What it is
This is the Siemens 6GK7343-1GX11-0XE0, the CP 343-1 IT communications processor. It gets your S7-300 onto Industrial Ethernet with ISO and TCP/IP, plus S7 communication, fetch/write, send/receive, even email and web serving. Runs at 10/100 Mbit/s.
Mounting and integration
Connects SIMATIC S7-300 to Industrial Ethernet via ISO and TCP/IP, supporting S7 communication, fetch/write, email, and web serving at 10/100 MBITS.