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| --- This message came from the IEEE 802.11 Working Group Reflector ---
Hello, This discussion seems to have gone quiet, and I'm wondering whether it's just that it's going on in a place I'm not aware of. I think that many/most people would agree that if we could save 6 octets per MSDU by switching from LPD to EPD, that would in principle be desirable. The concerns are about backward-compatibility (on the assumption a 5G9 device might have to roam to or otherwise support other bands in some situations). It seems to me that we can use EPD with backward-compatibility as long as we take some precautions: - Have an extended capabilities bit to say "I understand EPD". Do not use EPD to STAs which don't say they understand it (this means all the STAs, in the case of group-addressed transmissions by an AP; note that there would be the complexity that an AP receiving an EPD frame from a STA which is to be broadcast back would have to convert it to LPD if any STAs didn't understand EPD) - Signal the use of EPD through some mechanism, e.g. use of the remaining unused Data frame subtype (1101), or if PCF/HCCA needs to be supported, a triplet or quartet of Extension frame subtypes (depending on whether the non-+CF subtype remains as a Data frame for simplicity with devices which don't care about PCF/HCCA). A similar technique can be used for the "PV1" frames with a compressed MAC header introduced by 11ah (there are enough reserved Types) [I am assuming no-one cares about non-QoS STAs enough anymore to worry about supporting EPD with them.] There are other possibilities, such as these, but they seem more hacky to me: - Special-case the Ethertypes AA-AA (and maybe also E0-E0 and FF-FF per Tables P-2 and P-3 in P802.11 REVmc/D4.0), saying that if the MSDU starts with this it's actually LPD, but otherwise it's EPD (this means that in the worst case, if Ethertypes AA-AA, E0-E0 and FF-FF had to be supported, they would have to be used with LPD) - Have prior agreement on use of EPD, e.g. specified in a relevant standard (such as DSRC/ITS/11p or 11ah; but as described above there were concerns about this approach), or dynamically signalled, e.g. via the Extended Capabilities element in Management frames exchanged before any Data frames (such as in (Re)Association Request/Response frames in an infrastructure BSS) - Find some other MAC header bit to signal use of EPD Any thoughts? Think of all those octet sextuples we could save! 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: *** IEEE stds-802-11 List *** [mailto:STDS-802-11@xxxxxxxx]
On Behalf Of Hamilton, Mark --- This message came from the IEEE 802.11 Working Group Reflector ---
All, I have requested that Adrian add this topic to the mid-week plenary agenda:
EPD (EtherType) format for MSDUs for OCB/ITS communications in the 5.9GHz band. Material can be found here:
https://mentor.ieee.org/802.11/dcn/14/11-14-1521-04-000m-epd-for-ieee802-11-5-9ghz-operations.pptx
I will be asking the WG for a Straw Poll, and likely a Motion, to gauge the support for this proposal before requesting it be considered by TGmc. Please review the materials ahead of the mid-week plenary, if possible, and be prepared to indicate whether you can support the proposal. Also, please let me know if you have any questions, of course. Mark Hamilton _______________________________________________________________________________
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