I have more than 100 Clients .
1) Each clients are behind router. (mean external IP always change)
2) Each Clients have its own local DB SQL.
3) Each Clients using Windows Application c#.
4) Each clients have not install IIS.
5) Each Clients will have internet Connection.

My Server is Web application(ASP .Net) and on open network and have Static IP.

There is no LAN networking between Clients...