Created attachment 3115 [details]
WiFi network scenario with stations transmitting to AP

Overview: In a Wi-Fi scenario with a large number of 802.11 stations transmitting to an AP under saturation conditions, some stations become blocked and do not transmit. 

Steps to Reproduce:  Run the attached code with the following (default) parameters:
./waf --run "scratch/blocked-sta --simulationTime=30 --nSta=128 --dataRate=0.5Mbps --RngRun=1"

Actual Results: The flows from several stations (e.g., 1, 25, 35) to the AP have zero received packets.

Expected Results: All flows should have some received packets.

Build Date & Hardware: ns-3-dev (changeset 13656:f85ec657c4b0) on Ubuntu 16.04.3

Additional Builds and Platforms:  Doesn't occur on ns-3.28 on Ubuntu 16.04.3

Additional Information: The following methods to fix this problem were tried and did not work:

- increasing the simulation time (also, stopping the transmission from non-blocked stations in the middle of the simulation does not affect the blocked stations),
- changing RngRun (other stations become blocked),
- disabling aggregation (in relation to Bug 2470),  
- using lower MCS values,
- changing to 802.11a,
- starting flows at different times,
- populating ARP cache prior to simulation start.