I'm not sure where the gap in milliseconds is coming from. EDCA gaps are mostly driven by probabilities. If energy detect (ED) indicates the medium is available then the gap prior to transmit, assuming no others competing & winning at that moment in time, is driven by AIFS and the CWMIN - CWMAX back offs which are simple probability distributions. Things change a bit with 802.11ax and trigger frames but the gap is still determined by the backoff and should be less than milliseconds per that. Things like NAVs will impact the gap too but that happens when another is transmitting.
 

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Agreed that the PLCP preamble is at low MCS and the payload can be orders of magnitude greater (per different QAM encodings and other signal processing techniques.)

Bob

On Wed, Oct 19, 2022 at 12:09 AM David Lang <david@lang.hm> wrote:
On Tue, 18 Oct 2022, Sebastian Moeller wrote:
> Hi Bob,
>
>> Many network engineers typically, though incorrectly, perceive a transmit
>> unit as one ethernet packet. With WiFi it's one Mu transmission or one Su
>> transmission, with aggregation(s), which is a lot more than one ethernet
>> packet but it depends on things like MCS, spatial stream powers, Mu peers,
>> etc. and is variable. Some data center designs have optimized the
>> forwarding plane for flow completion times so their equivalent transmit
>> unit is a mouse flow.
>
> [SM] Is this driven more by the need to aggregate packets to amortize some cost over a larger payload or to reduce the scheduling overhead or to regularize things (as in fixed size DTUs used in DSL with G.INP retransmissions)?

it's to amortize costs over a larger payload.

the gap between transmissions is in ms, and the transmission header is
transmitted at a slow data rate (both for backwards compatibility with older
equipment that doesn't know about the higher data rate modulations)

For a long time, the transmission header was transmitted at 1Mb (which is still
the default in most equipment), but there is now an option to no longer support
802.11b equipment, which raises the header transmission time to 11Mb.

These factors are so imbalanced compared to the top data rates available that
you need to transmit several MB of data to have actual data use 50% of the
airtime.

David Lang

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