What is network quality?

Network quality can mean different things, depending on the context. When we talk about wireless link quality, often we focus on Layer 1 properties like RSSI, noise, the Tx/Rx rate etc. However, today I want to focus on Transport layer metrics that can be collected with the new `networkQuality` tool.

Usage

It seems that Apple has quietly added a new tool in macOS Monterey for measuring your device's Internet connectivity quality. You can simply call the executable `networkQuality`, which executes the following tests:

- Upload/download capacity (your Tx/Rx bandwidth essentially)
- Upload/download flows, this seems to be the number of test packets used for the responsiveness tests
- Upload/download responsiveness measured in Roundtrips Per Minute (RPM), which according to Apple, is the number of sequential round-trips, or transactions, a network can do in one minute under normal working conditions

The capacity is roughly the same metric you could expect from tools like Fast.com from Netflix, or OOkla's Speedtest.

For example:
<code>
λ networkQuality
==== SUMMARY ====
Upload capacity: 14.696 Mbps
Download capacity: 21.661 Mbps
Upload flows: 20
Download flows: 12
Responsiveness: Low (103 RPM)
</code>

Why the macOS tool wins in some aspects

While these tools measure a few more metrics like latency to a target server, they both only measure capacity, and do this only in serial mode (the download and upload speed tests are done sequentially one after the other).

On the other hand, `networkQuality` measures the upload/download capacity and responsiveness in parallel by default (can be overridden to sequential mode with the `-s` argument). In my opinion, this test is closer to some real-world use-cases, which are also mentioned in the official Apple support docs: video chat and voice calls. In these scenarios, you not only receive a media stream, but also transmit one (for example, the feed from your webcam, screen sharing, or your microphone), so a proper network test needs to simulate both in parallel.

The tool will also provide you with a simple classification of your network quality from `Low`, `Medium` and `High`.

```bash
λ networkQuality -s
==== SUMMARY ====
Upload capacity: 14.035 Mbps
Download capacity: 57.650 Mbps
Upload flows: 20
Download flows: 20
Upload Responsiveness: Low (107 RPM)
Download Responsiveness: High (2253 RPM)
```

UPDATE: Hello HN! Thanks to everyone for the great comments and suggestions. Just wanted to include something the folk have discovered that I didn't have time for: the tool uses Apple's CDN at `https://mensura.cdn-apple.com/api/v1/gm/config` as a target for the requests.

Conclusion

Of course, Apple's tool is not a full replacement for `ping` or speedtest-cli, but it provides pretty useful connectivity tests that I haven't seen in common CLI tools yet, and it's nice that it is included in the new release.

If you use Emacs, you can now also run this tool using the osx-lib package.