Siemens Simantic Net NCM for Industrial Ethernet S7 - Manual (Page 162)

Programming FCs (Functions) and FBs for S7 Ethernet CPs
162
SIMATIC NET NCM S7 for Industrial Ethernet
C79000-G8976-C129–06
Notice
Please not the following special feature on TCP connections:
With the S7-CPs for S7-400, you must use FC AG_LRECV on TCP connections!
With the latest S7-CPs for S7-300, you must also use FC AG_RECV for TCP
connections.