The native screen sharing on the mac is VNC. Port 311 is for OS X Server Admin, which is a different thing entirely. It's only listening on OS X Server, it's not screen sharing, and you connect to it using the Server Admin app that's part of the OS X Server Tools.
You can connect to the native OS X screen sharing with a VNC app like Chicken of the VNC or with the native screen sharing app which lives in /System/Library/CoreServices/Screen Sharing.app (which is nothing more than a limited VNC client)
The only actual difference between regular VNC and the screen sharing that's built in to OS X is the authentication. OS X includes an additional authentication mechanism which allows you to connect with user/password credentials, where the native, compatible VNC only expects a host-specific password (with no provision for multiple users). You can enable or disable the compatible authentication in System Preferences, but in either case it's still just the VNC protocol that's doing the screen sharing.