1. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 1 Max Frame Sizes Date: 2010-09-13 Authors:

2. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 2 Contents 802.11n max frame sizes Larger MPDU/A-MPDU support –Motivations –CRC-32 characteristics –MAC efficiency calculations 802.11ac max frame sizes Conclusions

3. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 3 802.11n max frame sizes Max MSDU: 2,304 B Max A-MSDU: 3,839 B or 7,935 B –HT Capabilities element → HT Capabilities Info field → Maximum A- MSDU Length subfield (0: 3,839 B, 1: 7,935 B) Max Frame body of CCMP MPDU:7919 B –7919 B = 7935 B – 8B MIC – 8B CCMP header Max MPDU in A-MPDU: 4,095 B –Limited by 12-bit MPDU Length field in MPDU delimiter Max A-MPDU in HT-PPDU: 8,191B ~ 65,535 B –Limited by 16-bit HT Length field in HT-SIG –HT Capabilities element → A-MPDU Parameters field → Maximum A- MPDU Length Exponent: (2 13 -1) B ~ (2 16 -1) B

4. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 4 Larger MPDU/A-MPDU support Motivations –Wider bandwidth (80/160MHz) => higher PHY data rate => shorter PHY payload duration => higher preamble overhead –The max VHT PPDU/A-MPDU duration is limited by the max number of symbols indicated by L-SIG length, which is 1365 * 4us = 5.46 ms (around 666KB @ 1Gbps, and 1.3MB @ 2Gbps) –3 reserved bits remain in MPDU delimiter, which can be used to extend the max MPDU length

5. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 5 CRC-32 error checking characteristics The error checking mechanism of CRC-32 was characterized by R. Jain, "Error Characteristics of Fiber Distributed Data Interface (FDDI)," IEEE Transactions on Communications, Vol. 38, No. 8, August 1990, pp. 1244-1252 FDDI, Ethernet, and 802.11 use the same CRC-32 error checking mechanism The probability of undetected errors remains constant for frame sizes between 3007 and 91639 bits –91639b = 91607b data + 32b CRC

6. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 6 MAC Efficiency Calculations (1) Parameters –AIFS: 34us –Average CW: 67.5us –MSDU: 1500B –Max MPDU (~ Max A-MSDU) 1540B (w/o A-MSDU) 4095B (w/ A-MSDU) 8197B (w/ A-MSDU) 12287B (w/ A-MSDU) 16383B (w/ A-MSDU) –Max BA window: 32 –BA: legacy rate –TXOP duration: 3ms TXOP truncation enabled –Note: actual A-MSDU/MPDU and A-MPDU sizes depend on TXOP duration and residual TXOP duration

7. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 7 MAC Efficiency Calculations (2)

8. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 8 MAC Efficiency Calculations (3)

9. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 9 MAC Efficiency Calculations (4)

10. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 10 MAC Efficiency Calculations (5)

11. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 11 Max MPDU size Max MPDU size is increased to 11454B –11454B = 11450B (~91607b) + 4B FCS –Maintain the same CRC-32 error checking characteristics –Improve MAC efficiency for very high data rate MPDU Length in delimiter is extended to 14 bits

12. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 12 Max A-MSDU and A-MPDU sizes Max A-MSDU –Max A-MSDU = Max MPDU – Max MAC header – FCS –Extend Maximum A-MSDU Length subfield by 1 bit (0: 3,839 B, 1: 7,935 B, 2: {11454 B – Max MAC header – FCS}, 3: reserved) –Max Frame body of CCMP MPDU = Max A-MSDU – 8B MIC – 8B CCMP header Max A-MPDU –If the max BA window is maintained to 64, the max A-MPDU can be up to 733,056B –Extend Maximum A-MPDU Length Exponent subfield by 1 bit: 0-7 => (2 13 -1) B (=8191B) ~ (2 13+7 -1) B (=1MB -1)

13. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 13 Conclusions Propose to extend max MPDU, max A-MSDU, and max A-MPDU sizes to improve MAC efficiency Define max MPDU, max A-MSDU, and max A-MPDU sizes for 11ac Extend the 802.11n max frame size negotiation/signaling to support new max frame sizes

14. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 14 Reference 11-10-yyyy-00-00ac-a-mpdu-delimiter-changes.ppt

15. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 15 Straw Poll 1 Should the spec framework document be updated to include the following limits: –Max MPDU = 11454B –Max A-MSDU = 11454B – Max MAC Header - FCS –Max A-MPDU = 1MB –Yes: –No: –Abstain:

16. doc.:IEEE 802.11-10/1079r0 Submission Sept. 13, 2010 Yong Liu, MarvellSlide 16 Straw Poll 2 Should the spec framework document be updated to include the following capability signaling: –Max A-MPDU length supported as exponent n where 0 <= n <=7 and indicates a max A-MPDU length (2^(13+n)-1)B –Max A-MSDU length supported as 3839B, 7935B or {11454B- Max MAC Header-FCS} –Yes: –No: –Abstain: