The Siemens 6ES7972-0EM00-0XA0 is a TS Adapter IE modem for the SIMATIC S7 family — a spare part that bridges a teleservice RS-232 connection and an integrated analog modem to Ethernet, powered by an external 24 VDC supply. This is the box you bolt onto an S7 rack when you need remote dial-in for programming or diagnostics over a phone line, then route it onto the plant network.
Mounts on a DIN rail next to the S7 CPU or in the same cabinet. The RS-232 side connects to the CPU's MPI/DP port or a CP card; the analog modem side takes a standard RJ11 phone line. Ethernet uplink goes to the plant switch. External 24 VDC supply — watch the polarity on the terminal block; the modem draws enough that you don't want to share a marginal power supply with a bunch of other loads. No special software beyond the standard Teleservice configuration in Step 7.