[Discuss-gnuradio] How is it possible that I receive a packet from the same USRP that transmitted it?

[Thomas Arcuri]

Hello all,

Currently I am testing a modified version of tunnel.py, but I am seeing some strange results. My modifications were essentially a re-factoring to prepare for future additions, however somehow I was able to receive a transmitted packet on the same USRP that transmitted it.

The USRP transmit/receive paths are set-up exactly the same as in the original tunnel.py, the only difference is that I abstracted the tun/tap layer a bit (in order to improve the MAC layer functionality). I did not change the cs_mac loop and I am only using a single USRP with the modified tunnel to flood PING requests. I am using only a single antenna on a WBX d'board.

I know that I am receiving a transmitted packet because in phy_rx_callback() I am using scapy to dump the packet and inspect its contents. This doesn't happen consistently - I am flooding out PING requests but only a relative few are "looped back" (for lack of a better word).

Now, can anyone explain how this could possibly happen?

Thanks,
Tom