Recently I had an opportunity to architect/design, develop, develop, test and deploy an enhanced Interface Monitoring Solution for Salesforce.com - SAP/PI - SAP project for one of our clients. This blog is a continuation to my previous blog SFDC-SAP/PI-SAP Integration: Project delivered, Lessons learnd
The interface between Salesforce.com - PI - SAP was designed and developed using Apex SOAP APIs.

At a high level, the monitoring solution should deliver the following options:
  • Integration Logger mechanism to capture request-response payload.
  • Scheduled reports for to send consolidated failed records interface-wise.
  • Email notification to system admins for each failure.
  • Display of SAP error message on the UI for end users’ convenience and know-how.
  • Retriggering UI mechanism for sending failed records to the external system, in this case, SAP/PI.
  • In case of IP white listing issue, there should be a mechanism to troubleshoot/identify the IP address from which your SFDC instance is sending payload request to the external system.

You can leverage various Salesforce features to accomplish the above mentioned options. 
Please do add if you have some more thoughts on this topic.
Happy Apex Integration..  :)