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

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:

NameD•Tective — mDNS over AppleTalk

[From the Archives of Amusing Technology…] Back in the ’90s, Dave Fisher and I created NameD•tective, a Macintosh control panel that gave any Mac on the Dartmouth network a static DNS name.

It used Name Binding Protocol to let someone create a DNS name based on their name plus their AppleTalk zone. The DNS name had the form: person-name.AppleTalk-zone… The NameD•tective server looked up the NBP name, and returned the computer’s current IP address. Here’s a screen shot of the archived page from Dartmouth’s website from the Wayback Machine:

The page above shows an example: was a server in my office that distributed information to other developers in the Kieiwt building. NameD•tective probably didn’t get broad use at Dartmouth, but it was a neat demonstration project. It led Dave and me to develop the MacDNS software that was shipped as part of Apple’s Internet Connection Kit.

Today, computer naming is much simpler. Modern operating systems let a computer specify a mDNS (multicast DNS) name that can be directly looked up to find a host that provides the service.