March 2011 doc.: IEEE 802.11-11/0396r0
IEEE P802.11
Wireless LANs
Date: 2011-03-14
Author(s):
Name / Affiliation / Address / Phone / email
Robert Stacey / Intel Corporation / 2111 NE 25th Ave, Hillsboro, OR 97124 / +1-503-724-0893 /
Comments
1118 / Stacey, Robert / 7.1.2 / 4 / 14 / TR / The maximum MPDU size supported by the recipient may also limit the Frame Body size. Also, the maximum A-MSDU size applies to HT STAs and is limited to 2 values (3835 and 7935) not 3. / Change to read: "The PPDU in which the frame is transmitted, the maximum MSDU size (2304 octets), the maximum A-MSDU size supported by a HT STA recipient (3839 or 7935) or the maximum MPDU size supported by a VHT STA recipient (3895, 7991 or 11454) may further limit the maximum MPDU size."1119 / Stacey, Robert / 7.1.2 / 4 / 27 / TR / A maximum frame body size of 11424B is possible in a QoS Data frame withput HT Control or Address 4. A maximum frame body size of 11426B is possible in a management frame. / Correct the figure to show Frame body size range of 0-11426. Replace the note with one that states how this number is arrived at: management frame without HT control.
1122 / Stacey, Robert / 7.2.3.0a / 10 / 58 / TR / By my calculation, the maximum Frame Body size in a management frame is 11426 (not 11422) since the frame may not include the HT Control field. / Change 11422 to 11426. An argument could be made that the Frame Body should be limited to 11422 since the frame may dynamically include HT Control based on lower MAC operation (e.g. link adaptation) and you wouldn’t want that to impact upper MAC functionality. However, this is an implementation consideration and the implementer could constrain the upper MAC implementation to always use the smaller size if there is a possibility that the lower MAC will dynamically insert HT Control.
Discussion
The field ranges in the figures for the General frame format and Management frame format do not reflect the actual ranges that are possible given by the normative requirements. VHT frames are limited by the maximum MPDU size indicated in the VHT Capababilities element with the largest MPDU size being 11545B.
For a management frame this means the Frame Body field is in the range 0 to 11454 less the smallest MAC header less FCS. This works out to 0-11426. This range should appear in the general frame format and in the Management frame format.
For a Data frame the Frame Body rage is 0 to 11454 less the smallest QoS Data MAC header less FCS. (QoS Data MAC header and not Data MAC header since only QoS Data frames are permitted in an A-MPDU and VHT frames always use A-MPDU). The smallest QoS Data MAC header is 26 octets (Full MAC header less Address 4 less HT Control) This results in a Frame Body field range of 0 to 11424 (11545-26-4). This range should appear in Figure 8-27.
In my suggested resolution for CID #1119, I said modify the note to describe where the number comes from. I think we could just delete the note.
Resolution
Changes based on P802.11ac/D0.2.
8.2.3 General frame format
Change the first paragraph as follows:
The Frame Body field is of variable size, but constrained by the maximum MPDU size of 11,454 octets. The PPDU duration in which the frame is transmitted, the maximum MSDU size (2304 octets) and, the maximum A-MSDU size supported by thean HT STA recipient (3839, or 7935 or 11,398 octets) or the maximum MPDU size supported by a VHT STA recipient (3895, 7991 or 11545)may further limit the maximum MPDU size. The maximum frame body size is determined by the maximum MSDU size (2304 octets) or the maximum AMSDU size (3839 or 7935 octets, depending upon the STA’s capability), plus any overhead from security encapsulation.
Change Figure 8-1 to show a Frame Body size range of 0-11426.
Delete the note following Figure 8-1.
8.3.2 Data frames
8.3.2.1 Data frame format
Insert Figure 8-27 from REVmb 7.0 and modify to show a Frame Body range of 0-11424.
8.3.3 Management frames
8.3.3.1 Format of Management frames
Chage Figure 8-30 to show a Frame Body size range of 0-11426.
Submission page 3 Robert Stacey, Intel