FreeRADIUS with EAP/TLS authenticating Windows XP Clients - slow authentication

Hi!

To secure my WLAN, I installed a FreeRADIUS Server and configured it as
described in this HOWTO:
http://www.impossiblereflex.com/8021x/eap-tls-HOWTO.htm
Now it _does_ work, but the authentication seems to be _very_ slow. The
authentications runs for about 30 seconds, before it ist finished and I can
access the Network. It doesn't seem to be a CPU-performance problem, because
both the Linux-server which runs RADIUS, and the XP Client are running in
idle-state for most of the time, while authenticating the user.
The WLAN-AP is a SMC Barricade 2804WBR, the NB uses the Centrino-WLAN
Chipset.
Any ideas what could be the cause? Or ist this slow authentication "normal"?

regards,
Stephan