ndt-users list created

[Richard Carlson <>]

Bogdan;

The NDT server was designed to answer questions like, 'why did I get 
these results'.  The server-to-client test generates a detailed set of 
diagnostic messages and outputs a collection of TCP kernel variables to 
help explain what happened.

If you are using the Java client, then click on the 'More Details' and 
'Statistics' buttons to bring up the results.  If you are using the 
command line client the add the -l or -ll options to get the same results.

If the connection is loosing packets, the details will show what the 
loss rate is, how often the loss occurs, if the connection is buffer 
limited instead of limited by the congestion control algorithm, and a 
suite of other details.

You can also run the server with the --snaplog option to capture a trace 
file showing all 120+ web100 variables captured in 5 msec increments. 
Want to know how the TCP congestion window is growing or not, look at 
the snaplog file after the test completes.

If you post the output of the -ll option, or the statistics page, we can 
help you interpret the results.

Rich

On 06/11/2013 11:44 AM, 

 wrote:
> Hello
>
> I've been testing a couple of ADSL 80/20Mbps lines using NDT and I'm
> consistently getting very good averages/small variations for the uplink speed
> (around 16Mbps), but poor estimates (30-40Mbps) for the downlink speed,
> regardless of the server used. The performance appears to be consistent for
> the same server, but varies from server to server (e.g. testing on serverA and
> server, the average on serverA would be 32Mbps and the average on serverB
> would be 37Mbps, with <3Mbps variation); RTT varies slightly between servers,
> 25-50ms. I've tested the lines using both wget and speedtest.net and been
> getting consistently around 50-60Mbps, which is rather far from the NDT
> estimates.
>
> To check for consistency, I setup an NDT server on a remote network with Gb
> connectivity and got around 20-40Mbps NDT estimate and around 45-60Mbps
> download speed using wget.
>
> Looking at the packet trace on the client, the transfer goes fine with 2-3
> exceptions where it stalls rather badly due to packet loss/recovery.
>
> I've used 3.6.3 and 3.6.5.1 for the NDT clients (using the more recent version
> did not seem to make any difference)
>
> Did I miss something in my tests/analysis? Any suggestions?
>
> Best regards
> Bogdan