sudo apt-get install network-manager
Will fail. Note what dependencies are needed to install the package.
Mine were-
The following NEW packages will be installed:
iputils-arping libnl-route-3-200 modemmanager network-manager network-manager-gnome usb-modeswitch usb-modeswitch-data wpasupplicant
The download will fail obviously with error:
Failed to fetch
http://us.archive.ubuntu.com/ubuntu/pool/main/libn/libnl3/libnl-route-3-200_3.2.3-2ubuntu2_amd64.deb
Could not resolve 'us.archive.ubuntu.com
Download all such links which gives above error including network-manager by some other system. I downloaded the following links-
http://us.archive.ubuntu.com/ubuntu/pool/main/libn/libnl3/libnl-route-3-200_3.2.3-2ubuntu2_amd64.deb
http://us.archive.ubuntu.com/ubuntu/pool/main/w/wpasupplicant/wpasupplicant_0.7.3-6ubuntu2.2_amd64.deb
http://us.archive.ubuntu.com/ubuntu/pool/main/i/iputils/iputils-arping_20101006-1ubuntu1_amd64.deb
http://us.archive.ubuntu.com/ubuntu/pool/main/u/usb-modeswitch-data/usb-modeswitch-data_20120120-0ubuntu1_all.deb
http://us.archive.ubuntu.com/ubuntu/pool/main/u/usb-modeswitch/usb-modeswitch_1.2.3+repack0-1ubuntu2_amd64.deb
http://us.archive.ubuntu.com/ubuntu/pool/main/m/modemmanager/modemmanager_0.5.2.0-0ubuntu2_amd64.deb
http://us.archive.ubuntu.com/ubuntu/pool/main/n/network-manager-applet/network-manager-gnome_0.9.4.1-0ubuntu2.3_amd64.deb
The links above does not contain the link of network-manager itself. You can download it from here; from a software mirror close to you. Take care to choose the appropriate architecture (amd64 for 64-bit, i386 for 32-bit), and release version of your installed OS.
Now copy the deb files to /var/cache/apt/archives/
Run sudo-apt-get install network-manager
in terminal.
Now it will pick up deb files from cache and will not prompt to download them.
If all goes well network-manager will be installed.
Finally reboot the system.
sudo dpkg -i *.deb
from the terminal.