[Starlink] SatNetLab: A call to arms for the next global> Internet testbed

[Ben Greear]

On 7/13/21 11:01 AM, David Lang wrote:
> On Tue, 13 Jul 2021, Rodney W. Grimes wrote:
> 
>> It wasnt suggested "lowering the bit rate", it was suggested to make the
>> packets smaller, which actually does address the hidden transmitter problem
>> to some degree as it *would* reduce your air time occupancy, but the damn
>> wifi LL aggregation gets in your way cause it blows them back up.  When I
>> am having to deal/use wifi in a hidden transmitter prone situation I always
>> crank down the Fragmentation Threshold setting from the default of 2346 bytes
>> to the often the minimum of 256 with good results.
> 
> The problem is that with wifi at modern data rates, you have a header at a low data rate and then data at a much higher data rate (in extreme cases, a >50x 
> difference), so the amount of data that you send has a pretty minor difference in the airtime used. So you really do want to send a large amount of data per 
> transmission to minimize the overhead
> 
> IT's not quite as bad if you have disabled 802.11b speeds on the entire network as that raises the header/housekeeping transmissions from 1Mb/s to 11Mb/s

The quiesce period waiting for medium access also takes some time, so that is another reason to try to put lots of
frames on air in the same tx operation...

David, I'm curious about the rate-ctrl aspect of this.  Have you found any implementations of rate-ctrl
that try harder to decrease amsdu groupings and/or keep MCS higher (maybe based on RSSI?) in a congested
environment to deal better with hidden node problems?

Thanks,
Ben

-- 
Ben Greear <greearb at candelatech.com>
Candela Technologies Inc  http://www.candelatech.com