I have a web service in C# and would like to have a nested inner class, that abstracts away the session collection, something like this:
public class Service
Nested classes in C# aren't like (non-static) inner classes in Java. There is no implicit reference to an instance of the containing class - so you can't use any instance members of the containing class without an explicit reference.
However, you do have access to all private members of the containing class - with a suitable reference for instance members.