This document describes the use of perfSONAR as a network performance measurement tool, and encourages its deployment at sites in support of networking for data-intensive research. perfSONAR is an open source toolkit that allows measurement of throughput, loss, latency and the path traffic takes between two measurement points. When run with the MaDDash web front end, it allows measurement over time of network characteristics between multiple sites in a research community, presenting the results in an intuitive mesh/matrix format.