1. Max Frame Length Changes
Month Year
doc.: IEEE yy/xxxxr0
Max Frame Length Changes
Date:
Authors:
Yong Liu, Marvell
John Doe, Some Company

2. Contents Max management frame length change
Max MPDU length in VHT Capabilities element
A-MPDU length limit
Yong Liu, Marvell

3. Max management frame length (1)
In REVmb_D6, the max management frame body length is limited to 2324 octets
Based on the max MSDU size 2304 octets
In 11ac, longer management frame is desired to carry VHT/MU beamforming reports, esp. when Nr > 4 and/or channel BW > 80MHz
Otherwise, beamforming report segmentation is required
The management frame body is not an MSDU, thus need not be limited by the max MSDU size
Yong Liu, Marvell

4. Max management frame length (2)
Max MPDU = octets
Octets: 2 2 6 4
Frame Control
Duration
Address 1 (DA) SA
BSSID
Sequence Control
HT/VHT Control
Frame Body
FCS
Proposal:
If a management MPDU is sent using a VHT PPDU, the length of the MPDU is constrained by the maximum MPDU length supported by the recipient
The Max Frame Body Length can be up to:
11422 octets = – 28 (MAC header) – 4 (FCS) octets
VHT STAs supporting larger management frames need not segment beamforming reports for most cases
If a management MPDU is not sent using a VHT PPDU, the maximum management MPDU size is 2356 octets (still limited by the max Frame Body length 2324 octets)
Yong Liu, Marvell

5. Max MSDU/A-MSDU Length
In REVmb_D6:
8.2.3 General frame format
The Frame Body field is of variable size. The maximum frame body size is determined by the maximum MSDU size (2304 octets) or the maximum A-MSDU size (3839 or 7935 octets, depending upon the STA’s capability),(11n) plus any overhead from security encapsulation.(#2211)
Frame body: 7955 = 7935 (max A-MSDU) + 20 (TKIP overhead)
Note that here max MSDU/A-MSDU lengths are fixed, while max MPDU length is variable
Yong Liu, Marvell

6. Max MPDU Length (1)
Max MPDU = octets
In 11ac, the max MPDU length is fixed (11454 octets), while the max A-MSDU size can be variable
Max A-MSDU length = Max MPDU length (11454) – MAC header length (36) – CCMP overhead (16) – FCS (4) = octets
11414 octets Frame Body should count in the security overhead
It is clearer to define the max supported MPDU length capability
The max supported MPDU length can be used to calculated the max length of the management frame body
Yong Liu, Marvell

7. Max MPDU Length (2) Proposal
Replace the max A-MSDU length subfield in the VHT Capabilities element with a max MPDU length subfield
If a VHT STA does not support octet max MPDU length, it shall set the max VHT MPDU length in the VHT Capabilities element consistent with the max A-MSDU length in the HT capabilities element
Yong Liu, Marvell

8. MU-MIMO paired STAs with different A-MDPU length limit
Month Year
October 2010
r0 LG Link Adaptation for MU-MIMO
doc.: IEEE yy/xxxxr0
MU-MIMO paired STAs with different A-MDPU length limit
802.11n A-MPDU length limit:
If the A-MPDU includes any padding delimiters (i.e., delimiters with the Length field set to 0) in order to meet the MPDU start spacing requirement, this padding is included in this length limit.
Case study:
STA1’s A-MPDU length limit is shorter than STA2’s A-MDPU length limit.
EOF is counted in A-MPDU length limit.
AP has to limit A-MPDU for STA2.
STAs with long A-MPDU length limit have to wait for the next A-MPDU transmission.
Data field for STA#1
EOF
EOF
STA#1
Data field for STA#2
Remained data to transmit.
STA#2
STA2’s A-MPDU length limit.
MU-MIMO Tx to
STA#1 and STA#2
STA1’s A-MPDU length limit.
Because of STA1’s A-MPDU length limit,
AP can transmit until the STA1’s A-MDPU length limit.
STA1’s A-MPDU length limit.
Slide 8
Byeongwoo Kang, LG Electronics
Yong Liu, Marvell
Page 8
Kyoungyoung Song, LGE
John Doe, Some Company

9. Proposal Adding the following text in the specification: Result
Month Year
October 2010
r0 LG Link Adaptation for MU-MIMO
doc.: IEEE yy/xxxxr0
Proposal
Adding the following text in the specification:
“In case of null padding with EOF, the AP will not count the padding delimiters for the length limit.”
Result
STA1’s A-MPDU length limit is shorter than STA2’s A-MDPU length limit.
EOF is not counted in A-MDPU length limit.
AP does not have to limit STA2’s A-MDPU.
Data field for STA#1
EOF
EOF
EOF
EOF
STA#1
Data field for STA#2
STA#2
STA2’s A-MPDU length limit.
MU-MIMO Tx to
STA#1 and STA#2
STA1’s A-MPDU length limit.
Slide 9
Byeongwoo Kang, LG Electronics
Yong Liu, Marvell
Page 9
Kyoungyoung Song, LGE
John Doe, Some Company

10. Pre-motion 1
Should the spec framework document be updated to define the Max VHT Management Frame Length as following?
If a management MPDU is sent using a VHT PPDU, the length of the MPDU is constrained by the maximum MPDU length supported by the recipient
The Max VHT Management Frame Body Length can be up to:
11422 octets = – 28 (MAC header) – 4 (FCS) octets
Yes No
Abstain
Yong Liu, Marvell

11. Pre-motion 2
Should the spec framework document be updated to replace the Maximum A-MSDU Length subfield in the VHT Capabilities element with the max MPDU length subfield
Set to 0 for 3895 octets (Maximum A-MSDU Lenth in HT Capabilities set to 3839 octets)
Set to 1 for 7991 octets (Maximum A-MSDU Length in HT Capabilities set to 7935 octets)
Set to 2 for octets (Maximum A-MSDU Length in HT Capabilities set to 7935 octets)
The value 3 is reserved
Yes No
Abstain
Yong Liu, Marvell

12. Pre-motion 3
Should the spec framework document be updated with the following rule:
In case of null padding with EOF, the transmitter shall not count the padding delimiters for the A-MPDU length limit
Yes No
Abstain
Yong Liu, Marvell