The server has to support web sockets. After a first handshake in HTTP, the server and the client open a socket connection. The server must be able to understand and accept this handshake.
In my last project we run quite successfully web socket connections using the last Jetty version.
27/02/2014:
Now I’m also implementing websockets under .net with XSockets.net and works like a charm, you don’t even need a web server (self hosting). The WebSocket implementation of ASP.NET works also quite good.