In a WLAN iperf3 TCP throughput test, I have the following results:
With exactly the same setting, operation in 802.11ac (3x3) (DFS channel) (TCP Cubic)
30 nodes as server receiving iperf -> around 17Mbits avg per node. 30 nodes as iperf clients to a server -> around 4Mbits avg per node.
Is there any reason for this big difference between upstream and downstream?
They are peer-to-peer connections. The client/server or upstream/downstream concepts are application-layer concepts.
Is there something else in the TCP layer that is preventing the full link capacity from being used?
That's why I do not understand if the 802.11, IP and TCP layers are the "same", why there is such a big difference in the transmission rate.
Are there more collisions? Is that problem not solved with CSMA / CA?
What about ARF? This paper discusses the problem of uplink performance: