Wi-fi network with multiple UDP flows - only one succeeds in transmission

[phar...@gmail.com]

Hi,

I'm trying to simulate a Wi-Fi network with two Wi-Fi stations connected to an AP with heavy traffic. I want to manually enter a physical data rate for each link and obtain a throughput value for each Wi-Fi connection. To do this I've edited the "vht-wifi-network" script to manually select the physical data rate to use. To simulate heavy traffic on the network I've installed a UDP server on each Wi-Fi station and installed their respective clients on the AP.

The problem is: when I run the script, only the first wireless station receives any data and provides a throughput value > 0 mbps.

I've checked to make sure the ports are different per application and that the client starts after and finishes before the server. I've also checked to make sure the packet interval isn't too short. I've searched the mailing list and the web, re-read the tutorial and I can't identify where/what the problem is in my code.

I'd appreciate some feedback on the attached script on whether I have made a mistake in the setup of the network.

I'm using the most recent version of ns-3 (ns-3.25)

I've attached the script and a pcap file for a trace completed on the AP.

Thanks.

[Konstantinos]

We have discussed this in the past several times and it is mentioned in the tutorial slides, you start all the applications at the same time.
You need to give some randomness in your system. This is primarily due to deterministic timers in ARP.

[Phardaem]

Hi Konstantinos,

I don't think it's the ARP that's the issue in this case (though I could be wrong..). When considering the pcap files before even getting to the point where the applications can send the second wi-fi station is failing to associate to the AP. Looking at the pcap file from the AP, it can't see multiple association request frames that are being sent by the second wi-fi station at the beginning of the simulation. It's strange because the pcap files for the wi-fi stations both see the second station's association requests.

Snapshot of pcap from AP:


Snapshot from second wi-fi station:




I tried changing the wi-fi standard from 11ac to 11n out of curiosity but the same issue was seen.

I've attached the pcap files I'm talking about. 2-0 is the AP, 0-0 is the first wi-fi station and 1-0 is the second wi-fi station that is failing to associate to the network. I edited the original script I shared to only start applications after 30 seconds and to simulate of ronly 0.1 seconds to demonstrate the error (attached).

Either I've made an error in the setup or this is a potential bug?

Thanks,

[Phardaem]

I have identified the issue now. In case this is useful for users in the future, if you use the ConstantSpeedPropagationDelayModel and choose to set your own speed value make sure you use a value that is greater than zero.