[STDS-802-11-TGM] REVmc comment 7770

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Dear TGmc participants,

I was tasked to generate and circulate a resolution for Comment 7770. This email does this. I propose to bring this resolution

to TGmc for consideration asap.

7770

615.36

9.3.1.20

It says "If the VHT NDP Announcement frame contains only one STA Info field, then the RA field is set to the address of the STA identified by the AID in the STA Info field.", but the AID in the STA Info field cannot identify a STA, if that STA is in fact an AP or a mesh STA or an IBSS STA. Also, there's no AID in the STA Info field

Change to "If the VHT NDP Announcement frame contains only one STA Info field and the frame is directed to a non-AP STA in an infrastructure BSS, then the RA field is set to the address of the STA identified by the AID12 subfield in the STA Info field."

MAC

Context: 615.36

The VHT NDP Announcement frame contains at least one STA Info field. If the VHT NDP Announcement frame contains only one STA Info field, then the RA field is set to the address of the STA identified by the AID in the STA Info field. If the VHT NDP Announcement frame contains more than one STA Info field, then the RA field is set to the broadcast address.

The TA field is set to the address of the STA transmitting the VHT NDP Announcement frame or the

bandwidth signaling TA of the STA transmitting the VHT NDP Announcement frame. In a VHT NDP

Announcement frame transmitted by a VHT STA in a non-HT or non-HT duplicate format and where the

scrambling sequence carries the TXVECTOR parameter CH_BANDWIDTH_IN_NON_HT, the TA field is set to a bandwidth signaling TA.

Discussion;

The change proposed in the comment addresses the specific issue raised.

But it doesn’t address the more general comment that an IBSS or mesh STA cannot generate an AID12 value to go in the STA Info field, and probably a non-AP infrastructure STA can’t either.

So the question is whether it is ever meaningful for an IBSS, mess or non-AP STA to generate a VHT NDP announcement frame. If so, then we might want to fix this. If not, we might want to make this constraint explicit.

I was tasked with stimulating discussion on the reflector. I received only one reply which stated:

In Table 8-18a (.11ac, Table 9-25—STA Info subfields in D5.0), Per STA Info field of NDP Announcement frame is defined for STA in infrastructure BSS, AP, non-AP STA in infrastructure BSS, IBSS, mesh network. 11mc’s VHT beamforming already works in IBSS, mesh and outside BSS contexts.

The resolution could be “If the VHT NDP Announcement frame contains only one STA Info field, then the RA field is set to the address of the STA expected to process the following VHT NDP and prepare the sounding feedback ~~identified by the AID in the STA Info field~~.”

As the response indicates, in the case when the intended recipient is an AP, mesh STA or an IBSS STA, Table 9-25 (616.29) clearly indicates that the AID12 field contains a zero.

The normative behaviour is specified in 1461.61:

A VHT beamformee that is an AP, mesh STA, or STA that is a member of an IBSS, that receives a VHT NDP Announcement frame with the RA matching its MAC address and the AID subfield of the only STA Info field set to 0, and that also receives a VHT NDP a SIFS after the VHT NDP Announcement frame shall transmit the PPDU containing its VHT Compressed Beamforming feedback a SIFS after the VHT NDP.

So the only issue is with the cited text. The commenter’s proposed resolution does not work because “STA identified by the AID12 subfield in the STA Info field” does not work when the AID12 field is zero.

The email correspondent’s resolution is better, but contains the problematical “expected”, which generally causes comments of the form “expected by whom”?

The proposed change is as follows: 615.36

The VHT NDP Announcement frame contains at least one STA Info field. If the VHT NDP Announcement frame contains only one STA Info field, then the RA field is set to the address of the STA that can provide feedback (see 10.34.5.2).~~identified by the AID in the STA Info field~~. If the VHT NDP Announcement frame contains more than one STA Info field, then the RA field is set to the broadcast address.

Proposed resolution: Revised.

At 615.38 change “identified by the AID in the STA Info field” to “that can provide feedback (see 10.34.5.2)”.

Best Regards,

Adrian P STEPHENS

Tel: +44 (1793) 404825 (office)
Tel: +1 (971) 330 6025 (mobile)

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