DIAMETER: Difference between Session Termination Request/Answer and Disconnect Peer Request/Answer ?

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

I have not detailed knowledge of diameter protocol but still can share whatever I know.
Both the "Session Termination Request" and "Session Termination Answer" messages are exchanged between diameter server and client in order to stop the session and clean the resources associated with the session from both the end.

Disconnect Peer Request and Answer messages are exchanged between the Diameter nodes to close the transport connection(i.e. TCP or SCTP) between them. When a diameter client issues disconnect peer request message towards its peer, it also mention cause for disconnection.
For the detailed answer, please check the RFC3588.

Answer 2

Hi Ganesh,

First we need to understand the difference between connection and session.

                     +--------+          +-------+          +--------+
                     | Client |          | Relay |          | Server |
                     +--------+          +-------+          +--------+
                              <---------->       <---------->
                           peer connection A   peer connection B

                              <----------------------------->
                                      User session x

A connection refers to a transport-level connection between two peers that is used to send and receive Diameter messages.
A session is a logical concept at the application layer that exists between the Diameter client and the Diameter server; it is identified via the Session-Id AVP.

So now u can understand where DPR/DPA and STR/STA will fit.

I Hope you get some idea.