NDT measures “bulk transport capacity”: the maximum date rate that TCP can reliably deliver data using the unreliable IP protocol over an end-to-end Internet path. TCP’s goal is to send data at exactly the optimal rate for the network, containing just the right mix of new data and retransmissions such that the receiver gets exactly one copy of everything. Since its creation, the TCP protocol has consistently made improvements to the way it accomplishes this task, consequently, NDT has also incrementally changed to reflect these improvements. The most recent improvements, including support for TCP BBR, are available in ndt7. On July 24th, we announced the start of migration of NDT clients to the latest protocol version. As of today, approximately 50% of clients are using ndt7. As the ndt7 measurements become the majority of the NDT dataset, the M-Lab team is considering what we do and do not know about whether and how changes to the NDT protocol have affected M-Lab’s longitudinal NDT dataset over time.
Following the general availability of the ndt7 protocol, we will be working with NDT client integrators to support their migration to ndt7. As they do, the NDT dataset will shift from predominantly ndt5 to predominantly ndt7. As part of assessing our readiness for this larger effort, a pilot was started on July 8.
The new ndt7 protocol for the Network Diagnostic Tool (NDT) is now generally available on the M-Lab platform. Since 2009, NDT has been the premier TCP performance measurement service test hosted by M-Lab. During its history on the platform, NDT has produced the largest test volume to date, spanning the longest history. Since late 2018, M-Lab has worked with researcher Simone Basso to develop the ndt7 protocol and archival data format.