ndt7 Introduction

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.

The ndt7 protocol measures the application-level download or upload performance using WebSockets over a single TCP connection. The ndt7 protocol answers the question of how fast you could pull/push data from your device to a typically-nearby, well-provisioned web server by means of commonly-used web technologies. This is not necessarily a measurement of your last mile speed. Rather it is a measurement of what performance is possible with your device, your current internet connection (landline, Wi-Fi, 4G, etc.), the characteristics of your ISP and possibly of other ISPs in the middle, and the server being used. The ndt7 protocol allows clients to measure “goodput”: the speed measured at application level, without including the overheads of WebSockets, TLS, TCP/IP, and link layer headers. The ndt7 protocol also allows clients to report “throughput” because the protocol also includes kernel-level information from TCP_INFO.

A design goal of the ndt7 protocol was to be able to build clients that are simple and easy to maintain over time. For example, a complete Go language ndt7 client can be implemented in just 151 lines, and a complete JavaScript client can be implemented in just 122 lines. We are publishing two reference client implementations here:

On the M-Lab platform, ndt7 uses BBR TCP. BBR is a new congestion control algorithm that uses the network more efficiently. It does so by explicitly measuring the two most important network parameters: the maximum bandwidth and minimum roundtrip time. BBR uses these parameters to precisely model network behavior, making it much more efficient than prior TCP implementations. These parameters also happen to be the most important from a measurement standpoint, which is why we expect BBR to revolutionize Internet measurement.

Because of the benefits of BBR and simplicity of the ndt7 protocol, ndt7 will be the preferred protocol for new integrations. We have begun the process of migrating existing clients to the ndt7 protocol and initial analysis of the performance benefits of BBR is extremely promising. We will soon share more information about current migrations and how this will improve our data and affect longitudinal analysis.

For a recent introduction to BBR see: TCP BBR - Exploring TCP congestion control | by Andree Toonk

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