Question about aliases in pcap 

The Source and Destination of packets define IP addresses that are aliases (ipcas_21:73:N for the source and the Iec-Tc57_01:00:01 for the destination). The Destination is always the IP of a single machine (Iec-Tc57_01:00:01 ). How is the topology composed? Are there N IEDs that send data to a single server, or the Iec-Tc57_01:00:01 is a broadcast address? 

Thanks in advance. 