Hi Mark,
Sorry, you do not convince me :>(
For me the descriptions are clear but I do admit the formula presents a problem. However, I think that the framers got it wrong and the formula should be
(TSF – TSF0) MOD Interval = Offset
Then everything works.
Graham
From: Mark Rison <m.rison@xxxxxxxxxxx>
Sent: Tuesday, December 6, 2022 5:44 PM
To: G Smith <gsmith@xxxxxxxxxxxxxxxxxxx>; STDS-802-11-TGM@xxxxxxxxxxxxxxxxx
Cc: 'mwentink@xxxxxxxxxxxxxxxx' <mwentink@xxxxxxxxxxxxxxxx>
Subject: RE: 11me/D2.0 CID 3502/3503 (Offset field in TDLS peer PSM)
Thanks, Graham. My responses in blue.
CID 3503 says in relation to 1064.20:
"The Offset field is the time in microseconds between TSF 0 and the start of a first Awake Window.
See 11.2.3.12 (TDLS peer power save mode). " -- doesn't seem compatible with "Awake Windows begin at TSF values that satisfy the equation TSF mod Interval = Offset." at 2390.60
GS –I think the ‘formula’ is misleading, but actually correct and compatible. The “Offset” clearly is only appropriate for the “first Awake Window”. Subsequent Awake windows then occur, spaced at
“Interval”.
I do not think the Offset can be the time of the first AW.
If it were so, then you wouldn't be able to set up TDLS peer PSM
2**32 microseconds == about an hour after the BSS had started.
The formula is simply saying that the regular Awake Windows are spaced at Interval, and the remainder is the Offset (i.e., the Offset is not equal to the Interval, or a multiple of it).
Hence, the two are compatible but the formula, although correct, is maybe a horrible way of describing it. I would suggest the formula is deleted and maybe something along the lines of
“After the first Awake window, subsequent
Awake Windows begin at TSF values that are separated by Interval time.”
and CID 3502 says:
"The Offset field is the time in microseconds between TSF 0 and the start of a first Awake Window.
See 11.2.3.12 (TDLS peer power save mode). " -- but the TSF is 8 octets and the Offset field is only 4 octets
and suggests:
Change the first cited text to "The Offset field is the time in microseconds between intervals specified by the Interval field, starting at TSF 0, and the start
of the Awake Window, in microseconds."
GS – I don’t like this. I do not think that Offset and Interval are related at all. Maybe the confusion is on TSF 0? What exactly is that? It seems to be a TSF value at time zero. So I don’t think
it starts at the beginning of the TSF field, but at the end of it?
I personally would leave this alone.
As discussed above, the Offset cannot be the time of the first AW, because it's too small.
I think it works like this (picking easy numbers):
- Say the Interval is 10000 us, the Offset is 4000 us and the TSF is currently 100500 us (when we decide to do TDLS peer PSM)
- The Interval being 10000 us and the Offset being 4000 us means that we potentially have AWs starting at n * 10000 + 4000, n >= 0
- If the TSF is currently 100500 us then the first AW will start at TSF 104000 us (n = 10), then the next one at 114000 us (n = 11), etc.
Note this satisfies "Awake Windows begin at TSF values that
satisfy the equation TSF mod Interval = Offset." from 2390.60.
Please speak up if you have any questions or comments.
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
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