track nw d/l speeds?

[d.adams]

Hello: I use wise system monitor to track performance, loads at boot. I saw that for some minutes something was giving download speeds of up to 1.5 M/s (presumed they mean megabits/sec). Is there a way to view what exactly is being sent to my pc while this so-called download is happening? I believe autoupdate of my security sw was long since done for the day. I had closed both my email & browser, to see if this reduced the speed. This did reduce to about 500K/s, mostly. Now it is at 0 K/s w/email & browser opened (presumed not active or in cache mode?). Thanks.