You can pass the connection into the `start_server` method, and it'll be passed along to the initialize method of `CallbackHandler`. That would avoid the need for the global variable, and would make `CallbackHandler` easier to reuse.

> (Object) start_server(server, port = nil, handler = nil, *args, &block)
> ...
> Arguments passed into start_server after the class name are passed into the constructor during the instantiation.
http://eventmachine.rubyforge.org/EventMachine.html#start_server-class_method