Hi Subhojit!
Look at this examples:
http://scn.sap.com/docs/DOC-35665
**************** - Demonstration on using SYNC/ASYNC Bridge in BPM
Also take a look at Integration process "BpmPatternSyncAsyncBridge" in http://sap.com/xi/XI/System/Patterns namespace of SAP BASIS SCV in ESR.
Regards, Evgeniy.