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I want to test a device for its throughput. Therefore, I am using iperf3. After sending data for 10 seconds, my server reports receiving the same amount of data but at a lower speed than the client.

client: (917 Mbit/s)

[  4]   7.00-8.00   sec   109 MBytes   912 Mbits/sec
[  4]   8.00-9.00   sec   109 MBytes   912 Mbits/sec
[  4]   9.00-10.00  sec   110 MBytes   918 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-10.00  sec  1.07 GBytes   917 Mbits/sec                  sender
[  4]   0.00-10.00  sec  1.07 GBytes   917 Mbits/sec                  receiver

iperf Done.

server: (912 Mbit/s)

...
[  5]   8.00-9.00   sec   110 MBytes   913 Mbits/sec
[  5]   9.00-10.00  sec   109 MBytes   917 Mbits/sec
[  5]  10.00-10.05  sec  5.75 MBytes   920 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth
[  5]   0.00-10.05  sec  0.00 Bytes  0.00 bits/sec                  sender
[  5]   0.00-10.05  sec  1.07 GBytes   912 Mbits/sec                  receiver

Such a difference also occurs with less data sent.

I don't think this makes sense theoretically. If they report transferring the exact same amount of data in the same period of time, why should there be a difference in bandwidth?

Thanks for your help!

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  • Has any answer solved your question? Then please accept it or your question will keep popping up here forever. Please also consider voting for useful answers.
    – Zac67
    Apr 4 at 17:56

1 Answer 1

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They arent taking the exact same amount of time though. The first transfer took 10.00 seconds

0.00-10.00  sec  1.07 GBytes   917 Mbits/sec

The second transfer took 10.05 seconds

0.00-10.05  sec  1.07 GBytes   912 Mbits/sec

Depending on how iperf rounds numbers up and if my maths is correct

912Mbps x 10.05s = 9,165.6Mb which iperf may well round up to 9,170 Mb

9170Mb / 10.00s = 917 Mbps

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