performance question

Jim Carter jimc at
Fri Sep 13 03:31:42 EST 2002

On Wed, 11 Sep 2002, Marc Cousin wrote:
> ok, here's a sum up of what happens here ...
> i've got 2 machines, a debian and a gentoo, both with a 3Com airconnect.
> on those machines, i've been trying to use hostap, orinoco12c, orinoco11b
> (after modifying orinoco_plx to have the pci id of the 3com card the same way
> it is done with 12c driver)

What kernel version does each one have?  What version of wireless tools?
When in doubt, install the latest version of wireless tools.  Also, very
important, what are the vendor and model number of your wireless cards, and
what firmware type and version do they use (e.g. Lucent/Agere 6.16;
Intersil 1.0.3).  The orinoco driver reports this on syslog when starting

> i think the debian machine works perfectly, in all modes, with all drivers,
> and that the gentoo machine is the real problem :
> if i put the debian as an AP (using hostap), the gentoo can connect using
> either driver, except from the very high cpu load i mentionned in the
> previous mail

It looks like you're doing it correctly, except for the broken orinoco
0.12* driver.  Revert to 0.11b.  The Gentoo machine is in Managed mode,
right, when the Debian one is being a host-AP?

> if i put the debian in ad-hoc mode, i cannot connect with either orinoco
> driver, but i can connect with the hostap driver.

In some cases the machine in Ad-Hoc mode will be able to talk with an
access point, but it isn't the right way to do it.  You should be able to
connect if both machines are in Ad-Hoc mode, and the channels are
explicitly set to the same value, and the WEP keys are equal or are turned
off.  Take the default for speed; the cards will negotiate the highest
feasible value, which is 11 Mb for normal home or office installations.
Use iwconfig to check if you set everything up the same on both ends.
Unfortunately there are bugs in some vendors' Ad-Hoc code; for example, I
had endless trouble getting a Dell (Agere) card to work with a Linksys
(Intersil) card in Ad-Hoc mode.  (I finally gave up and bought an
inexpensive AP.)

> what suprises me most is
> that i don't have the same behaviour on both machines. for instance, i can
> change the channel on the debian, but i don't on the gentoo (it accepts the
> command, but iwconfig still tells me the frequency is 2.462, should i put
> channel 10, 11, 12 or 13.)

The access point controls which channel. The client (in Managed mode)
should ignore any channel set into its card, and should automatically
follow the AP.

> another thing i noticed : when i use the orinoco 11b driver, if i put my card
> in managed mode, iwconfig tells there is a signal, if i put it in ad-hoc
> mode, it says there is no signal anymore.

That's not a bug, that's a feature :-)  In managed mode, there's a
particular station (the access point) whose signal should be reported.  In
Ad-Hoc mode there's no fixed partner in the general case, so link quality
reports would be meaningless.  You can use iwspy to designate which partner
should be reported.  There's a plan to include an "autospy" feature which
will be helpful in the common case of an Ad-Hoc net with exactly two
stations, but other areas in the driver have a lot higher priority for
development, like the locking scheme.

James F. Carter          Voice 310 825 2897    FAX 310 206 6673
UCLA-Mathnet;  6115 MSA; 405 Hilgard Ave.; Los Angeles, CA, USA  90095-1555
Email: jimc at (q.v. for PGP key)

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