HiSax modem emulation: X.75-connection brakes down

Hi there,

I have two PCs running, each connected to a ISDN-PBX (Octopus E Modell 
300/800).

PC Bo: HFC PCI card, Debian squeeze
PC Ket: Windows with a VM (Debian squeeze), HFC-USB

I'm connecting to the PBX using the modememulation to do stuff over a 
X.75-connection.
I'm using the following process:

-> minicom -D /dev/ttyI0
Initialize the emulation
-> socat
for access via TCP/IP
-> screen and telnet
to connect and have a running session when no one is logged in.

As long as there is a running connection, the PBX sends data to the PC 
once a minute, so there should'nt be any idle-timeout-issue.

While this construct runs fine on PC Bo, I have some problems with PC Ket.

First: I didn't manage to get isdnlog and Co running, even the ttyI*'s 
were not created. I'm creating the device manually with
mknod -m 660 /dev/ttyI0 c 43 0

Second: HiSax doesn't fully come up. Even after a restart, about every 
second boot the recognition of the card seems not to run right and the 
following lines in dmesg are MISSING:
HiSax: Card 1 Protocol EDSS1 Id=hfc_usb0 (0)
HiSax: DSS1 Rev. 2.32.2.3
HiSax: 2 channels added
HiSax: MAX_WAITING_CALLS added

Re-loading the hfc_usb or hisax-kernelmodules doesn't really help then, 
the only thing I can do is to reboot the machine.

Third: The most disturbing issue is: after a couple of minutes the 
connection gets killed with the messages "NO CARRIER". When I try to do 
a reconnect, the message again is "NO CARRIER" and the kernel logs:
isdn: hfc_usb0,ch0 cause: E0010

Again, after the connection broke down, the only thing left to me seems 
to again reboot the system.

So I wonder what could be the problem:
- installation/configuration of HiSax/etc.?
- hardware issue with the HFC USB ISDN-card? There are some messages of 
the hfc_usb-kernelmodule:
HFC-S USB: driver module revision 2.3.2.24 date 2007/10/14 loaded, (debug=0)
HFC-S USB: probing interface(0) actalt(0) minor(-1)
hfc_usb: probe of 2-2.1:1.0 failed with error -5
HFC-S USB: probing interface(1) actalt(0) minor(-1)
HFC-S USB: detected "Billion tiny USB ISDN TA 128"
- issue caused by the virtualization?

Thanks in advance,

Jens