Install nethogs. It’s somewhat like top or nettop.
sudo apt-get install nethogs
Keyboard shortcuts while you are in the nethogs interface.
m : Cycle between display modes (kb/s, kb, b, mb)
r : Sort by received.
s : Sort by sent.
q : Quit and return to the shell prompt.
Command line options:
-d delay for refresh rate.
-h display available commands usage.
-p sniff in promiscious mode (not recommended).
-V prints Version info.
For osx, you can use the built-in Activity Monitor and head over to the Network tab.