"Unlike most bandwidth monitoring tools, which display network usage per IP address or per protocol, NetHogs monitors the network and presents bandwidth usage per application. Thus you can see how much bandwidth the RSS aggregator, browser, software updater, and even IRC and IM clients are using.
"NetHogs is available through the software repositories for most distributions, or you can download the compressed tarball and install from source. When it's installed, open a terminal, switch to the root user, and type nethogs. You should see each application name and its PID along with how much data it has sent and received, similar the output of the top command. The information is updated in real time so you don't have to relaunch nethogs every time you launch a new application.
"By default the refresh rate is 1 second, but you can change it anything you like with the -d command option. Also by default, the transfer is shown in KBps (kilobytes per second) but this too can be changed. While nethogs is running, press the m key to cycle through the available options for displaying the data transfer. The options are KBps, Bps, and MBps."
