Thank you very much. That helped a lot...
....and raised new questions

- why do I need an extra container for the diagram to provide parameters?
- why should the calling seq-Diagram be embedded in an interaction element? (It still works if I don't embed it) ?
- what are the parameters for, which I defined directly in the diagram
(note: they have been used to correctly show the parameter definition in a sequence overview diagram...) .... why can't they be used?
- and finally the result is not exactly what I intended to have:
-In the parameter dialog of the ref-fragment-box I can enter (in edit Parameters-dialog) a list of
- name
- Parameter (chosen from the pulldown)
- value
result:
--> displayed in the ref-Box is (name : Parameter)
--> I intended to see a comma sep. list of (Parameter=value)
as defined in UML Superstructure 2.2 on page 490 ff?

What is my misunderstanding?
I am still confused. Obviously I do not a understand a basic concept of EA...

Thank you
Ingo