Just scroll down on the pages you linked to. The posts and many other OFDMA related posts are there.

I also recommend this blog https://gjermundraaen.com/

> On Jan 27, 2020, at 8:17 AM, Rich Brown <richb.hanover@gmail.com> wrote:
> 
> 
>>> On Jan 26, 2020, at 12:00 PM, make-wifi-fast-request@lists.bufferbloat.net wrote:
>>> 
>>> An ongoing issue is that I'm not sure what I'm supposed to be seeing
>>> when sniffing OFDMA DL and UL traffic. The DL OFDMA and UL OFDMA
>>> sequences described in David Coleman's Aerohive blog posts, which are
>>> also in the CWNA 5th Edition Study Guide that David co-authored, have
>>> yet to be seen.
>>> https://blog.aerohive.com/dl-ofdma/
>>> https://blog.aerohive.com/uplink-orthogonal-division-multiple-access-ul-ofdma-in-802-11ax/
> 
> Regrettably, these links no longer work. (They vector off to a ExtremeNetworks page.) The original blog.aerohive.com page still exists, though: https://blog.aerohive.com/author/davidcoleman/
> 
> Has anybody found current links to these posts? Thanks.
> _______________________________________________
> Make-wifi-fast mailing list
> Make-wifi-fast@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/make-wifi-fast