Diameter: How does a Diameter node make out that answer message is received by peer ?

Question

I know Diameter client can re-transmit the request message until it receives the answer message.
But what about when a Diameter node has sent answer message to the last received request from its peer and that's is not received but its peer. In this case, from Diameter client node transaction is not completed since it did not receive answer message but from other node point of view it has responded with answer and transaction is completed.

Answer 1

The responder forgets about it after sending the answer, it can't be certain. But the requestor is required to track the transaction, timeout and re-send the request if necessary.

This is where duplicate detection becomes important. The responder should detect if he receives a duplicate request, and application logic should ensure that the action is not performed twice (if it causes harm like double billing). Diameter protocol itself has a Duplicate bit , but I think applications (say OCS) may need ability to detect duplication at application level too - say identifying duplicate CDRs.