performance: user reports of different performance from ndt5 and ndt7

[stephen-soltesz]

We've received several user reports of different performance from ndt5 vs ndt7 that could be a sign of something more widespread.

Case 1:

• User reported leasing a symmetric 100Mbps connection. Typical traffic performed poorly, ~6Mbps down, but 90Mbps up still. Confirmed this using speedtest.net. However ndt7 from Google speed test onebox reported 60-90Mbps down. Similarly from the Nest Wifi via Google Home, also reported 90Mbps down. However, speed.measurementlab.net reported slow performance, ~6Mbps.
• I confirmed with the users that ndt7 was actually downloading the data using the websocket messages from ndt server, i.e. TCPInfo.BytesAcked. It was not a client reporting bug.

Case 2:

• M-Lab support user reported a 12x difference in the download speed from Google onebox (80-150Mbps) vs speed.measurementlab.net (6-12Mbps).

Cause is unidentified.

[bassosimone]

I think this could be explained by BBR vs. Cubic in both cases (but @mattmathis surely knows better).

[laiyi-ohlsen]

Useful to include MinRTT if possible

[critzo]

Related @support ticket:

• https://support.measurementlab.net/#ticket/zoom/419