Exception handling in Rosettanet development

I am working on implementing Rosettanet Pip 7B1 using webMethods 4.6 with one of my partners. TN as well as IS is installed on the DMZ and the backend(SAP) connection part (developer service) is on one of the internal servers. Pip data is passed from the DMZ to the internal server through a developer service which does a http to the internal.We have one problem.

In case connection between the DMZ and internal does not work or SAP is down at the moment, the conversation would end successfully even though the actual transaction is not. Could someone please suggest how to handle the exception/retries etc. while doing a server to server transfer of data by http. Also, is this method of transferring data through htts from DMZ to INT OK.

Any help will be greatly appreciated.