How to get deliveryfailurestatus , back to calling service.


We are having following scenario :
A flat file document is sent to an FTP Location via TN.
pkg A
Service A ( prepares the ff document and calls wM remoteinvoke service)
pkg B
service B1 ( submits document to TN )
service B2 ( delivers document to FTP Location )
Sevice A calls remote invoke service to submit the
document to TN using service B1 … TN in its processing rule calls service B2
to deliver the document to FTP Location.
How do i get failure mesage in the Service A , if delivery to FTP Fails in Service B2 , because based on fail / sucess Service A needs to
do the further processing of business logic. service B2 is using … but its o/p is not available for Service A
What would be the approach to handle this scenario best.