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low estimate for downlink on 80/20MBps line


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  • Subject: low estimate for downlink on 80/20MBps line
  • Date: Tue, 11 Jun 2013 11:44:33 -0400 (EDT)

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



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