Seq = 61
TC-Seq = 60
TC-Seq = 62
TC-Seq = 61
TC-Seq = 63
TC-Seq = 62
TC-Seq = 63
Delay ACK Message Payload Received after receiving 10 Data Frames
Empty
Data Not Received
UnACK
ACK
TX to upper Layer
Harada Yasuo, Matsushita Electric Ind.

8. One example of Delayed ACK Transmission Sequence
November 2001
One example of Delayed ACK Transmission Sequence
TXOP
TXOP
TXOP
TXOP
Legend
Poll
Poll
Poll
Poll
SIFS
AP/HC
PIFS
Poll
QoS
CF-Poll 1 2 3 4 5 6 7 8 9 1 3 7 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8
Sender 1
QoS
Data
QoS
Data (Retransmission) 3
1st D ACK
2nd D ACK
Receiver
D ACK
Delayed
ACK
1st Delayed ACK
2nd Delayed ACK
Error in transmission
Before Received 1st Delayed ACK
After Received 1st Delayed ACK
Before Received 2nd Delayed ACK
After Received 2nd Delayed ACK
Sender Buffer 1 2 3 4 5 6 7 8 9 1 3 7 3 7 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 2 1 6
Data Seq 1 and 2 are being delivered to upper layer
Receiver Buffer 4 5 6 8 9 1
Data Seq 3 to 11 are being delivered to upper layer 1 3 1 4 1 5 1 7 1 8
Harada Yasuo, Matsushita Electric Ind.

9. Simulation Aim Scenario
November 2001
Simulation
Aim
Compare MSDU throughput of the following acknowledgement policy:
Normal Acknowledgement
Delayed Acknowledgement
Scenario
AP/HC poll a wireless station using QoS CF-Poll at the rate of 250 polls per sec
Sender: Wireless station (send at full rate)
Receiver: AP/HC (acknowledgement generator)
MSDU size = 1402 bytes, PHY Rate = 36Mbps OFDM
Harada Yasuo, Matsushita Electric Ind.

10. Normal Acknowledgement
November 2001
Normal Acknowledgement
ACK
Data
PER = 0%
PER = 10%
Harada Yasuo, Matsushita Electric Ind.

11. Delay Acknowledgement
November 2001
Delay Acknowledgement
Delayed ACK
Data
Configuration:
Duplication History Length = 64
a Delayed ACK is being generated after received 10 data frames
Retransmission Time: 0.001s, Receiver Buffer Size: 200 frames
PER = 0%
PER = 10%
Harada Yasuo, Matsushita Electric Ind.

12. November 2001
Summary
Delay-Ack Policy perform effective high data transmission for AV data transmission
Yasuo Harada et.al., Matsushita Electric Ind.