The following formula is used to calculate link throughput in NetSim:
Link Throughput (Mbps) = Total Bytes transmitted in the link * 8 / Simulation Time (Micro sec)
Useful references:
what-is-the-difference-between-link-throughput-and-application-throughput-in-netsim-
why-do-i-sometimes-get-zero-throughput-when-path-loss-is-enabled-in-wireless-networks-
finding-the-saturation-throughput-in-a-network-
can-i-get-the-instantaneous-throughput-for-applications-links-