VPN: 

When using a client-to-server VPN (see box below), a remote client requests a resource from its corporate LAN. The computer then dials up an ISP to connect to the Internet and creates a logical connection to the corporate VPN server. This VPN server authenticates the client and manages encapsulation and encryption on the communications between the client and the resources on the corporate LAN.

  The graphic above depicts a client-to-server VPN where a remote user connects to a corporate VPN server using point-to-point tunneling protocol (PPTP). The use of PPTP allows enterprises to extend their own corporate network through private "tunnels" over the public Internet. Using this type of interconnection, a company no longer needs to lease its own lines for wide-area communication. Instead, enterprises can securely use the public networks because the communication packets are encrypted before they are sent through the tunnel.