Network Manager was introduced in Ubuntu 14.04 Trusty Tahr instead of the traditional Linux networking model. So to restart network service you should use sudo service network-manager restart instead of sudo service networking restart.
howopensource@esprimo:~$ sudo service network-manager restart network-manager stop/waiting network-manager start/running, process 12737 howopensource@esprimo:~$
Here are couple of more ways to achieve the same task.
howopensource@esprimo:~$ sudo ifconfig eth0 down && sudo ifconfig eth0 up
howopensource@esprimo:~$ sudo ip link set eth0 down && sudo ip link set eth0 up
Both commands do the same task. When you are accessing Ubuntu via SSH do not forget to run both down and up otherwise you may just disable network service. For more info look into the screenshots.
Network Manager is the new tool for Ubuntu network that “Just Works”. The computer should use the wired connection when available, but automatically switch to a wireless connection when the user unplugs the network cable and walks away from the desk. And when the user plugs the computer back in, the computer should switch back to the wired connection. Idea is that user should not even notice that their connection has been managed. They should simply see uninterrupted network connectivity whatever it is connected. Also Network Manager has VPN support which based on a plug-in system and Ubuntu makes easy to use those connections. For more info read the following article. It also has nice GUI applet that allows user to manage active connections.