Downstream network lag is lag where your FPS is fine, but your characters walk jerkily, effects replay, etc.; it is the most common form of network lag. Upstream network lag is characterized by being able to control your characters well. You may see what's going on ok, but your inputs (keyboard and mouse presses) take a while to have an effect.
If you are unsure if you are experiencing network lag or graphics lag, go to the console (ctrl+f8) and enter
host_drawFPS 1. That will show your framerate at the top right corner of the screen. If it stays steady when you lag, you are experiencing network lag. If it drops significantly, you are experiencing graphics lag.
host_drawFPS 2 can be used to show your ping. Please note that ping in Heroes of Newerth is different from standard ICMP pings and measures the actual latency you get when playing.
Another quite reliable way of determining the presence of network lag is to look at your console (ctrl+f8 or your console.log). K2 (HoN's engine) usually marks when it gets network lag with
long server frame and/or