perfSONAR is a critical component of the Science DMZ - without perfSONAR, it would be very difficult to detect and diagnose the performance problems which inevitably arise in complex network-based workflows, and to do the necessary performance engineering work to ensure that science networks remain in good working order as effective scientific tools.
perfSONAR is several things - it is a software development collaboration, it is a suite of network test and measurement tools, and it is the deployed international test and measurement infrastructure based on the toolset developed by the perfSONAR collaboration. Several important perfSONAR resources include:
The perfSONAR web site, www.perfsonar.net
The global perfSONAR services directory at http://stats.es.net/ServicesDirectory/
Specific documentation for perfSONAR operation on the Fasterdata knowledgebase at http://fasterdata.es.net/performance-testing/perfsonar/