Multicast/Broadcast Communication With Acknowledge February 2008 doc.: IEEE 802.11-07/2376r0 November 2008 Multicast/Broadcast Communication With Acknowledge Date: 2008-11-04 Authors: Liwen Chu Etc. Liwen Chu, STMicroelectronics

February 2008 doc.: IEEE 802.11-07/2376r0 November 2008 Abstract Audio video requires reliable transmissions and deterministic delay. Currently, it is difficult to provide reliable audio video transmissions in 802.11 because of the poor support of broadcast/multicast transmission, and because EDCA cannot provide a deterministic delay guarantee. This contribution proposes the use of blockAck based methods to provide reliable audio video transmission. The proposed methods do not require any physical layer modifications. Liwen Chu Etc. Liwen Chu, STMicroelectronics

MAC Enhancements in VTS PAR November 2008 MAC Enhancements in VTS PAR Graceful degradation of audio video streams when there is insufficient channel capacity, by enabling packet discarding without any requirement for deep packet inspection, Increased robustness in OBSS environments, without the requirement for a centralised management entity, Intra-Access Category prioritization of transport streams by modifying EDCA timing and parameter selection without any requirement for deep packet inspection, Improved link reliability and low jitter characteristics for multicast/broadcast audio video streams, Interworking with relevant 802.1AVB mechanisms (802.1Qat, 802.1Qav, 802.1AS) Liwen Chu Etc.

Reasons why Broadcast/Multicast is Unreliable November 2008 Reasons why Broadcast/Multicast is Unreliable Intra BSS collision: Associated STAs transmit frames when an AP is transmitting broadcast/multicast frames. Inter BSS collision (OBSS collision): OBSS STAs/APs transmit frames when an AP is transmitting broadcast/multicast frames. No feedback to indicate the correct reception of the broadcast/multicast frames AP Collision! AP2 Collision! AP1 STA4 STA1 STA3 STA1 STA2 STA3 STA6 STA2 STA5 Collision! Inter BSS collision Intra BSS (OBSS) collision Liwen Chu Etc.

Methods to make Broadcast/Multicast Reliable November 2008 Methods to make Broadcast/Multicast Reliable Decrease the probability of a broadcast/multicast collision. Add feedback to broadcast/multicast frames. Liwen Chu Etc.

Feedback for a Single Multicast/broadcast Frame November 2008 Feedback for a Single Multicast/broadcast Frame An AP selects a single STA to feedback an ACK to the multicast/broadcast frame. It is the most efficient, but least reliable solution. An AP selects many STAs to feedback ACK frames and specifies the sequence for the replies (start offset, duration). It is a less efficient solution, since more than one ACK will respond to a multicast/broadcast frame, but is more reliable. Liwen Chu Etc.

Feedback for Multiple (BlockAck) Multicast/broadcast Frames November 2008 Feedback for Multiple (BlockAck) Multicast/broadcast Frames An AP must maintain a multicast/broadcast blockAck (MBBA) group (the AP and all STAs of the multicast/broadcast blockAck destinations are defined as a MBBA group). STA joining procedure STA leaving procedure MBBA group teardown procedure An AP must select STAs to reply with blockAcks using blockAck request. An AP allocates the start offset and duration of the blockAck replies. Liwen Chu Etc.

Multicast/broadcast Joining/Leaving Procedure November 2008 Multicast/broadcast Joining/Leaving Procedure A STA with the capability to join an MBBA group sends an Add multicast/broadcast blockAck (ADDMBBA) Request frame to the AP. After receiving an ADDMBBA Request frame, an AP replies with an ADDMBBA Response frame to the STA with the capability to join an MBBA group in order to complete the joining. If a STA wants to leave an MBBA group, it uses a Leave multicast/broadcast blockAck (LVMBBA) frame to tell an AP that it will leave the MBBA group. Liwen Chu Etc.

MBBA Group Teardown Procedure November 2008 MBBA Group Teardown Procedure If an AP wants to tear down the group, it sends via unicast/multicast/broadcast a Leave multicast/broadcast blockAck (LVMBBA) frame to each STA in the MBBA group. If all STAs have left a MBBA group, the AP tears down the MBBA group. Liwen Chu Etc.

