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:
- 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.
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)
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.
- 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
- 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.
- 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.
- 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
- 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.
- 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.