Using Apple’s RPM tool

macOS Monterey ships with a tool that measures the responsiveness of your network connection. It saturates the network with traffic for 20 seconds, then measures the rate of short transactions to compute “Responses Per Minute.” Big numbers (above 2000) mean your network remains responsive when the network is heavily loaded. Small numbers (under 800 or so) mean your network isn’t responsive – potentially caused by bufferbloat.

There’s an iOS version described at https://support.apple.com/en-gb/HT212313

Stuart Cheshire and Vidhi Goel talked about the RPM tool at WWDC 2021. Apple also published an Internet-Draft that describes the RPM technique

Here’s a sample run from my Mac. The RPM tool displays my download and upload speeds (nominally 25mbps), and the number of simultaneous flows required to saturate the link (12, in this case). It shows the responsiveness as 1995 round-trips per minute. That’s really good: the average latency – even during heavy load – only increases a bit above the baseline (idle) 21 msec.

% /usr/bin/networkQuality -v
==== SUMMARY ====
Upload capacity: 22.657 Mbps
Download capacity: 23.755 Mbps
Upload flows: 12
Download flows: 12
Responsiveness: High (1995 RPM)
Base RTT: 21
Start: 11/7/21, 7:18:37 AM
End: 11/7/21, 7:18:47 AM
OS Version: Version 12.1 (Build 21C5021h)
%

Here’s a video that shows the tool in operation: https://youtu.be/e9DUTB9okMA

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