I've recently started using the SolarWinds Bandwidth Monitor to keep track of a long standing problem we've been having with our internet connection. Before starting to run this my monitoring has consisted of ping -t on the IP that I believe represents our modem and the IP for the first Time Warner server hop to anywhere. At irregular times of day and for irregular intervals the ping will spike dramatically, we're talking 1-3 seconds and timing out. In order to better monitor what is happening I have tried several bandwidth monitors. I haven't been especially happy with any of them for my very specific needs, but SolarWinds has a very friendly graphical display, or it would be if I had any idea what I was specifically looking at.
I have it monitoring the router. I had the option of eth0 and eth1 which were both showing activity. eth0 shows activty in Traffic Out and eth1 shows activity in Traffic In. They're identical, just opposite. Unfortunately I really don't know what, specifically, it is or is referencing. Since they show the same information, just flipped I chose to only monitor eth0.
During normal activity Traffic In hangs out very close to 0 bps. Traffic Out is always above Traffic In, running a jagged line that peaks around 1.3 or 1.4 Mbps. On my command prompt ping -ts this comes out as a consistently flow of 9-15ms to both IPs. During a spike Traffic In jumps to 1.1-1.3 Mbps and Traffic Out drops down below that to close to 0 consistently without any, or only occasional, spikes. Again, I don't know what it means, but it happens every time the ping times out.