There you can see couple of interfaces, responsible for providing functionality of Xermes layers. If you are unsure about their importance, please return to architectural overview page and see through the diagram there first.

Most of interfaces consist of methods "up" and "down". Data bubble though down() methods as far as transport layer is reached. Transport layer sends and on the other side recieves (e.g. transports) data. There are appropriate "ups", passing data to higher levels. First level able to respond is intended to send an answer back, using downs... on the other side ups take it to the primary interrogator. This is the process information presented here to help you with understanding class model. To learn more about example session (with a lashings of bubbling up and down), study next page with seqeunce diagram, please.