[vp8989]

They are 2 distinct concepts for sure, but if you also need to track each request independently then it would seem more robust to generate a separate Id for that from within the scope of your system. I don't think you would want to rely on a client to differentiate "physical" requests for you.

Maybe "Logical-Request-Identifier" and "Physical-Request-Identifier"?

[karmakaze]

On the surface this sounds about right, but how do we ensure that we only create one of these? Every layer will want to create a new id as not trusting the id given to it as 'new'. Having the actual client generate both is the simplest.