Network activity monitor

[rikona]

I'm having some ongoing issues with Comcast. I'd like to be able to
monitor network speed/activity [just on one Ubuntu box, not the entire
local net] on a continuous, moment-by-moment basis, and a log to
remember start/stop times might be nice but not necessary. Graphical,
like htop, would be preferred but not essential as long as it is
continuous. What is the best tool to do that?

Thanks,

rikona