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[STDS-802-11-TGBN] Regarding I-FCS reception rules

Hi all,

 

This email thread is to initiate offline discussion regarding my contribution 11-25/946 on the reception of I-FCS. CID 2166 in the document was based on the following SP which had no objection:

•            Do you support that a UHR STA may treat a received ICF trigger frame as successful if the CRC check on the intermediate FCS, if present, passes.

 

During the call, the main concerns raised on the proposed text were:

  • User Info fields addressed to UHR STAs should be before the I-FCS field to avail control frame protection.
  • Suggest to stick to the wording of the SP.

 

Based on the points, I propose to modify the CR text as follows:

 

If a UHR STA receives a Trigger frame that is an initial Control frame that contains an intermediate FCS, and the STA performs a CRC check on the intermediate FCS field, then:

  • The STA may treat the frame reception as successful if the CRC check on the intermediate FCS field passes, and the CRC check on the FCS field fails.
  • The STA shall treat the frame reception as successful if the CRC check on the intermediate FCS field passes, and if the CRC check on the FCS field either passes or is not performed.
  • The STA shall treat the frame reception as unsuccessful if the CRC check on the intermediate FCS fails.

 

The parts in cyan are not included in the SP text directly. However the cyan parts are needed in my opinion due to the following reasons:

  • Without the second bullet, a UHR STA (e.g. DPS STA or OBSS STA) can early terminate frame reception (after successful I-FCS reception) and “may” choose to not treat the frame reception as successful. This would allow a mechanism for such STAs to avoid setting NAV based on the ICF. So we need a “shall” condition in some cases as described in the second bullet.
  • The last bullet, as I explained on call, is to highlight that CRC check fail of the I-FCS field should have priority over result of CRC check value of FCS field. There is a non-zero probability that CRC check on FCS passes but I-FCS fails, so the spec should clarify this.

 

Looking forward to comments or feedback on the modified text.

 

Regards,

Vishnu

 

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