One possible option could be that the data can be stored as a string in the code or as a file. The packet payload can be modified to contain custom data which can be read from a input file or a string. Refer: https://support.tetcos.com/support/solutions/articles/14000041020-how-do-i-change-the-payload-of-a-packet-in-netsim-https://support.tetcos.com/support/solutions/articles/14000085089-how-to-read-the-payload-from-a-file-in-the-application-layer-
The data received or sent from a node can be visualized using wireshark packet capture. Refer: