Siemens CPU 31 Series Technical Data Manual page 44

Communication
3.2 Communication services
The figure below shows the MPI access to PROFINET via PROFIBUS CPU 1 (315-2 DP, for
example) is the router for subnet 1 and 2;
CPU 2 is the router for subnet 2 and 3.
Routing network nodes: MPI - DP - PROFINET
3-12
CPU 31xC and CPU 31x, Technical Data
Manual, 01/2006 Edition, A5E00105475-06