Under which protocol an RFC is running?

In the ABAP stack of SAP Web AS an RFC could be called in different ways. eg:

- by the same system (CALL FUNCTION...)

- by an external system ( CALL FUNCTION .. DEST sid)

- as a web service (SOAP)

- and probably others ...

Which is the more official way to determine the running protocol at runtime?

Querying SY-CPROG it is possible to understand the environmnet (SAPMHTTP, SAPMSSY1) but maybe you know a better way.

Sergio