Multicast/Broadcast BlockAck Procedure November 2008 Multicast/Broadcast BlockAck Procedure Multicast/broadcast BlockAck only support the immediate blockAck policy. An AP uses MBBA Request (MBBAReq) frames to request all or part of destination STAs to respond MBBA Ack frames MBBAReq can be defined as following: BlockAckReq with multicast/broadcast receiving address is MBBAReq. BlockAckReq uses Bit 11 in BAR Control field to indicate weather this BlockAckReq is MBBAReq or normal (unicast) BlockAckReq. A new control frame is allocated for MBBAReq. MBBA Request frame indicates when a STA will reply a MBBA Ack frame The following fields are required in MBBAReq in addition to the fields in BlockAckReq frame: AID (STA identifier) MBBA Ack start offset The start offset is the offset relative to the start of MBBA Req frame MBBA Ack duration The duration is used for MBBA Ack transmission Liwen Chu Etc.

Multicast/Broadcast BlockAck Example November 2008 Multicast/Broadcast BlockAck Example AP1, STA1, STA2, STA3 are in a MBBA group. AP1 STA1 STA3 STA2 STA4 Multicast Data Frames Backoff MBBA Req AP1 MBBA Ack STA1 MBBA Ack STA2 MBBA Ack STA3 MBBA TXOP Liwen Chu Etc.

Multicast/Broadcast BlockAck Retransmission Procedure November 2008 Multicast/Broadcast BlockAck Retransmission Procedure When many of the indicated STAs do not receive the multicast/broadcast frames correctly, an AP may use the MBBA mechanism to retransmit the multicast/broadcast frames. A STA which receives the multicast/broadcast frames more than once will discard the repeated frames, but must reply with an MBBA Ack frame if requested by the AP. When a few of the indicated STAs do not receive the multicast/broadcast frames correctly, an AP may use the normal blockAck procedure to retransmit the frames to the STA. When only a few frames need to be retransmitted, an AP may send frames with normal ack policy. Liwen Chu Etc.

Multicast/Broadcast BlockAck Retransmission Example November 2008 Multicast/Broadcast BlockAck Retransmission Example AP1, STA1, STA2, STA3 are in a MBBA group. AP1 STA1 STA3 STA2 STA4 BA: BlockAck Backoff Backoff MBBA Req AP1 BA Req Multicast Data Frames MBBA Ack Multicast Data Frames STA1 MBBA Ack STA2 MBBA Ack corrupted STA3 BA MBBA TXOP Normal BlockAck for Retransmission Liwen Chu Etc.

Possible MBBA Collision November 2008 Possible MBBA Collision Non protected MBBA TXOP may have a high chance to collide with other transmission. BlockAck recommend to use RTS/CTS, HCCA etc. protection mechanism to protect the blockAck transmission. STA7 Collision! AP2 STA4 STA6 STA5 AP1 STA1 STA3 STA2 Backoff Backoff AP1 MBBA Req BA Req Multicast Data Frames MBBA Ack Multicast Data Frames STA1 MBBA Ack STA2 Corrupted MBBA Req Corrupted frames STA3 BA MBBA TXOP Normal BlockAck for Retransmission Backoff Backoff STA5 Liwen Chu Etc.

MBBA TXOP Protection Methods November 2008 MBBA TXOP Protection Methods Before the MBBA txop, an AP can select more than one MBBA group member and use MBBA Req/MBBA Ack to protect the MBBA TXOP. MBBA TXOP Backoff MBBA Req MBBA Req AP1 MBBA Ack Multicast Data Frames MBBA Ack STA1 MBBA Ack MBBA Ack STA2 MBBA Ack STA3 Protection Stage Broadcast/Multicast Tx Stage AP2 STA4 STA6 STA5 AP1 STA1 STA2 STA3 AP3 STA7 STA8 STA9 Liwen Chu Etc.

MBBA TXOP Protection Methods (Cont’d) November 2008 MBBA TXOP Protection Methods (Cont’d) Before the MBBA txop, an AP can select a MBBA group member and use RTS/CTS to protect the MBBA TXOP. MBBA TXOP Backoff MBBA Req AP1 RTS Multicast Data Frames MBBA Ack STA1 MBBA Ack STA2 CTS MBBA Ack STA3 Protection Stage Broadcast/Multicast Tx Stage AP2 STA4 STA6 STA5 AP1 STA1 STA2 STA3 Liwen Chu Etc.

MBBA TXOP Protection Methods (Cont’d) November 2008 MBBA TXOP Protection Methods (Cont’d) An AP selects one or more STAs that transmit protection frames in the protection stage to neighboring OBSS. An 802.11k neighbor report or other method may be used to select STAs to transmit protection frames. The selected STAs should cover all neighboring OBSS in order to minimize collisions. Liwen Chu Etc.

PSMP TXOP Protection Methods November 2008 PSMP TXOP Protection Methods PSMP can be used as reliable multicast/broadcast communication. But PSMP need protection before PSMP transmission to avoid OBSS collision. Method 1: before the PSMP TXOP, an AP can select more than one multicast group member and use PSMP/Null frame (other protection frames may be used instead) to protect the PSMP TXOP. No downlink data frames are transmitted. The uplink duration only allows a null frame to be transmitted. If there are buffered frames to the AP, the STA will respond with a null frame to request more uplink TXOP. If there is no buffered frame, the STA will respond with a null frame to indicate no buffered frames. Method 2: before the PSMP TXOP, an AP can select a multicast group member and use RTS/CTS (protection frame) to protect the PSMP TXOP. Liwen Chu Etc.

PSMP TXOP Protection Methods (Cont’d) November 2008 PSMP TXOP Protection Methods (Cont’d) An AP selects one or more STAs that transmit protection frames in the protection stage to neighboring OBSS. An 802.11k neighbor report or other method may be used to select STAs to transmit protection frames. The selected STAs should cover all neighboring OBSS in order to minimize collisions. Liwen Chu Etc.

PSMP TXOP Protection Methods (Cont’d) November 2008 PSMP TXOP Protection Methods (Cont’d) MBBA TXOP Backoff AP1 PSMP PSMP Null frame Multicast Data Frames STA1 MTBA STA1 Null frame STA2 MTBA STA2 STA3 MTBA STA3 Protection Stage Broadcast/Multicast Tx Stage AP2 STA4 STA6 STA5 AP1 STA1 STA2 STA3 AP3 STA7 STA8 STA9 Liwen Chu Etc.

PSMP TXOP Protection Methods (Cont’d) November 2008 PSMP TXOP Protection Methods (Cont’d) MBBA TXOP Backoff AP1 RTS PSMP Multicast Data Frames STA1 MTBA STA1 STA2 MTBA STA2 CTS STA3 MTBA STA3 Protection Stage Broadcast/Multicast Tx Stage AP2 STA4 STA6 STA5 AP1 STA1 STA2 STA3 Liwen Chu Etc.

Multiple BlockAckReq/BlockAck (Leader) Based TXOP Protection Methods November 2008 Multiple BlockAckReq/BlockAck (Leader) Based TXOP Protection Methods Multiple BlockAckReq/Blockack in a TXOP can be used as reliable multicast/broadcast communication. But multiple BlockAck TXOP need protection before PSMP transmission to avoid OBSS collision. Method 1: before the Multiple BlockAck TXOP, the AP can select more than one multicast group member and use multiple RTS/CTS or modified RTS (multicast RTS)/CTS (other protection frames may be used instead) to protect the PSMP TXOP. After receiving multicast RTS, multicast destinations return CTS based on the sequence indicated by the AP. Method 2: before the Multiple BlockAck TXOP, the AP can select a multicast group member and use RTS/CTS (protection frame) to protect the Multiple BlockAck TXOP. Liwen Chu Etc.

