1. BlockAck Enhancement for Multicast Transmissions
November 2007
2/22/2019May 2008
doc.: IEEE /2752r1
BlockAck Enhancement for Multicast Transmissions
Date:
Authors:
Hang Liu, et. al, Thomson Inc.
Peter Ecclesine, Cisco Systems

2. November 2007
2/22/2019May 2008
doc.: IEEE /2752r1
Abstract
This contribution proposes BlockAck enhancements to improve link reliability for multicast/broadcast transmissions
Hang Liu, et. al, Thomson Inc.
Peter Ecclesine, Cisco Systems

3. Outlines Problems for Multicast in 802.11
November 2007
2/22/2019May 2008
doc.: IEEE /2752r1
Outlines
Problems for Multicast in
Multicast BlockAck with Immediate Policy
Multicast BlockAck with Delayed Policy
Multicast BlockAck with PSMP
Hang Liu, et. al, Thomson Inc.
Peter Ecclesine, Cisco Systems

4. Problems for Multicast/Broadcast in 802.11
2/22/2019May 2008
Problems for Multicast/Broadcast in
Collision in the BSS (intra-BSS Collision)
The associated STAs transmit when an AP is transmitting multicast/broadcast frames
Overlapping BSS (OBSS) Collision (Inter-BSS Collision)
The STAs/APs in OBSSes transmit when an AP is transmitting multicast/broadcast frames
Hidden node problem
Link transmission errors
No ACK
Collision S2 S1 S1
Collision S7
AP1
AP2 S5 S4 S3 S6 S3 S2
AP2 is a hidden node to AP1
Hang Liu, et. al, Thomson Inc.

5. Multicast BlockAckReq with Immediate Block Ack Policy
Multicast Block Ack exchange
Multicast data block
(BAR control, BAR Info, Receiver Info)
Sender/AP
Frame-exchange
for NAV Protection
Data
Data
M-Block
AckReq
M-Block
Ack
Receiver/STA1
Receiver/STA 2
M-Block
Ack
Receiver/STA 3
Not included in the BlockAck-requested receiver list
Multicast BlockAckReq (M-BlockAckReq) contains a list of BlockAck-requested receiver identifiers (in the form of receiver bitmap control and partial virtual bitmap field)
The STAs send their M-BlockAck in the order that they are specified in the receiver bitmap of the M-BlockAckReq
Hang Liu, et. al, Thomson Inc.

6. Multicast BlockAck and Retransmission
M-BlockAckReq or M-BlockAck may be lost
If AP does not successfully receive the M-BlockAcks from all the intended recipient STAs, then
retransmits the M-BlockAckReq with the remaining STAs in the receiver bitmap field from which the M-BlockAck have not received
the remaining STAs respond with an M-BlockAck in the order listed in the M-BlockAckReq receiver bitmap
this process is repeated until the AP receives M-BlockAcks from all the intended STAs or the number of retransmission attempts has reached to a limit.
After M-BlockAckReq and M-BlockAck exchanges, the AP determines from the information in the received M-BlockAck bitmap whether a frame needs to be retransmitted.
If a frame is lost (not correctly received by one or more intended multicast recipient STAs), the AP arranges the retransmissions of the lost frame.
The retransmitted frames are sent multicast
After retransmitting the lost frames and/or transmitting new frames, the AP can initiate a new M-BlockAckReq and M-BlockAck exchange to obtain the receiving status of (re)transmitted frames.
This retransmission process can be repeated for a lost frame until all the intended recipient STAs that sent the M-BlockAck receive the frame correctly or the lifetime of this frame expires.
Hang Liu, et. al, Thomson Inc.

7. M-BlockAckReq Frame
Frame
Control
Duration
/ID
Receiver
Information RA TA
BAR Control
BAR
Information
FCS
BAR Receiver Bitmap Control
BAR Receiver Partial Bitmap
Type/Flags
BAR receiver bitmap control subfield (1 octet): Bitmap Offset Value N = STA’s AID divided by 16
Bit 0 reserved and bits 1-7 Bitmap Offset
Each bit in the BAR receiver partial virtual bitmap subfield corresponds to a specific station
Bit i corresponds to the STA with an AID of 16 x N + i.
The length of partial virtual bitmap varies and is a multiple of octets, which can be determined from the total frame size.
If bit i in the receiver bitmap field is set to 1, then the station with AID 16 x N + i is requested to reply to this M-BlockAckReq with M-BlockAck,
Hang Liu, et. al, Thomson Inc.

8. M-BlockAck Frame Frame Control BA Information Duration/ID RA TA
BA Control
FCS
BA Ack Policy
Multi-
TID
Compressed
Bitmap
Multi-
cast
Reserved
TID_Info
BA Control Field
Block Ack Starting Sequence Control
BA Information field
(BlockAck or Compressed BlockAck)
Block Ack Bitmap
Block Ack Starting Sequence Control
BA Information field
(Multi-TID BlockAck)
Per TID Info
Block Ack Bitmap
Hang Liu, et. al, Thomson Inc.

9. M-BlockAckReq & M-BlockAck Exchange Sequence with Delayed Policy and Ack
Multicast Block Ack Request and ACK
Delayed multicast Block Ack and ACK
Multicast data block
Sender/AP
(BAR Control, BAR Info, Receiver Info)
Frame-exchange
for NAV Protection
Data
Data
M-Block
AckReq
Ack
Ack
M-Block
Ack
Ack
Receiver/STA 1
Ack
M-Block
Ack
Receiver/STA 2
Receiver/STA 3
Not included in the block ack-requested receiver list
Hang Liu, et. al, Thomson Inc.

10. Delayed multicast Block Ack Multicast Block Ack Request
M-BlockAckReq &M-BlockAck Exchange Sequence with Delayed Policy and No Ack
Delayed multicast Block Ack
Multicast data block
Multicast Block Ack Request
Sender/AP
(BAR Control, BAR Info, Receiver Info)
Frame-exchange
for NAV Protection
Data
Data
M-Block
AckReq
M-Block
Ack
Receiver/STA 1
M-Block
Ack
Receiver/STA 2
Receiver/STA 3
Not included in the blockack-requested receiver list
Hang Liu, et. al, Thomson Inc.

11. M-BlockAckReq & M-BlockAck Exchange Sequence with PSMP
MP Originator /AP
Downlink phase
PSMP
Multicast Data Block
Other multicast or unicast data blocks
Multi-cast Data
Multi-cast Data
M-Block
AckReq
Uni-cast data
STA 1 uplink data block
Uplink phase
M-Block
Ack
Up-link data
Receiver/STA 1
STA 2 uplink data block
M-Block
Ack
Receiver/STA 2
STA 3 uplink data block
Up-link data
Receiver/STA 3
Not included in the blockack-requested receiver bitmap of M-BlockAckReq
Hang Liu, et. al, Thomson Inc.

12. Thank You!
Questions?
Hang Liu, et. al, Thomson Inc.