CAN iso 15765-4 (can 11/500) . Whats the difference between SERVICE & DIAGNOSTIC

[SyRus16]

Hi.


CAN iso 15765-4 (can 11/500) or CAN iso 15765-4 (can 29/500)

There is closed (IPDM) and open(BCM) CAN in a vehicles.
What I mean by open is that the messages between ECUs(NODs) the SERVICE massages and DIAGNOSTIC messages from DIAG device (OBD2/port) are flays out together on the same bus.

When on closed CAN with IPDM service messages are hidden behind the gateway.

So my question is

How to determine, distinguish the SERVICE message and DIAGNOSIC message? What is the difference between them?

Im attaching the protocol description PDF. I could not find any info on that in PDF.

[SyRus16]

I guess nobody knows...

Maybe you know the place I can ask this question?