November 2008 Multiple BlockAckReq/BlockAck (Leader) Based TXOP Protection Methods (Cont’d) An AP selects one or more STAs that transmit protection frames in the protection stage to neighboring OBSS. An 802.11k neighbor report or other method may be used to select STAs to transmit protection frames. The selected STAs should cover all neighboring OBSS in order to minimize collisions. Liwen Chu Etc.

November 2008 Multiple BlockAckReq/BlockAck (Leader) Based TXOP Protection Methods (Cont’d) MBBA TXOP Backoff BA Req BA Req BA Req AP1 RTS RTS Multicast Data Frames STA1 CTS BA STA2 CTS BA STA3 BA Protection Stage Broadcast/Multicast Tx Stage Backoff AP1 MRTS AP2 STA4 STA6 STA5 AP1 STA1 STA2 STA3 AP3 STA7 STA8 STA9 STA1 CTS STA2 CTS STA3 Protection Stage Liwen Chu Etc.

November 2008 Multiple BlockAckReq/BlockAck (Leader) Based TXOP Protection Methods (Cont’d) MBBA TXOP Backoff BA Req BA Req BA Req AP1 RTS Multicast Data Frames STA1 BA STA2 CTS BA STA3 BA Protection Stage Broadcast/Multicast Tx Stage AP2 STA4 STA6 STA5 AP1 STA1 STA2 STA3 Liwen Chu Etc.

Protection Methods for Reserved Multicast TXOP November 2008 Protection Methods for Reserved Multicast TXOP An AP can reserve TXOP for video communication (HCCA etc.). Before the multicast video transmission in a reserved TXOP, STAs selected by the AP can transmit CTS2Self to protect the video transmission. An AP selects one or more STAs that transmit protection frames in the protection stage to neighboring OBSS. An 802.11k neighbor report or other method may be used to select STAs to transmit protection frames. The selected STAs should cover all neighboring OBSS in order to minimize collisions. Liwen Chu Etc.

Multicast/Broadcast Sequence Number an BlockAck Buffer Release November 2008 Multicast/Broadcast Sequence Number an BlockAck Buffer Release A QoS AP assigns sequence number using a single modulo-4096 counter for multicast/Broadcast frames, management frames, non-QoS frames. A recipient can not distinguish a lost multicast/broadcast data frame from a management frame, non-QoS frame or a frame of other group. A transmitter may not be able to transmit a block of frames with the total number being equal to the negotiated buffer size for a group address. A STA may have a unicast blockAck agreement and multicast/broadcast blockAck agreement for the same TID at the same time. The reorder buffer of a multicast/broadcast blockAck should not be identified by TA/TID. The blockAck buffer may not be released in time. STA3 STA4 AP STA1 STA2 Liwen Chu Etc.

Fast Multicast/Broadcast Buffer Release November 2008 Fast Multicast/Broadcast Buffer Release The reorder buffer of a multicast/broadcast blockAck should be identified by group address(RA)/TID. An AP may send a BlockAckReq/MBBA/MTBA to shift the recipient’s starting sequence number past the hole in the SN space that is created by management frame, non-QoS frame, and/or frames of other group. This can release multicast/broadcast buffer right away and allow the earliest possible passing of buffered frames up to the next MAC process. This can guarantee that the transmitter and the receivers have the same start sequence number of the transmit buffer and the receiver buffer. This can avoid the receiver wrongly discard multicast frames. Liwen Chu Etc.

November 2008 Backup Slides Liwen Chu Etc.

Delayed Multicast/Broadcast Buffer Release November 2008 Delayed Multicast/Broadcast Buffer Release The transmitting buffer size and receiving size of blockAck buffers are all 4. STA1 and STA2 are one multicast group. STA3 and STA4 are another multicast group. x x 3 STA4 3 x x 3 STA4 STA3 STA3 3 AP 1 2 3 4 AP 1 2 x 4 STA1 1 2 4 STA1 STA2 1 2 x 4 STA2 1 2 4 Liwen Chu Etc.

