1. Proposed Modifications to 802.11e-D4.0 Group ACK
January 2003
Proposed Modifications to
802.11e-D4.0 Group ACK
Carlos Rios, RiosTek LLC

2. January 2003
D4.0 Group ACK Summary
Group ACK per e-D4.0 is a relatively involved protocol to allow QSTAs to burst transmissions to another QSTA while deferring any and all corresponding ACKs until after a later (Group) ACK request.
Upon association, sender QSTA gleans from (Association frame) Capabilities Info field that candidate receiver QSTA is capable of Group ACK
Group ACK is set up, characterized and torn down with Action Frames: Sender transmits ADDGA Request to set up GA with receiver Receiver responds with ADDGA Response to announce its GA capabilities
Sender and Receiver define Tx, Rx Buffer sizes and otherwise prep for GA
DELGA Request lets the sender tear down previously established GA capability
Once GA is set up, sender advertises any transmitted frames subject to GA by setting an appropriate flag in the packet MAC Header QOS Control field
Keeps track of all buffer sizes, etc so to not send too many packets, etc
Group ACKable frames are transmitted, separated by SIFS
Done transmitting the burst, Sender issues GroupACK Request Control frame
Receiver immediately responds with a Group ACK or an ACK
The ACK lets him mark time until he’s done preparing a real Group ACK
Needs to process Group ACK Req and correlate with his Rx buffer
Real Group ACK ready, receiver QSTA transmits it as soon as possible
Sender needs to ACK this Group ACK
Sender can then initiate another burst at his convenience

3. D4.0 Group ACK Shortcomings
January 2003
D4.0 Group ACK Shortcomings
GA functionality should be available to all stations, not just QSTAs
GAs should be allowed under DCF rules
SIFS Burst packet separation hard requirement is too restrictive
Indicates all GA packets need be queued at the sender
SIFS should be a minimum, goal separation
Don’t use QOS Control field to advertise GA parameters
Replace “Order” bit (B15) in MAC Header Frame Control field with a “No Immediate ACK” bit always set upon a Group ACK transmission
Modify Group ACK Request frame to simplify GA processing
GAReq frame now contains a “Start Sequence Control” field
Receiver and sender need calculate which sequence numbers were actually received from sender, which were actually sent to the receiver and, which, if any need be retransmitted
Much easier for the GAReq to contain the list of seqnos actually sent, and the GA to contain the list of seqnos actually received

4. Proposed Group ACK Modifications
January 2003
Proposed Group ACK Modifications
Modified Group ACK is a relatively involved protocol to allow a STA to burst transmissions to another STA while deferring any and all corresponding ACKs until after a later (Group) ACK request.
Upon association, sender STA gleans from (Association frame) Capabilities Info field that candidate receiver STA is capable of Group ACK
Group ACK is set up, characterized and torn down with Action Frames: Sender transmits ADDGA Request to set up GA with receiver Receiver responds with ADDGA Response to announce its GA capabilities
Sender and Receiver define Tx, Rx Buffer sizes and otherwise prep for GA
DELGA Request lets the sender tear down previously established GA capability
Once GA is set up, sender advertises any transmitted frames subject to GA by setting an appropriate flag in the packet MAC Header Frame Control field
Keeps track of all buffer sizes, etc so to not send too many packets, etc
Group ACKable frames are transmitted, separated at a minimum by SIFS
Done transmitting the burst, Sender issues GroupACK Request Control frame
Receiver immediately responds with a Group ACK or an ACK
The ACK lets him mark time until he’s done preparing a real Group ACK
Needs less time to process Group ACK Req, correlate with his Rx buffer
Real Group ACK ready, receiver QSTA transmits it as soon as possible
Sender needs to ACK this Group ACK
Sender can then initiate another burst at his convenience

5. Proposed Group ACK Modifications Summary
January 2003
Proposed Group ACK Modifications Summary
The modified GA remains a relatively involved protocol, but now allows non-QoS STAs to burst transmissions to each other.
No longer necessary to queue up packets at the sender prior to issuing a burst
Better supports pseudo-streaming apps like MPEG2 MPTS distribution to multiple SPTS-processing STBs
Reduced complexity sent/received/need-retransmit packet processing
The herein modified Group ACK is a more robust solution
Candidate normative text revisions to e-D4.0 are contained in document 03/052r0