iperf3 is a tool for measuring the achievable TCP, UDP, and SCTP
throughput along a path between two hosts.  It allows the tuning of
various parameters such as socket buffer sizes and maximum attempted
throughput.  It reports (among other things) bandwidth, delay jitter,
and datagram loss.  iperf was originally developed by NLANR/DAST.

iperf3 is a new implementation developed from scratch at the Energy
Sciences Network (ESnet).  Among its goals were a smaller, simpler
code base (compared to its predecessor, iperf2) and a library version
of the functionality that can be used in other programs.  Note that
iperf3 does not interoperate with with iperf 2.x.