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The 3G network throttling preset

This is the standard recommendation for 3G throttling:

  • Latency: 150ms
  • Throughput: 1.6Mbps down / 750 Kbps up.
  • Packet loss: none.

These exact figures are used as the WebPageTest "Mobile 3G - Fast" preset and Lighthouse's throttling default.

Throttling basics

  1. The DevTools network throttling, which Lighthouse uses, is implemented within Chrome at the request-level. As a result, it has some downsides that are now summarized in this doc: Network Throttling & Chrome - status. The TLDR: while it's a decent approximation, it's not a sufficient model of a slow connection. The multipliers used in Lighthouse attempt to correct for the differences.
  2. Proxy-level throttling tools do not affect UDP data, so they're not recommended.
  3. Packet-level throttling tools are able to make the most accurate network simulation.

How do I get high-quality packet-level throttling?

If you want to use more accurate throttling, read on.

This Performance Calendar article, Testing with Realistic Networking Conditions, has a good explanation of packet-level traffic shaping (which applies across TCP/UDP/ICMP) and recommendations.

Using comcast for network throttling

The comcast Go package appears to be the most usable Mac/Linux commandline app for managing your network connection. Important to note: it changes your entire machine's network interface. Also, comcast requires sudo (as all packet-level shapers do).

Windows? As of today, there is no single cross-platform tool for throttling. But there are two recommended Windows-specific network shaping utilities: WinShaper and Clumsy.

comcast set up

# Install with go
go get github.com/tylertreat/comcast
# Ensure your $GOPATH/bin is in your $PATH (https://github.com/golang/go/wiki/GOPATH)

# To use the recommended throttling values:
comcast --latency=150 --target-bw=1600 --dry-run

# To disable throttling
# comcast --stop

Currently, comcast will also throttle the websocket port that Lighthouse uses to connect to Chrome. This isn't a big problem but mostly means that receiving the trace from the browser takes significantly more time. Also, comcast doesn't support a separate uplink throughput.

Using Lighthouse with comcast

# Enable system traffic throttling
comcast --latency=150 --target-bw=1600

# Run Lighthouse with it's own throttling disabled
lighthouse --disable-network-throttling # ...

# Disable the traffic throttling once you see "Retrieving trace"
comcast --stop