Siemens Simatic S7-300 CPU 31xC and CPU 31x S7-300 - Manual (Page 54)

Communication
3.3 S7 connections
CPU 31xC and CPU 31x, Technical data
3-26
Manual, Edition 08/2004, A5E00105475-05
3.2.10.5 SNMP communication service
Availability
The SNMP communication service is available for CPUs with integrated PROFINET
interface and Firmware 2.3.0 or higher.
Properties
SNMP (Simple Network Management Protocol) is a standard protocol for TCP/IP networks.
Reference
For further information on the SNMP communication service and diagnostics with SNMP,
refer to the PROFINET System Description.
3.3 S7 connections
3.3.1 S7 connection as communication path
An S7 connection is established when S7 modules communicate with one another. This
S7 connection is the communication path.
Note
Global data communication, PtP communication, communication with TCP/IP and SNMP do
not require S7 connections.
Every communication link requires S7 connection resources on the CPU for the entire
duration of this connection.
Thus, every S7 CPU provides a specific number of S7 connection resources. These are
used by various communication services (PG/OP communication, S7 communication or
S7 basic communication).