I think that in general (a) the STA knows approximately when the last
Beacon frame was transmitted (from the TSF) and (b) high precision is
not necessary as the time delta will typically be several beacon
intervals. Therefore I think the current Switch Time field description
would be sufficient. We could change it to say something like
"between the time the CSA frame is transmitted by the AP and the expected time of the first Beacon frame in the new channel"
for the count=0 case but I think this would be unnecessary extra work
for the AP.
See my other post as to the benefit to the STA, even if there is an
error of a few TUs in the delta.
Thanks,
Mark
--
Mark RISON, Standards Architect, WLAN English/Esperanto/Français
Samsung Cambridge Solution Centre Tel: +44 1223 434600
Innovation Park, Cambridge CB4 0DS Fax: +44 1223 434601
ROYAUME UNI WWW: http://www.samsung.com/uk
From: Yongho Seok <yongho.seok@xxxxxxxxx>
Sent: Monday, 29 August 2022 18:22
To: STDS-802-11@xxxxxxxxxxxxxxxxx
Subject: Re: [STDS-802-11] Channel Switch Count question/suggested change in REVme
--- This message came from the IEEE 802.11 Working Group Reflector ---
Hi Mark,
In the Max Channel Switch Time element, the offset of the Switch Time field is based on the time the last Beacon frame is transmitted.
"The Switch Time field is a 3-octet field indicating the maximum time delta between the time the last Beacon frame is transmitted by the AP in the current channel and the expected time of the first Beacon frame in the new channel, expressed in TUs."
However, if the Channel Switch Count field is set to 0, the STA can't determine the offset of the Switch Time field in the Max Channel Switch Time element because the STA can't determine the time the last Beacon frame is transmitted by the AP.
"For nonmesh STAs, the Channel Switch Count field is set to the number of TBTTs until the STA sending the Channel Switch Announcement element switches to the new channel. The value 1 indicates that the switch occurs at the next TBTT (the ensuing Beacon frame is created assuming the new channel), and the value 0 indicates that the switch occurs at any time after the frame containing the element is transmitted."
FYI, for non-zero Channel Switch Count field value, the STA can determine the offset of the Switch Time field in the Max Channel Switch Time element according to the definition (that provides the number of TBTTs until the last Beacon frame).
If we remove "When the AP sets the Channel Switch Count field of the Channel Switch Announcement element to 0, it shall not include a Max Channel Switch Time element in a Beacon or Probe Response frame.", another question should be clarified. How can the Max Channel Switch Time element have the benefit even when the offset of the Switch Time field is unknown? Probably, we should not remove this sentence.
Thanks,
Yongho
2022년 8월 27일 (토) 오후 12:50, Mark Hamilton <mark.hamilton2152@xxxxxxxxx>님이 작성:
--- This message came from the IEEE 802.11 Working Group Reflector ---
All,
I’m looking for those interested in Channel Switch Announcement procedures, to consider a change being proposed in REVme (see below).
Does anyone have a comment/concern with this proposed change?
Thanks. Mark
1812
Mark RISON
2799.35
11.8.8.2
"When the AP sets the Channel Switch Count field of the Channel Switch Announcement element to 0, it shall
not include a Max Channel Switch Time element in a Beacon or Probe Response frame(#6)." -- why not? Even if you have to switch immediately, the AP might not be available on the new channel for a whileDelete the cited text
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