In order for a real-time capable Ethernet data network protocol to shorten the cycle time of the transmission cycles in a real-time capable Ethernet data network it is provided that a plurality of slaves (S1, S2, S3, S4) is combined into a sum frame group (SG) and one of these slaves (S1, S4) serves as initiator slave of the sum frame group (SG) and transmits a sum frame data packet (DPSR) to the other slaves (S1, S2, S3, S4) of the sum frame group (SG), so that these other slaves (S1, S2, S3, S4) of the sum frame group (SG) receive the sum frame data packet (DPSR) in sequence, each of these slaves (S1, S2, S3, S4) writes its data (D1, D2, D3, D4) into the sum frame data packet (DPSR) and the last slave (S4, S1) of the sequence transmits the sum frame data packet (DPSR) to the master (M).