The diagram shows a top-level coordinator and an interposed coordinator . The top-level coordinator is responsible for driving the original, top-level transaction to completion or rollback. The interposed coordinator manages its participants in a subordinate transaction, but it cannot act autonomously. From the point of view of the parent coordinator, it appears to be another participant in the top-level transaction. The interposed coordinator operates as an intermediary. It forwards incoming prepare and commit / rollback messages to its participants, combining their responses and returning them back to its parent coordinator.