Siemens CPU 31 Series Technical Data Manual page 46

Communication
3.2 Communication services
Routing: Example of a TeleService application
The figure below shows the example of an application for remote maintenance of an S7
station using a PG. The connection to other subnets is here established via modem
connection.
The lower section of the figure shows how to configure this in STEP 7.
3-14
CPU 31xC and CPU 31x, Technical Data
Manual, 01/2006 Edition, A5E00105475-06