What is the difference between an OpenID provider and an OpenID WebRing single sign-on provider?

I look at DotNetOpenAuth samples and there are two examples of an OpenID provider; both the OpenID provider and the OpenID Web Ring single sign-on provider.

Does anyone know the differences between the two and in which scenario should each be used? I specifically want to see when to use the SSO Web Ring Provider. I know what the OpenID provider offers.

To give some context; I need to build an OpenID provider to provide single sign-on for several web applications I'm working on.