Thanks a lot for all the responses!

Meanwhile, I found a iij-ppp version in the FreeBSD source-tree,
which seems to be more recent than the 'current' release of iij-pppi (V0.94).
So, I extracted it from the FreeBSD-tree and tried to compile it.
After some minor modification, it succeeded! :-)
My ppp.conf setup is based on the examples of iij-ppp-0.94.

And I can say:  IT WORKS!

Because I'm using a low-performance serial port (without FIFO!), I can't
say anything about throughput...

But, why isn't it included in the NetBSD distribution ?
IMHO, things like PPP shoudn't be accomplished by the kernel but by
any user process.

Best regards,

Patric.