If memory serves me right, Michael Fox wrote:
> The iperf3 bandwidth option doesn't seem to work (or perhaps I'm not using
> it correctly).
> 
> iPerf3 version 3.1.3 on Ubuntu server and Windows client.
> 
> I'm trying to test radio links at various bandwidths, ranging from 32 Kbps
> to 400 Kbps, and various packet sizes, ranging from 256 to 1520 bytes.  But
> setting the bandwidth down to the link bandwidth (or lower) doesn't slow the
> output from the client.
> 
> Example:  In the example below, bandwidth is clearly set at 128K, but
> resulting bandwidth in 200K.
> 
> How do I get the iperf client to only send at the specified rate?

I think the #1 thing you should try is to get newer executables of
iperf3.  Starting with iperf-3.2 (3.5 is current now) we re-tuned a
bunch of stuff with how the transmitter side paces stuff (or rather we
made it so it isn't so horribly broken).  The use cases where this
really helps is for UDP, which tended to send packets in huge bursts,
and also had difficulty sending at very low bitrates as you are doing.
(iperf3 was originally designed for high-speed environments, such as
multiple-10Gbps.)

If this doesn't work, sending smaller packets might help, although I
think controlling the packet size is part of your tests, so that might
not be feasible.

Bruce.

>> iperf3 -c 192.168.8.10 -u -l 1472 -b 128K
> Connecting to host 192.168.8.10, port 5201
> [  4] local 192.168.7.147 port 59396 connected to 192.168.8.10 port 5201
> [ ID] Interval           Transfer     Bandwidth       Total Datagrams
> [  4]   0.00-1.00   sec  25.9 KBytes   212 Kbits/sec  18
> [  4]   1.00-2.00   sec  24.4 KBytes   200 Kbits/sec  17
> [  4]   2.00-3.00   sec  24.4 KBytes   200 Kbits/sec  17
> [  4]   3.00-4.00   sec  25.9 KBytes   212 Kbits/sec  18
> [  4]   4.00-5.00   sec  21.6 KBytes   177 Kbits/sec  15
> [  4]   5.00-6.00   sec  24.4 KBytes   200 Kbits/sec  17
> [  4]   6.00-7.00   sec  21.6 KBytes   176 Kbits/sec  15
> [  4]   7.00-8.00   sec  24.4 KBytes   200 Kbits/sec  17
> [  4]   8.00-9.00   sec  23.0 KBytes   189 Kbits/sec  16
> [  4]   9.00-10.00  sec  23.0 KBytes   188 Kbits/sec  16
> - - - - - - - - - - - - - - - - - - - - - - - - -
> [ ID] Interval           Transfer     Bandwidth       Jitter    Lost/Total
> Datagrams
> [  4]   0.00-10.00  sec   239 KBytes   195 Kbits/sec  0.049 ms  0/165 (0%)
> [  4] Sent 165 datagrams
> 
> iperf Done.
> 
> 
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