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Network Information API

Thomas Steiner ([email protected])

Introduction and background

More and more devices are permanently connected to the Internet, and connectivity is a fundamental requirement for many. Network connectivity depends on a lot of factors, some of which include the connection type (e.g., Wi-Fi, 3G, 4G, 5G, etc.), but also factors like the device's physical location (e.g., Wi-Fi on a moving train), or the user's preferences (e.g., a desire to not overly tax a data connection shared with others).

Naive assumptions like "connected to Wi-Fi always means connectivity is granted and data is cheap" or the opposite "connected to cellular always means connectivity is spotty and data is expensive" no longer hold true, and in many cases never did.

The Network Information API aims to provide a standard approach for web applications to query the current network status in a meaningful and privacy-preserving way.

Distinction from the save data use case

Getting information about the network connection is not to be treated as equivalent to a necessary desire to save data. For example, a web application that downloads data via the BitTorrent protocol may voluntarily want to limit itself to only a percentage of the available bandwidth as to not block other browsing activity, but the objective is not saving data.

The save data use case is dealt with in the Save Data API spec. Web developers can also make use of the prefers-reduced-data user preference media feature in CSS (@media (prefers-reduced-data: reduce) { /*…*/ }) or JavaScript (if (window.matchMedia('(prefers-reduced-data: reduce)').matches) { /*…*/ }).

Definitions

Metered connection

A metered connection is an Internet connection that has a data limit associated with it. Examples include mobile data plans with a certain amount of included data, but also ad-hoc hotel Wi-Fi access, or even certain home Internet data plans. Once the data limit is reached, the connection is interrupted, or continuous data usage is charged at an additional (commonly high) cost. It is typically the desire of the user to remain within the caps of the data plan, and not be charged for data usage above the cap.

Sustained connection speed

The sustained connection speed is a numerical means to express what kind of transfers the current connection is suitable for. Nielsen's Law of Internet Bandwidth has shown that users' bandwidth grows by 50% per year. Therefore, rather than use fixed speed labels like 3G, 4G, or 5G (that might be based on theoretically technically possible maximum bandwidth or field-measured actual bandwidth) or meaningless labels like Wi-Fi, the Network Information API uses open-ended bandwidth ranges to express the sustained connection speed. These ranges are measured in bit per second (bit/s) and can be used in conjunction with SI prefixes (e.g., 1 kbit/s = 1,000 bit/s, 1 Mbit/s = 1,000 kbit/s, 1 Gbit/s = 1,000 Mbit/s, or 1 Tbit/s = 1,000 Gbit/s). For example, 4K video commonly requires 20 Mbp/s sustained speed according to the popular streaming service YouTube. The means through which the sustained connection speed is realized (e.g., via a Wi-Fi or an ethernet connection) is not exposed.

Origin of the data

Metered connections

Some operating systems let the user declare certain networks as metered networks, which typically disables features like syncing or automatic updates.

Network statistics

Operating systems like Windows or macOS make realtime network statistics available in their Task Manager respectively their Activity Monitor apps. On the command line, many operating systems offer the nettop tool or other means to obtain network statistics. User agents can, at their own discretion, report these statistics in buckets of exponentially growing size of bit per second ranges.

  • The Windows Task Manager:

    Task Manager on Windows.

  • The macOS Activity Monitor:

    Activity Monitor on macOS.

  • The macOS networkQuality tool:

    $ networkQuality

==== SUMMARY ====
Upload capacity: 11.102 Mbps
Download capacity: 51.989 Mbps
Upload flows: 12
Download flows: 12
Responsiveness: High (1666 RPM)

  • The nettop tool:

    nettop on the macOS command line.

Examples

Downloading non-essential content

let nonEssentialContentLoaded = false;

async function downloadNonEssentialContent() {
  if (nonEssentialContentLoaded) {
    return;
  }
  if (!navigator.connection.metered) {
    await fetch('https://example.com/non-essential-content/');
    nonEssentialContentLoaded = true;
  }
}

if (!navigator.connection.metered) {
  downloadNonEssentialContent();
}

navigator.connection.addEventListener('change', downloadNonEssentialContent);

Limiting bandwidth usage

const initialSustainedSpeedInBytes = navigator.connection.sustainedSpeed / 8;

// https://github.com/webtorrent/webtorrent/blob/master/docs/api.md#client--new-webtorrentopts
const client = new WebTorrent({
  // Max 50% of the available bandwidth.
  downLimit = 0.5 * initialSustainedSpeedInBytes,
});

navigator.connection.addEventListener('change', (event) => {
  const currentSustainedSpeedInBytes = event.connection.sustainedSpeed / 8;
  // https://github.com/webtorrent/webtorrent/blob/master/docs/api.md#clientthrottledownloadrate
  client.throttleDownload(0.5 * currentSustainedSpeedInBytes);
});

Adaptive loading based on client hints

  1. The client makes an initial request to the server. 
    GET / HTTP/1.1
Host: example.com
  2. The server responds, telling the client via Accept-CH that it accepts the Sec-CH-Metered-Connection and the Sec-CH-Sustained-Speed client hints, and that it also varies the response on the former, as conveyed by Vary. 
    HTTP/1.1 200 OK
Content-Type: text/html
Accept-CH: Sec-CH-Metered-Connection, Sec-CH-Sustained-Speed
Vary: Sec-CH-Metered-Connection
  3. The client then later makes a follow-up request for /list-of-products, telling the server via Sec-CH-Metered-Connection that it is on a metered connection and via Sec-CH-Sustained-Speed that its sustained speed is in the bucket of 50,000,000 bps (50 Mbps). 
    GET /list-of-products HTTP/1.1
Host: example.com
Sec-CH-Metered-Connection: 1
Sec-CH-Sustained-Speed: 50000000
  4. The server can then tailor the response to the client's preferences accordingly and, respecting the metered connection, for example, choose to not return all possible products, but just a subset. Since the connection speed permits it, the server can choose to include product videos in the response, but not autoplay them, because the connection is metered.