Delayed Multicast/Broadcast Buffer Release November 2008 Delayed Multicast/Broadcast Buffer Release The transmitting buffer size and receiving size of blockAck buffers are all 4. STA1 and STA2 are one multicast group. STA3 and STA4 are another multicast group. x x 3 STA4 3 x x 3 STA3 STA4 STA3 3 BA Req AP 1 2 3 4 AP 1 2 x 4 STA1 1 2 4 BA STA1 STA2 1 2 x 4 STA2 1 2 4 Liwen Chu Etc.

Delayed Multicast/Broadcast Buffer Release November 2008 Delayed Multicast/Broadcast Buffer Release The transmitting buffer size and receiving size of blockAck buffers are all 4. STA1 and STA2 are one multicast group. STA3 and STA4 are another multicast group. x x 3 STA1 does not sends frame4 to up layer since it does not know that frame3 is for another group! STA4 3 x x 3 STA3 STA3 STA4 3 BA Req AP 1 2 3 4 AP x 4 STA1 1 2 4 BA STA1 STA2 1 2 x 4 STA2 1 2 4 Liwen Chu Etc.

Delayed Multicast/Broadcast Buffer Release November 2008 Delayed Multicast/Broadcast Buffer Release The transmitting buffer size and receiving size of blockAck buffers are all 4. STA1 and STA2 are one multicast group. STA3 and STA4 are another multicast group. STA1 and STA2 do not sends frame4 to up layer since they do not know that frame3 is for another group! x x 3 AP’s start sequence number for STA1/STA2 transmitting buffer is 5. The starting sequence number in STA1’s and STA2’s receiving buffers are 3. STA4 3 x x 3 STA3 STA3 STA4 3 BA Req BA Req AP 1 2 3 4 AP x 4 STA1 1 2 4 BA STA1 STA2 x 4 STA2 1 2 4 BA Liwen Chu Etc.

Delayed Fast Multicast/Broadcast Buffer Release November 2008 Delayed Fast Multicast/Broadcast Buffer Release The transmitting buffer size and receiving size of blockAck buffers are all 4. STA1 and STA2 are one multicast group. STA3 and STA4 are another multicast group. x x 3 AP’s start sequence number for STA1/STA2 transmitting buffer is 5. The starting sequence number in STA1’s and STA2’s receiving buffers are 3. STA4 3 x x 3 STA4 STA3 STA3 3 BA Req BA Req AP 1 2 3 4 5 AP x 4 5 STA1 1 2 4 BA 5 STA1 STA2 x 4 5 STA2 1 2 4 BA 5 Liwen Chu Etc.

Delayed Multicast/Broadcast Buffer Release November 2008 Delayed Multicast/Broadcast Buffer Release The transmitting buffer size and receiving size of blockAck buffers are all 4. STA1 and STA2 are one multicast group. STA3 and STA4 are another multicast group. x x 3 AP’s start sequence number for STA1/STA2 transmitting buffer is 5. The starting sequence number in STA1’s and STA2’s receiving buffers are 3. STA4 3 x x 3 STA3 STA4 STA3 3 BA Req BA Req AP 1 2 3 4 5 6 AP x 4 5 6 STA1 1 2 4 BA 5 6 STA1 STA2 x 4 5 6 STA2 1 2 4 BA 5 6 Liwen Chu Etc.

Delayed Multicast/Broadcast Buffer Release November 2008 Delayed Multicast/Broadcast Buffer Release The transmitting buffer size and receiving size of blockAck buffers are all 4. STA1 and STA2 are one multicast group. STA3 and STA4 are another multicast group. x x 3 AP’s start sequence number for STA1/STA2 transmitting buffer is 5. The starting sequence number in STA1’s and STA2’s receiving buffers are 3. STA4 3 x x 3 STA3 STA3 STA4 3 BA Req BA Req AP 1 2 3 4 5 6 7 AP x 4 5 6 Accepting it and adjusting starting SN Or discarding it? STA1 1 2 4 BA 5 6 STA1 STA2 x 4 5 6 Accepting it and adjusting starting SN Or discarding it? STA2 1 2 4 BA 5 6 Liwen Chu Etc.