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Doc.: IEEE 802.11-10/1093r0 SubmissionRobert Stacey, Intel A-MPDU Delimiter Changes Date: 2010-09-12 Authors: Slide 1 September 2010.

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Presentation on theme: "Doc.: IEEE 802.11-10/1093r0 SubmissionRobert Stacey, Intel A-MPDU Delimiter Changes Date: 2010-09-12 Authors: Slide 1 September 2010."— Presentation transcript:

1 doc.: IEEE /1093r0 SubmissionRobert Stacey, Intel A-MPDU Delimiter Changes Date: Authors: Slide 1 September 2010

2 doc.: IEEE /1093r0 Submission Increase Length field to accommodate longer MPDU Support ACK response to QoS Data frame A-MPDU Delimiter Changes September 2010 Robert Stacey, IntelSlide 2

3 doc.: IEEE /1093r0 Submission The Length field in current A-MPDU delimiter is 12 bits –Supports a 4KB MPDU At VHT data rates, we need to support larger MPDUs to maintain same MAC efficiency –Up to 12KB MPDU is needed to maintain efficiency with 64 MSDU BA window limit Increase Length field September 2010 Robert Stacey, IntelSlide 3

4 doc.: IEEE /1093r0 Submission Marvell Slide 4 MAC Efficiency Calculations (1) TXOP Limit = 3ms (w/ truncation), AIFS=34us, Avg CW = 67.5us, MSDU 1500B, BA buffer limit = 32

5 doc.: IEEE /1093r0 Submission Marvell Slide 5 MAC Efficiency Calculations (2) TXOP Limit = 3ms (w/ truncation), AIFS=34us, Avg CW = 67.5us, MSDU 1500B, BA buffer limit = 32

6 doc.: IEEE /1093r0 Submission B0B1B2 B3B4 B15B16 B23 B24 B31 EOFReservedMPDU Length Extension MPDU LengthCRCDelimiter Signature A-MPDU Delimiter format September 2010 Robert Stacey, IntelSlide 6 Length extension occupies 2 reserved bits and contains high order length bits Note – all fields are LSB first so LSB of length is in B4, LSB of length extension is in B2 EOF (already in spec framework) occupies a currently reserved bit

7 doc.: IEEE /1093r0 Submission VHT frame format always contains A-MPDU and has no Aggregate bit 11n has a protocol rule: –If Aggregate = 0 and QoS Control Ack Policy = normal ack Respond with ACK –If Aggregate = 1 and QoS Control Ack Policy = normal ack Respond with BA We need a signaling mechanism in 11ac that supports the same protocol rule –Maintain a common protocol engine between 11n and 11ac –Support a slightly more efficient protocol at low MCS –Support QoS data transfer without BA agreement Support ACK response to QoS Data September 2010 Robert Stacey, IntelSlide 7

8 doc.: IEEE /1093r0 Submission Mbps (1x1, 80 MHz, BPSKr1/2) Includes contention overhead and 10% PER Using ACK instead of BA provides a small efficiency increase –Between 1% and 3% –Slightly more if we consider TCP traffic with 40B ack packets MAC efficiency with ACK vs BA September 2010 Robert Stacey, IntelSlide B Data ACK BA 5 x 1500B Data (A-MSDU) ACK BA 44us 68us 2.1ms 440us MAC efficiency = 61.0% MAC efficiency = 58.7% MAC efficiency = 80.2% MAC efficiency = 81.1%

9 doc.: IEEE /1093r0 Submission After association, there is a management exchange to establish the BA session Without BA agreement, initiator cannot send data using VHT frames –Initiator would need buffer traffic until BA session was established –Or initiator would need to use HT/11a format packets Both options require change from 11n –In 11n you simple send non-aggregate packets until BA session is in place Data transfer before BA agreement is in place September 2010 Robert Stacey, IntelSlide 9

10 doc.: IEEE /1093r0 Submission Even with BA agreement in place, it is useful to do a Data/ACK exchange –As a collision detect mechanism at start of a long TXOP –When you only have a single MPDU to send and all previous MPDUs have been acknowledged Data transfer with BA agreement September 2010 Robert Stacey, IntelSlide 10 Data ACK Data/Data/Data/Data (A-MPDU) BA

11 doc.: IEEE /1093r0 Submission Options for Single MPDU signaling: –VHT-SIG-A –SIGNAL field –A-MPDU delimiter We prefer signaling in A-MPDU delimiter: –Purely a MAC function: affects protocol only –Different from 11n where Aggregate bit had two functions: defined frame format and protocol Why signal in A-MPDU delimiter? September 2010 Robert Stacey, IntelSlide 11 PHY MAC

12 doc.: IEEE /1093r0 Submission Use EOF bit for Single MPDU signaling September 2010 Robert Stacey, IntelSlide 12 Delimiter MPDU Alignment PadDelimiter MPDU Alignment PadDelimiter MAC EOF Pad A-MPDU Delimiter MPDU Alignment PadDelimiter MAC EOF Pad A-MPDU Delimiter with EOF=1, length>0 single MPDU frame EOF=0, length>0EOF=0, length=0EOF=1, length=0 EOF=1, length>0 Multi-MPDU frame Single MPDU Delimiter

13 doc.: IEEE /1093r0 Submission If an A-MPDU contains a single MPDU, the initiator may set the EOF field in the A-MPDU subframe containing the MPDU to 1 A responder that receives a QoS Data MPDU with ack policy set to normal ack/implicit block ack shall respond: –With ACK if the EOF field of the subframe containing the MPDU is set to 1 –With BA if the EOF field of the subframe containing the MPDU is set to 0 An initiator may send a management frame in a VHT frame provided it is the only MPDU in the VHT frame and the EOF field on the subframe carrying the MPDU is set to 1 Single MPDU Protocol Rules September 2010 Robert Stacey, IntelSlide 13

14 doc.: IEEE /1093r0 Submission Do you support updating the spec framework document to show the A-MPDU delimiter format extended from n as described below and including the figure? –An MPDU Length Extension field is added in B2-B3 and contains the high order bits of MPDU length –An EOF field is added in B0 Strawpoll #1 September 2010 Robert Stacey, IntelSlide 14 B0B1B2 B3B4 B15B16 B23 B24 B31 EOFReservedMPDU Length Extension MPDU LengthCRCDelimiter Signature

15 doc.: IEEE /1093r0 Submission Do you support updating the spec framework document to include the Single MPDU protocol rules on slide 13? Strawpoll #2 September 2010 Robert Stacey, IntelSlide 15


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