where your servers are located?

server is located at client place, we access the client 
system by using a VPN

A virtual private network (VPN) is a secure way of connecting to a private Local Area Network at a remote location, using the Internet or any unsecure public network to transport the network data packets privately, using encryption. The VPN uses authentication to deny access to unauthorized users, and encryption to prevent unauthorized users from reading the private network packets. The VPN can be used to send any kind of network traffic securely, including voice, video or data.
VPNs are frequently used by remote workers or companies with remote offices to share private data and network resources. VPNs may also allow users to bypass regional internet restrictions such as firewalls, and web filtering, by "tunneling" the network connection to a different region.
Technically, the VPN protocol encapsulates network data transfers using a secure cryptographic method between two or more networked devices which are not on the same private network, to keep the data private as it passes through the connecting nodes of a local or wide area network.