I have a system that I've built for using optical signals to communicate underwater. I'm using a GNURadio + USRP system to test this and I have a program that creates an ethernet connection across my system. I need to measure the link quality as a function of communication distance, water quality, etc.
My question is what method should I use to measure ethernet link quality, and how? Say I have a FTP connection, how would I go about measuring and plotting the retransmits? Or, is there an easy way to directly measure TCP packet CRC failures? What other useful metrics could I gather? I want something more high-level than bit-error rate vs. signal/noise.