Tests for Bufferbloat

Does the quality of your web browsing, voice call, or gaming degrade when someone’s downloading or uploading files? It may be that your router has “bufferbloat” - unnecessary latency/lag created by your router buffering too much data.

If the tests below show high latency (say, above 50 msec), read our recommendations at What can I do about Bufferbloat

Easy Test for Bufferbloat

The DSL Reports Speed Test makes accurate measurements of the download and upload speeds along with the latency during the test. The “Results + Share” button lets you see the numerical results or pass along a link to your friends. Watch the Bloat / No Bloat videos at Youtube to see how the test works.

A Quick Test for Bufferbloat

Other speed test sites only measure latency when the link is idle - and that only tells part of the story. You can get numeric latency measurements with those other speed test sites if you run a ping test simultaneously. To do this:

  1. Start a ping to google.com. You’ll see a series of lines, one per ping, typically with times in the 20-100 msec range.
  2. Run a speed test simultaneously. To do this, start one of the speed test services below:

    (fast.com now tests for latency under load but we’d like more folk to check their results against our quick test)

  3. Watch the ping times while the speed test is running. If the times jump up when uploading or downloading, then your router is probably bloated.

The Best Tests for Bufferbloat

The suite of tests we developed to diagnose bufferbloat and other connectivity problems are good to 40GigE, but require the Flent RRUL test suite Using the Flent tools, it is possible to get a good feel for how the connection is behaving while you tune your settings.

Other network performance and latency tools

  1. The Quick Test (described above) does a rudimentary job of measuring performance. Although it doesn’t run long enough to avoid the effects of Powerboost or other special cases implemented by ISPs, it can definitely point out situations where you’re “bufferbloated”.
  2. betterspeedtest.sh from CeroWrtScripts bundle is a script you can run on Linux/OSX or on CeroWrt to get concrete, repeatable tests of your network. It performs the same kind of download/upload test that is available from speedtest.net. It is better, though, because it continually measures your ping latency, and thus lets you know the performance and latency of each direction of data transfer.
  3. The netperfrunner.sh script (also part of the CeroWrtScripts bundle) simulates the RRUL test by creating four simultaneous upload and download streams. This measures latency during heavy load.
  4. Flent is a tool designed to make consistent and repeatable network measurements. Its suite of tests, including RRUL, log the data, and produce attractive graphs of the results. (RRUL specifies that multiple netperf sessions run simultaneously to heavily load the network in both directions.)
  5. The netperf program underlies betterspeedtest.sh, netperfrunner.sh, and Flent, and is built into the CeroWrt firmware. netperf drives traffic through a network and measures its performance.
  6. Netalyzr from icsi.berkeley.edu is a powerful network measurement and diagnostic tool that contributes its data to a large survey of network conditions. However, we have seen its estimate of bufferbloat can be inaccurate: even though netalyzr reports a 1000 msec “buffer measurement”, a concurrent ping test does not show an appreciable change to the responsiveness.
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Comcast Research Innovation Fund
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Bufferbloat Related Projects

Congestion Control Blog
Lede Project (OpenWrt)
Flent Network Test Suite
The Cake shaper

Network Performance Related Resources

Jim Gettys' Blog - The chairman of the Fjord
Toke's Blog - Karlstad University's work on bloat
Voip Users Conference - Weekly Videoconference mostly about voip
Candelatech - A wifi testing company that "gets it".