Strange measurement results

[Jim Carter]

On Tue, 28 May 2002 matriedel at gmx.de wrote:
> I made with my Orinoco silver card some measurements with iperf under
> Linux 2.4.18 with the latest pcmcia package and wireless tools package.
> The result I got is quite strange.  I forced the card to run with a Bit Rate
> of 2Mb/s.
> Iwconfig shows this "Bit Rate=2Mb/s" - but the measurement tells me that the
> transfer rate is
> 5.2 Mbits/sec. It seems that an enforced bit rate has no effect on the real
> transfer rate.
> Has anyone an idea if this is a bug or a feature????

As I understand it, when your card sends out the big packets it really does
honor the rate you set, but if the partner is sending the packets, the
partner picks the speed.  Your ACKs will go at the speed you set, though,
but they are short and don't slow down the transfer very much.

There's been some discussion on the list about just when a parameter change
takes effect, and most likely it's different on different firmware (and
versions, and different parameters?) The safest way is to "ifconfig eth1
down", set the speed with iwconfig, then bring the interface up again.
The fact that the RID on the card shows a particular speed, doesn't mean
that the card has taken your command to heart yet.

James F. Carter          Voice 310 825 2897    FAX 310 206 6673
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