Networking failure - RC Groups
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This thread is privately moderated by Jack Crossfire, who may elect to delete unwanted replies.
Sep 30, 2012, 02:03 AM
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Networking failure

So the networking came together. All beacons from the laptop to any wireless address have go to the copter, because that's how it just is. Linux can't put in anything except the copter MAC as the destination for every IP address.

Then the copter has to shuffle the addresses in the 802.11 header & forward some packets to the camera. The camera beacons contain servo X & Y. The camera sends picture data in response, to the copter. The copter forwards it again, to the laptop.

The address shuffling is:

                  dst address, src address, filter address 
laptop to copter: copter, laptop, camera
copter to camera: camera, copter, laptop
camera to copter: copter, camera, laptop
copter to laptop: laptop, copter, camera

Miraculously, it works but loses a lot of packets.

There are probably ways to manually override the MAC address on all the wireless cards or get them into promiscuous mode, so anyone can talk directly to anyone. It would require more investment in the driver, sending packets out of order, or using the laptop networking stack in a way which won't work everywhere. Eventually, the copter is supposed to process everything.

This scheme ended up not working very well. Either there are a lot of collisions or the USB bandwidth on the copter isn't high enough to do all the packet forwarding.

The return packets from the camera may conflict with the return packets from the copter. The forwarded beacons double the bandwidth usage, reducing the maximum beacon frequency.

There's no consumer product which has 2 wireless stations communicating in realtime with a single tablet. If it's sending video, it's 1 access point & 1 tablet. If it's a sensor network, it communicates very infrequently.

This is heading back towards a tethered USB device, with hope the tablet has a USB host adaptor.
Last edited by Jack Crossfire; Sep 30, 2012 at 02:09 AM.
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