I need to know my bandwidth and consumed internet bandwidth and downloaded data size like that. I tried this, but its not getting total downloaded packs size.
Have a look on "Conky". At the beginning it seems not to be easy to configure - but there are many templates you can use. Here you can find many templates - of course you can adjust them to your needs
Also usefull is "Conky Manager" (http://ubuntuguide.net/install-conky-manager-2-0-2-ubuntu-1404).
The red recangle shows the current up- / down-speed and the total size of uploaded / downloaded data. These values will be resetted after reboot.
@Daniel: Sorry for posting a comment rather than as an answer :)
There are several options. I have found that the most simple one is to install
sudo apt install gnome-system-monitor
Then click on resources. I have it selected in the autostart apps and just alt + tab when I want to know. I used to use the Gnome addon, but I don't use gnome anymore (hint devs). On the downside, it is only measures each session.