Problem with Dropped Packets via Wireless Monitor Mode


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Sep 26, 2020
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Hello All,
I am trying up a fast data transmission channel via wireless USB devices.
My transmission side is an RPI 4 and my receiving side is a Desktop.

I am setting both usb wifi cards in monitor mode at 5.8 GHz frequency. I am using a program that creates a UDP connection and sends packets as fast as possible.

The problem is that the maximum bitrate I can achieve without dropping packets is about 4 Mbps.
I believe I discarded software problems and the usb wifi problems because when I plug in both usb wifi cards on my desktop and run the same software, I achieve a bitrate of about 26 Mbps.

Does anybody know about any inherent limitations of RPIs regarding networking? Do you believe it is a bottleneck on the CPU, or it is not efficient to run a fast data network channel through its USB ports?

The previous RPi had USB constraints, but the 4 did away with those constraints and now heads into the system on a PCIe channel. So, it's unlikely to be the USB. If it is an RPi < 4, then USB would be where I'd first check.

Lemme dig out a citation...

That should sum it up.

My *guess* would be that it's one of two things. It's CPU limited - or it's a driver issue with the specific distro you have on the Pi. If the distro is the same on both, that'll eliminate that issue. It could be an older driver, there could be some bug in implementation, etc...

But, without knowing anything more, I'd lean towards the CPU being where you're bottlenecked.

Even though your device *is* technically working, I'd take a look at the troubleshooting steps at the bottom of the linked page. Checking through the logs reveal some useful information.

You can also run 'top' while you're doing this data transfer and check on the CPU usage to see if it's abnormally high. There is more, but I'd start there.
Thanks for the reply and help.
I ended up trying a few different things with the drivers, code, and different computers.

I came to the conclusion that my implementation is slow. I am not maxing out my CPU in either RPI or my desktop. But obviously my powerful desktop is going to make my inefficient code run fast compared to the RPI. Thanks again

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